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The Journal of the Institution of Highway Engineers

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British Steel Corporation.

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August 1970

Volume XVII Number 8

The Journal of the Institution. of Highway Engineers

contents
A Review of Small Span Highway Bridge Design and Standardisation A. D. Holland, T.D., B.Se., F.I.C.E., F.I.Struct.E., M.lnst.H.E., and T. L. G. Deuce, M.I.C.E., Dip.T.E., M.lnst.H.E.

3

The Analysis and Design 01 Short Span Skew Highway Bridge Slabs J. Harrop, Ph.D.. B.Sc., M.I.C.E., and N. J. Smithers. M.Sc., M.I.C.E., M.I.Struct.E. The Effect of Work Study and Financial Incentives in Highway Maintenance R. S. Tricker, M.I.W.S.P.. M.R.S.H.

33 41

The Institution of Highway Engineers, 14 Queen Anne's Gate, London SW1 President: H. K. Scott, M.B.E., B.Sc., F.I.C.E., F.lnst.H.E. Secretary: M. J. Hall, M.A., F.C.I.S. The Journal of the Institution of Highway Engineers is published monthly for the Institution of Highway Engineers by Pergamon Press Ltd.

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All editorial communications should be addressed to The Editor, The Journal of the Institution of Highway Engineers, 14 Queen Anne's Gate. London SW1 Telephone 01-839 3582 Advertising and Production Pergamon Press Ltd., Pergamon House, 348-350 Grays Inn Road, London SW1 Telephone 01-837 6484 Subscriptions £5 5s or $13.50 Subscription Enquiries Pergamon Press Ltd., Headington Hill Hall, Oxford Pergamon Press Inc., Maxwell House, Fairview Park, Elmsford, New York

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Joint Meeting, Institution of Highway Engineers and Institution of Structural Engineers.

A Review of Small Span Highway Bridge Oesign and Standardisation
A. D. Holland, T.D., B.Sc .• F.I.C.E .• F.I.Struct.E., M.I.C.E., Dip.T.E., M.lnst.H.E. M.lnst.H.E., and T. l. G. Deuce.

A. D. Hofland

T. L. G. Deuce

BIOGRAPHIES Mr Holland graduated at Bristol University and, following appointments with the Great Western Railway and Devon County Council, joined the Ministry of Transport, Divisional Road Engineer's Office, Manchester in 1937. He transferred to the Bridge Section at the London headquarters of the Ministry in the following year, After war service with the Royal Engineers, 1939-1946 in the United Kingdom, North Africa and Italy he rejoined the Ministry's Bridge Section in 1947. He was appointed Divisional Road Engineer, North Midland Division in 1961 and returned to take charge of the Bridges Division in 1963. The post was subsequently upgraded to that of Deputy Chief Engineer. Mr Holland is the author of a number of Papers on bridges, he was elected to Membership of the Institution in 1968. Mr Deuce was educated at Dollar Academy and served a five year civil engineering apprenticeship with Sir William Arrol and Co. Ltd., Glasgow. After holding a National Service Commission in the Airfield Construction Branch of the Royal Air Force he returned to Arro/'s as a design engineer and worked on a variety of heavy steel structures including bridges, dock gates, caissons, hammerhead cranes and industrial buildings. Subsequent to designing the climbing crane structures and other erection equipment for the towers of the Forth and Severn Bridges he joined the West Riding County Council at the beginning of 1962 and worked on composite reinforced and prestressedconcrete bridges. He was promoted to Principal Assistant in 1964 and was seconded to the Ministry of Transport as Superintending Bridge Engineer at the North-Eastern Road Construction Unit Headquarters in 1968. Later the same year he was appointed Assistant Chief Engineer at the Ministry of Transport where he is now Head of the Bridges Engineering Design Standard Division.
AUGU5T 1970

Mr Deuce was one of the authors contributing to the Institution's third National Conference held iri December, 1969 on the theme of "The Economics of Highway Maintenance" . SU M MARY An analysis of 660 bridges put out to contract during the period 1967 to 1969 is presented in diagrammatic form. Of the decks 63 per cent make use of some form of prefabricated member and 37 per cent are of in situ construction. Because of the difficulties in deriving accurate costs from bills priced in the traditional manner cost studies have been undertaken in co-operation with the Federation of Civil Engineering Contractors. Reference is made to the results of the first of these studies and to a further study commenced in January, 1970. The types of construction under study are descr ib ed and these include decks incorporating the new range of standard bridge beams and also composite steel and concrete designs prepared by the British Steel Corporation and the British Constructional Steelwork Association. Analytical methods currently in use for the more common forms of construction are discussed. Note is taken of the degree of standardisation achieved in regard to bridge ancillaries which can account for 12 to 20 per cent of the cost of a medium span structure. Of the bridges 75 per cent of those analysed are within the span ranges catered for by the designs in the cost study. The use of "preferred designs"for these would make skills available for the design of bridges beyond this limit which can be' expected to increase in number in pro. portion to the forecast increase in expenditure. This Paper was presented at a Joint Meeting of the Institution and the Institution of Structural Engineers in London on April 3rd. 1970. Major H. K. Scott. M.B.£., B.Sc.• F.I.C.E., F.lnst. H. E., County Surveyor of Londonderry and Senior Vice-President of the Institution was in the Chair.
THE JOURNAL OF THE INSTITUTION OF HIGHWAY ENGINEERS

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A Review of Small Span Highway Bridge Design and Standardisation
BACKGROUND Rate of Construction I. The Road Programme. Expenditure on major improvements and new construction on all roads in England for 1966/67 and 1967/68. provisional expenditure for 1968/69 anr forecast expenditure for 1969/70 is given below. the total expenditure on highway schemes in rural areas and about 30 per cent in urban areas. 3. As at December 31st 1969600 miles of motorway accounted for 1,654 bridges. This represents an average of 1.29 bridges/mile over and 1.46 bridges/mile under a motorway. 4. Bridge designs fina1ised for motorways, trunk roads and principal roads during the financial years 1965/69 were as follows:-

TABLE 1 TABLE 2 Year 1966/67 1967/68 1968/69 ( Prov) £(m) Central Funds £(m) LA Funds £(m) Total Year Prestressed Concrete Rein forced Concrete
M

134.7 197.3 210.6 250

30.2 55.4 65.0 75

164.9 252.7 275.6 325

Steel and Composite

Total

1969/70
(Civil Estimates)

1965/66 1966/67 1967/68

1968/69

139 263 321 388

175 151 291 211

102 88 111 112

416 502 723 711

The amount invested in urban road construction has ~ steadily increased in recent years and this trend is expected to continue during the 1970's. 2. Structures .on average account for about 25 per cent of

FORMS OF CONSTRUCTION USED 5. Analyses of the deck construction of a substantial proportion of motorway and trunk road bridges put out to contract during 1967-1969 are given in Figures 1-4 as follows: ~

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AUGUST 1970

THE JOURNAL OF THE INSTITUTION OF HIGHWAY ENGINEERS

A Review of Small Span Highway Bridge Design and Standardisation
GROUP A Bridges making use of prefabricated members Bridges of insitu construction 21 6 Overbridges (546 spans) Fig 1 201 Underbridges (350 spans) .Fig2 1440verbridges (499 spans) Fig 3 99 Underbridges (141 spans) Fig4 ments are characterised by rate variations of the kind quoted above, the position in respect of more complicated items of work milst be considerably more disparate, and the selection of appropriate rates to use in estimating even more liable to error. ]4. The Method of Measurement for Road and Bridge Works which the Ministry is to publish this year will introduce stan. dard measurement and billing for the Ministry's contracts in a rationalised form. The grouping of bridgeworks items in the format prescribed will have recognisable group costa. bility, and the items within the groups have costing potential which contractors may recognise within their own systems. If they do this should go a considerable way towards remedying the present inaccurate knowledge of true costs. 15. One aspect of the Ministry's Method of Measurement which .should improve the reliability and usefulness of collected data is the fact that it requires designs to be fully detailed at the time tenders are invited. This is a practice which is already followed by many engineers but it is by no means generally the case. 16. C]early it will be some time before cost data reflecting the influence of the new Met.hod of Measurement becomes avail. able. In the meantime an alternative approach to design/cost study was made possible by, the helpful co-operation of the Federation of Civil Engineering Contractors (FCEC). As an exception to their general rule the Federation assisted in arranging for a series of superstructure designs to be priced by four major contractors on a confidential basis in the same way as normal tenders, so that all designs had common dimensions and were compared under common conditions of time and location. 17. This study compared the cost of reinforced concrete and prestressed inverted T beams at two span ranges 12m (40 ft) and 18m (60 it) for various arrangements of solid and hollow slabs. Standard Prestressed Concrete Development Group (PCDG) beams were used for the 12m span and modified versions for the] 8m span. The results have been published elsewhere (1) but will be briefly referred to in the following sections. REVIEW Principal Deck Forms ] 8. Solid Slabs The types of construction referred to in Paragraph 8 all have some form of concrete slab beneath the wear. ing surface. The competitiveness of the simplest type viz in situ reinforced concrete solid slab is largely dependent on the cost and acceptability of temporary support. 19. Solid composite slabs formed from prestressed inverted T beams infilled with reinforced concrete dispense with the need for falsework and shuttering and by minimising inter. ference to traffic underneath result in a competitive form of construction. 20. The cost study indicated that the solid reinforced concrete slab could be competitive at 12m span and slightly less so at ] 8m. For the solid slabs using the PCDa prestressed inverted T beams there was little difference in cost between the use of lightweight and normal concrete infill for 12m span but lightweight concrete was. shown as being marginally cheaper at 18m span. 21. Approved methods for analysing the distribution of both HA and HB loading include the Morice and Little (2) and Rusch and Hergenroder (3) manual methods and finite element and grillage computer methods. The Morice and Little method based on distribution coefficients is primarily intended for right slab bridge decks but it is an accepted form of analysis for skews of up to 20°. Rusch and Hergenroder's method for skew slabs depends on a series of influence moment diagrams derived by experiment. The diagrams are related to specific angles of skew and the analysis of decks with intermediate angles has to be interpolated. 22. Both methods are limited to simply supported decks with parallel abutments and parallel sides. These limitations are overcome bv the finite element computer programs which
AUGUST 197D

1

GROUP

B

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A similar analysis for 28 viaducts (933 spans) is given in Figure

6. A summary of these analyses is given in Tables 3 to 5 relating to each of the groups designated in paragraph 5. It will be seen that the respective totals for the 660 bridges are Group A 417, and Group B 243. 7. The results can be further summarised in Tab]e 6. TABLE 6 Group Group

A
(i) Solid Slab (ii) Voided Slab (jii) Beam and Slab (iv) Cellular Box (v) Other 155 43 161 40 18

Total 285 80 165 84 46

B
130 - 37 4 44 28

,8. The content of this Paper is principally concerned with categories (i) - (iii) above. COSTS 9. As already indicated, bridgeworks in motorway and trunk road contracts constitute between about 20 and 30 per cent of the total contract value although the lowest tender price for bridgeworks is not necessarily the price quoted in the lowest overall tender. The situation has not been subjected to. a comprehensive analysis but it is thought to occur fairly frequently .• 10. Where alternative designs have been put out to tender _ usually to compare a steel design with a concrete one - the tenderers have not been consistent in their cost-order placing of the alternatives. It has happened for example that the next lowest tender to a winning concrete tender was one for the steel alternative, with concrete returning as the third lowest. 11. The pricing of items of work in Bills of Quantities is so varied as to make comparisons of unit price between one contract and another extremely difficult. One sequence of operations sufficiently common to many types of bridge construction in order to make an analysis possible is the construction of reinforced concrete deck slabs. ] 2. An analysis of the current rates for in situ concrete and 3 sizes of bar reinforcement extracted from 27 motorway and trunk road contracts let in ]967 showed that the price ranges for these four items varied between:!:: 23, and:!:: 36 per cent of the average. The valid estimating ranges were shown to be:Concrete/cu yd ~ in. dia. reinf/cwt
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123/. to 178/92/. to 119/-

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13. Concrete and reinforcement in slab construction are straightforward elements of work that present no great costing problems to contractors and involve .routines of work that are more or less standard to all Ministry contracts. If these eleB

THE JOURNAL

OF THE INSTITUTION

OF HIGHWAY

ENGINEERS

I~ ~ , ~
I

A Review of Small Span Highway Bridge Design and Standardisation

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FIG 4. UNDERBRIDGES OF INSITU CONSTRUCTION - (1967- 69)

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enable any shape of simply supported or continuous deck on random supports to be analysed. The less powerful grillage programs. whilst more economical in running time. are only appropriate for the analysis of decks which can be accurately simulated by a grillage layout. In practice most slab decks are analysed by the Morice and Little method whenever applicable either manually or by one of the computerised versions (4) or by one of the other computer methods already referred to. 23. A suite of distribution analysis programs is being deve. loped by the Ministry in order to ensure that reliable computer methods are readily available. The first program (5) in this suite is for simply or continuously supported slab decks on random supports. It is to be followed by a series of grillage programs capable of analysing straight or curved decks of uniform or variable depth. 24. In Situ Reinforced Concrete Voided Slabs. The introduction of voids into slabs to improve efficiency and save material is obviously advantageous although the early proprietary void formers presented concreting difficulties and their cost tended to' balance that of the concrete they displaced. Nevertheless the reduction in deadweight leads to an increase in overall efficiency. At 18m span this design was priced lowest of the seven alternatives studied. Design methods generally are as stated in Paragraphs 21-23 above. 25. Composite Cellular Decks. Three forms of composite cellular deck now in use are shown in Figure 6. Figure 6(a) may be described as a composite voided slab. and Figure 6(b) as a voided contiguous inverted T beam deck. Functionally this is slightly less efficient than the former, but where the small increase in construction depth can be accepted the omission of bottom reinforcement and surroundtngs jn situ concrete offsets the increase depth of beam necessitated by the reduced distribution efficiency. 26. The type shown in Figure 6(a) was shown to be marginally
....UGUST 1970

more expensive than the slab decks at 12m span and markedly more so at 18m. The type shown in Figure 6(b) was not included in the study. 27. The cost effectiveness of both these forms was one of the principal factors considered when the new range (6) of Standard Bridge Beams was under development by the Ministry and the Cement and Concrete Association for the span range 15-29m. A handbook giving full details of the new sections and design calculations is currently being prepared. 28. The third form, Figure 6(c) is a continuous precast box shear key deck. An analysis technique proposed by Dr. Spindel (7) has provided a straightforward and rational design method. Although the functional efficiency is rather lower than those shown in Figures 6(a) and 6(b) it can neverthelesss prove a worthwhile form of construction in some locations. 29. Cost. At both 12m and 18m the cost of composite cellular construction was shown to be greater than for solid composite slabs. The prices quoted allowed in all cases for false. work to be designed so as to avoid obstruction to construction plant to accord with the contractor's own requirements. No account was taken however of the possible need to comply with special requirements of road or rail traffic. Dcsign, With the exception of the Rusch and Hergenroder method the accepted forms of analysis are generally as stated in Paragraphs 21-23 above. 30. In Situ Cellular Construction. This form of design using a larger void to concrete ratio than can be provided with circular void formers, and therefore still further reducing the dead loan, is similarly likely to prove competitive depending upon the cost of the formwork and acceptability of the falsework. JI. Concrete Beam and Slab. The traditional in situ reinforced concrete beam and slab deck has now been largely superseded by the composite precast beam and in situ slab. Analytically this is similar in form to that shown in Figure 6(b), the number
THE JOURN ....L Of THE INSTITUTION OF HIGHW ....y ENGINEERS 9

A Review of Small Span Highway Bridge Design and Standardisation
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and size of the beams being determined by their spacing. Transverse diaphragms are now normally omitted except over supports. 32. Up to 29m span competitiveness with the cellular forms of deck will be largely governed by the importance of achieving minimum construction depth and the effect which any greater depth may have on overall cost. 33. Composite Steel and Concrete. The British Constructional Steelwork Association have issued charts as a preliminary basis for design giving alternative section sizes of universal beams in high yield stress steel for two categories of loading (HA and 45 units of HB) and two widths of carriageway lane of 12 it and 10 it (3.65m and 3 m). Appropriate thickness of concrete deck slabs in combination with variations in beam spacing are presented for a span range of 25 to 100 ft (7.5m to 30m). 34. In preparing these charts consideration was given to the relative advantages of either using BS.l53 factor distribution for HB loading or alternatively of making provision in the de. sign for an optimised transverse distribution of load which could be expected to minimise deck materials. However the design aid nature of the. charts made it inappropriate to correlate them with the wide range of possible bridge widths and layout and this led to the adoption of the simpler approach as representing reasonably typical solutions. 35. This was shown at the time to be a good compromise between the dictates of economy and realistic design on the basis of the design knowledge then available. It is hoped that present uncertainties as to the correct method to be adopted
AUGUST 1970

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THE JOURNAL OF THE INSTITUTION OF HIGHWAY ENGINEERS

.

,
FIG. No.7

A Review of Small Span Highway Bridge Design and Slandardisation
for analysis of the slab will be resolved by studies currently in progress (see paragraph 41 below). 36. Figure 7 shows the weIght of steel per sq m of deck area for a proportion of the steel bridges referred to in Figures 1 and 2 and indicates the type of construction used, the loading being either HA or HE. For purposes of comparison values have been inserted from the B.C.S.A. tables referred to in Paragraph 33. 37. Prellex. Use is also made of the well-known preflexed concrete cased steel beams where construction depth is at a premium and where particular economic advantage is gained from the elimination of the need for periodic painting e.g. for methods(9) which, with their greater accuracy, will, in general. provide a more economic design. 40. Edge Stiffness. The prescribed horizontal clearance between parapet and edge of carriageway or hard shoulder should be regarded as a minimum. There is no objection to this being exceeded in cases where it produces a more economical overall solution. LOCAL STRESSES 41. The tendency, through the permitted distribution of HA loading, is for steel beam spacings to increase to 10 or

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highway bridges over railways with overhead electrification. Approved methods for ana]ysing the distribution of HA and HB loading include the Morice and Little and Hendry and Jaeger(8) manual methods and the computer methods referred to in Paragraph 23. The limitations on the Morice and Little method for concrete beam and slab decks are the same as for slab analysis. Although it is not strictly applicable for steel beam and slab decks it can be used with reasonable accuracy within the same limitations as those for concrete. The Hendry and Jaeger method based on harmonic analysis allows beam and slab decks, in particular those uSing steel with parallel sides and parallel abutments, to be analysed without restriction on skew. 39. In practice as in the case of slab decks finite element and grillage computer analysis methods are the most powerful and are being adopted more widely, although the Morice and Little analysis is still used extensively. Some beam and slab decks with skews of over 20° are still on occasion designed on the basis of the BS.]53 distribution factors, but this is to be discouraged in favour of the recommended computer grillage
AUGUST 1910

12 feet (3m or 3.65m) and this, together with the omission of transverse intermediate diaphragms, has highlighted the need to investigate the co-existent stresses arising from transverse distribution and local bending moments. Superposition of the results of computer analyses of these two effects has demonstrated that the algebraic sum of local wheel load moments derived by Westergaard analysis and the moments arising from transverse distribution of load between beams is excessive. The indications are that a more accurate analysis of these combined effects will result in worthwhile savings in the cost of deck slabs and research into this has been commissioned by the Ministry. PRECAST BEAMS 42. Of the concrete beams proposed as national standards hitherto the inverted T beams have been by far the most widely used. Apart from the P.CD.G. beams various authorities have developed standard ranges of their own as in the West Riding (I beams) and Cheshire (inverted T beams). It is the authors' opinion that there is scope for both inverted
THE JOURNAL OF THE INSTITUTION OF HIGHWAY ENGINEERS IJ

-

A Review of Small Span Highway Bridge Design and Standardisation
T and I beams for use in the 15 to 29m span ranges. The inverted T beam sections have already been developed and promulgated and it is intended that these will be followed in due course by a range of I beams modelled on those developed by the Wffit Riding County Council with due account being taken of criticism of the previous P.C.D.G. range. The designS referred to in Paragraph 27 require the use of deflected . tendons for the upper range of span. For the lower range it will be interesting to see whether straight tendons retain economic advantage. 43. Modifications to standard beams invariably result in additional cost. Following consultation with the precast concrete manufacturing industry the Cement and Concrete Association have prepared a Table showing what the commonest forms of modification necessitate in terms of extra work and materials and the approximate percentage cost increase likely to arise. By courtesy of the Association the Table is reproduced at Appendix A STUDIES CURRENTLYIN HAND ,44. The Federation of Civil Engineering Contractors is currently co-operating in the pricing of further designs. These designs have been selected under the aegis of the Ministry's /' Bridge Design Committee and will give comparative prices for :(a) Composite cellular decks types shown in Figures 6(a) and 6(b) using the new standard beams for single spans of 15m, 23m and 29m, i.e. the extremes of the range for which the beams are intended, together with an intermediate value. A 22m width of deck has been used for both types and additionally a width of 9m for the type at Figure 6(a) so as to test costs at extremes of width. A 4-span simply supported bridge of the type at Figure 6(a) with a deck width of 22m and spans - of 15m and 23m has also been included. (b) Simply supported single and 4-span composite steel decks having individual spans and widths as above, and a further 4-span bridge having a width of 22m with spans of 23m and 29m. The designs for these have been prepared by the British Steel Corporation and the British Constructional Steelwork Associa tion. (c) Four span continuous composite steel deck bridges having a width of 22m and side spans of 15m and 23m and main spans of 23m and 29m respectively. The girders are of asymmetrical welding plate construction. 45. The span lengths are measured centre to centre of bearings, and extremities of width have deliberately been chosen for the single span deck so as to test the least favourable and most favourable load distribution. The loading in every case is HA with a check for 45 units HB. 46. The construction depths are as set out in Table 7. ft is of interest that the construction depth for the new composite voided slab design at 18.3m (60ft) is now 930mm (37in) as compared with 1118mm (44in) for the modified P.C.D.G. beams used previously. 47. All decks are seated on rubber bearing pads and waterproofed in accordance with Ministry of Transport Technical Memorandum BEl. For the simply supported multi-span bridges the surfacing is continuous across the whole bridge, buried joints over the intermediate supports being provided as described in Technical Memorandum BE 6. Particular attention has been paid to the need to minimise the cost. of up-keep. 48. It should be kept in mind that the transport by road of beams having a length in excess of 27.4m is not generally permitted other than for short distances e.g. from a nearby railway siding or precasting yard. 49. The possibility of using Corten steel for the composite steel decks in locations where the atmosphere is free from marine or chemical contamination promises to be economically worthwhile. 50. Prices for the 15m spans will enable correlation to be made with those from' the earlier study and for the longer spans they should show the effectiveness of the new standard bridge beams and the extent of competitiveness between decks using them and those using the composite steel and concrete designs. STANDARDISATION Current Position 51. A fair degree of standardisation is achieved by the wide. spread use of, for example, the Ministry Standard Specification for Road and Bridge Works and the design guidance and requirements contained in Technical Memoranda. 52. Bridge ancillaries, for which design standards have to.date been issued, include parapets, waterproofing, expansion joints, bearings and surface finish, and a Memorandum is currently in preparation dealing with paint protection systems. These ancillary items can account for 12-20 per cent of the cost of a medium span structure. 53. There are in addition the national standard ranges of bot:l steel and concrete bridge beams referred to earlier. It will be noted from Table 3, that of bridge decks using prefabricated members, the proportion using beams to the national standard is 43.5 per cent of the total. Reference to Figures I and 2 show that the large majority of non-standard beams have been used for spans exceeding 15m, for which the new range of prestressed concrete beams has now been introduced, . The proportion of national standard beams used for span:, below 15m is 81 per cent, i.e. 9.8 out of 121. . 54. The Table in the Appendix indicates that the additional costs of modifying standard sections vary from 5 to 22 per cent. Contractors have indicated that additional costs 01' a similar order are attributable to variations in basic design between one bridge and another within a single contract. 55. In the context of surface treatment attention was drawn to this in Technical Memorandum BE2 and much has been achieved in designs prepared since that date to reduce variation within a contract to a mimimum. There would however be similar advantages to be gained from reducing the variation in bridge designs between one contract and other. 56. Of the 662 bridges recorded in Figures 1-4 75 per cent have spans of less than 29m i.e. are within the span ranges catered for by the designs discussed earlier in the Paper. It is for the bridges beyond this span limit i.e. the 25 per cent that the bridge designers expertise is particularly needed, yet the number of such bridges can be expected to increase pro rata to the forecast increas~ in expenditure shown in Table 1. 57. It is reasonable that an attempt should be made to avoid, by means of some form of increased productivity, the need for a comparable increase in staff requirements. This could be achieved by. as a first stage, general use of "preferred designs" for bridges in the low span range i.e. up to 29m.

TABLE 7 CONCRETE SPAN 15m 23m 29m
12

Composite voided slab (mm) 770 1170 1490

Contiguous inverted tee beam and slab (mm) 850 1250 1490

Continuous Composite steel and Concrete (mm) 770 approx 1170 1490
AUGUST 1970

THE JOURNAL OF THE INSTITUTION OF HIGHWAY ENGINEERS

,

A Review of Small Span Highway Bridge Design and Standardisatian
SCOPE 58. Underbridges. Bridges carrying motorways and trunk roads have a greater uniformity of deck width and design loading than bridges over them and the scope for use of "pre ferred designs" is considerable. As will be seen from Figures 2 and 4, 92 per cent of underbridges in the sample are in the span range below 29m. 59. At the same time however, whilst the cost of bridges has no relevance unless considered in conjunction with that of the associated roadworks, it should be noted that the cost of bridges carrying major roads may often be substantially higher than for bridges over them due principally to their higher ratio of substructure to deck area and on occasion also to the different design loadings. Careful cost analysis is therefore needed before deciding how road crossings can be most economically treated. 60. Overbridges. As is shown in Paragraph 3 the incidence of overbridges is lower than for underbridges and at the same time includes a proportion of footbridges and bridges carrying accommodation roads. DESIGN PARAMETERS 61. Loading. The design loading for overbridges carrying highways may be HA, or HA with a check for either 37t or 45 units HB depending upon the category of road carried. The economy of adopting a common design loading is currently under study. 62. Width. Consideration has been given to the adoption of a range of modular widths for overbridges but it has not been found possible to reconcile these with carriageway widths and road layout. A more practical approach would therefore be to prescribe a standard range of deck widths. which will accommodate varieties of layout, and also to arrange that the edge details referred to in Paragraph 75 can tolerate small departures from a standard width. 63. Skew. The horizontal clearance requirement for the main spans of three lane motorway overbridges spanning square to the road generally results in a span of 17.7m (58ft) measured centre to centre of bearings. 64. An analysis of 92 consecutive bridge sites on a section of M62 located in the West Riding and of a random sample of 100 motorway and trunk road bridges yielded the variations in skew shown in Figures 8(a) and 8(b). 65. The effect of skew on the overall length of 17.7m defined in Paragraph 63 is shown in Figure 8(c). The percentage increase in total cost resulting from skew for composite steel and concrete bridges is also shown. The latter has been derived from a Ministry cost model. 66. It will be noted that the 29m span range will cater in the case of bridges over D3 motorways for skews of up to 50 degrees, i.e. on the basis of the analysis referred to in Paragraph 64 for about 95 per cent of the sample, APPEARANCE 67. The form and appearance of .bridges over motorways and trunk roads can in general be seen and noticed by more road users thaf! those on most other roads and consequently they are liable to engender most comment. The views expressed can be extremely varied and even those from a common source may be conflicting and even contradictory. 68. There is, however, clearly a need to avoid monotony resulting from the repetition of dreary intrusions on the field of view ahead. Desirably the forms should be of quiet competence which integrate comfortably with the setting without attracting undue attention either by excess of virtue or lack of it. 69. It is considered that bridges embodying the designs discussed earlier can comply with this criterion. There will in any case be instances where the incidence of skew. site line consideration, or the need to span over a slip road necessitates the use of some other design. In addition there will be the footway and accommodation bridges to give further variety.
AUGUST 1970

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70. There is also scope for variation in treatment of the facings to piers and abutments. As stated in Technical Memorandum BE 2 the finish to exposed concrete may be smooth, textures (using formwork of sawn boarding or lined with plastic sheeting) or exposed aggregate. Masonry may be used for the facing to wing walls with a short return at' each end of the abutment face for bridges located in National Parks. Masonry may similarly be used for a proportion of bridges located in a natural stone producing area. Since the purpose is to provide variety it would be reasonable to select with discrimination not more than half of such bridges for special treatment. METHODS OF PROMULGATION 71. Once it has been decided that a particular design shall be
THE JOUl\NAl OF THE INSTITUTION OF HIGHWAY ENGINEEl\S 13

-

A Review of Small Span Highway Bridge Design and Standardisation
standardised for use as one of a limited number of "preferred designs" the necessary design data would be obtained by' computer programme for an appropriate range of span, width, loading and skew. 72. This programme, together with standard typical drawings, could then be made available for use by'design offices as required, but such procedure would clearly involve a wholly unjustifiable repetitive use of computer time, 73. The alternative is for the computer programmes to be used centrally to produce the whole range of designs, which would be presented, again with drawings of standard details, in tabular or graphical form. This latter method would enable the designs to be produced efficiently and although use of graphical techniques would enable intermediate incremental steps to be determined following the detailed analysis of a small percentage of the designs, the total number of cases which would have to be analysed to cover the full range of span width and skew modules would be formidable. 74. A compromise between the two solutions may well be the most appropriate. This would entail the production, on a centralised basis, of designs for the more common spans, widths and skews which could be augmented by one-off runs of the computer programs, as a necessity arose, for the less common spans, widths and skews at the extremes of the range, The exact procedure to be adopted will turn iargely upon the extent of the ranges indicated by the pilot studies. 75. It is further visualised that a series of standardised edge details, parapets' and other similar features could be made available and their use in differing circumstances would give a selective approach avoiding monotony and enabling some degree of individuality to be incorporated into bridges which wen~ nevertheless standard. 76. There is little difficulty in introducing standardisation at any point in time on such a basis as theoretical design knowledge and practical experience will permit. The benefits of so doing will depend upon the extent of evolution which these two bases have reached. During a period of steady advancement standardisation too early is liable to be quickly out-dated. 77. During the past ten years the scale of bridge building in this country has been substantial and the progress in the evolution of design and construction methods and techniques has been commensurate with this. In the authors' opinion some of the designs which have now evolved and which have been discussed' in this Paper should maintain acceptability through at least the first half of the new decade. 78. It is considered also that a comparatively widespread use could be made of these designs without detriment to amenity standards. Such use would not preclude design offices from putting forward alternatives. Such alternatives could supersede any preferred design demonstrated to represent generally a poorer return on expenditure. ACKN OWLEDG M ENTS Acknowledgment is made to the County Surveyor, West Riding County Council for his co.operation in regard to the information given in Figure 8(a) and to the authors' numerous colleagues in the Ministry for their ready assistance. REFERENCES
(I) Design standards for prestressed concrete bridges. A D

1
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,

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It

!

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I

1

Holland. Proceedings of meeting held 6 June 1967 Concrete Society (see also Present-day Bridge Design Journal of the Institution of Highway Engineers, July 1967). (2) The Analysis of Right Bridge Decks Subjected to Abnormal Loading by P B Morice and G Little - Cement and Concrete Association DblI .. (3) Influence Surfaces for Moments in Skew Slabs H Rusch and A Hergenroder, Cement and Concrete Association. (4) Technical Memorandu,m (Bridge) BE 22 19/9/69. (5) Technical Memorandum (Bridges) BE 18 10/7/69. (6) The new MOT /C&CA standard prestressed bridge beam. Cement and Concrete Association, October 1969. (7) Ministry of Transport Technical Memorandum (Bridges) No. BE 23 (8) The Analysis of Grid Frameworks and related Structures by A W Hendry andL G Jaeger - Chatto and Windus. (9) Technical Memorandum (Bridges) BE 22/1 (to be issued).

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14

THE JOURNAL OF THE INSTITUTION OF HIGHWAY ENGINEERS

AUGUST 1970

\
A Review of Small Span Highway Bridge Design and Standardisation
APPENDIX A COST OF MODIFYING STANDARD SECTIONS (Supplied by Cement and Concrete Association) Additional work to be carried out by the precast concrete manufacturer Cutting standard forms and providing additional special forms Patch-plating standard forms, drilling new holes or providing special side forms Patch-plating standard forms, drilling new holes or providing special side forms Special end stops (drilled on the skew) and making good damage caused to acute corners of the beams when de-tensioning and transporting Additional labour and possible modification to standard side forms Additional cost 20 per cent 10 per cent 10 per cent 5 per cent Comment End blocks are rarely necessary for pretensioned beams Transverse design should be modified to achieve maximum economy, using standard holes or slots Square ends can usually be fitted together - even on skewed intermediate piers Research indicates that roughening is not necessary to obtain satisfactory bond Prestressing normally provides a soffit camber

Modification 1 Blocking out ends 2 Non -sta ndard spacing of transverse holes

3 Non-standard.
sized transverse holes

4 Skew ends

5 Surface roughening to sides

15 per cent

6 Special soffit
camber 7 Special notches and rebates in sides or soffits

Special, complicated soffit and side formsfollowed by binding of concrete to forms during de-tensioning Drilling and making good standard forms

20 per cent 10 per cent 5 per cent

8 Wire instead of
strand for prestressing

Increased handling

Specify force and eccentricity only. Manufacturer will submit proposals

t

9 Re-entrant
diaphragm stubs or horizontal starter bars 10 Vertical holes through webs

As in item 1 above, followed by difficulty in striking forms without permanent damage

22 per cent

Special soffit forms

10 per cent

. Vertical dowels should be located between adjacent beams by blocking out edges of bottom flanges

AUGUST 1970

THE JOURNAL

OF THE INSTITUTION

OF HIGHWAY

ENGINEERS

15

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/
Discussion
THE CHAIRMAN introduced Dr Kerensky of Freeman, Fox & Partners, President-Designate of the Institution of Structural Engineers and a Vice-President of the Institution of Highway Engineers and called upon him to propose a vote of thanks to the authors. DR O. A. KERENSKY (Freeman, Fox & Partners) said it was a pleasure and an honour to propose a vote of thanks to the two authors who had produced an informative and provocative Paper. He was sure that the discussion which he had the privilege to open would raise several queries and, perhaps, some criticisms. Standard highway bridges, the main theme of the Paper, have been advocated or objected to by engineers on many occasions and it almost looked now as if they were trying to close the door after the horse had bolted because some 2,000 bridges had already been built during th~ last few years involving a great deal of mental and phYSIcal effort. However, he thought that the time was just right for settling on a few carefully designed and tried types. But even if they were late, it was better to be late than never. There were, of course, very many more bridges still to be built. Standard bridges should be adopted for a period of years with the door for better ones always left open. The question was which type to make standard? Were too many types being considered? The Paper seemed to favour standard precast units. That was another controversial matter which the speaker was sure would be disputed by many. There was no doubt in his mind that with present prices in England the cast in-situ work came out cheaper. There were many good reasons why, in fact, it should be so. Furthermore, structurally, the composite concrete decks were less efficient than the cast in-situ ones, and therefore required more material. He believed that further attention should be paid to standardising methods of construction and formwork. This applied particularly to slab soffits, columns, piers and abutments. The authors had given a mass of information for comparing the costs of different types of bridges, but accurate pricing was difficult especi~lIy when the cost of other work might depend on the timing of bridgeworks. A more expensive bridge might be economic when considering the contract as a whole. Dr Kerensky said that it gave him a special pleasure to thank the authors for their excellent Paper because its subject was one in which he and they had been involved during the last few years and he was sure that the "discussion would prove of great value to all. The vote of Ithankswas carried with acclamation, DR R E ROWE (Cement and Concrete Association) said he wished to comment on certain aspects of the Paper and would refer to specific paragraphs. Paragraphs 1and 2. He was delighted to see from these that an estimated £100 to £150 million would be spent per annum on bridgeworks during the 1970s. He admitted to having extrapolated slightly beyond the figures quoted in Table I and had assumed that the 18 per cent increase from \968/69 to 1969/70 would continue! Paragraph 20, He wanted to amplify the points made here in relation to the first costing exercise and he referred to the slide shown during the authors' presentation. The range of costs for each of the forms of construction was considerable and the essential details (given in Reference 1 of the Paper) were as follows:
16 THE JOURNAL OF THE INSTITUTION OF HIGHWAY ENGINEERS

Span Form of (m) construct tion*

Depth of Mean cost constructaken as tion 100 per (mm) cent for R,C.

Range (x mean)

in-situ 12
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18
"

*1 2 3 4

" " In situ R.C. PCDG Beams+in-situfill. PCDG Beams lightweight in-situ fill. PCDG Beams in a voided sl,ab.

1 2 3 4 1 2 3 4

685 760
725

825 990 990 1070 1200

100 101 105 119 100 111 106 117

0.92-1.08 0.83-1.12 0.82-1.10 0.86-1.13 0.92-1.08 0.86-1.09 0.87-1.11 0.92-1.11

+

These details highlighted the difficulty, mentioned by the authors, of drawing any definite conclusions. The min.imum costs, for example, showed the type 2 form of constructlOn to be the more competitive. Paragraphs 25 and 26. The authors had discussed the relative merits of voided slab and contiguous beam construction and Dr Rowe said he would merely comment that the construction depth aspect might well be significant. When referring to the voided slab (Figure 6(a)) versus the slab deck it was relevant to point out that the PCDG beams were not designed for this form of construction. If a more appropriate beam section were employed, such as the M beam,. the cost comparison should be more favourable to the vorded slab type of deck. Paragraph 28. The authors had stated that the functional efficiency of the shear key box deck was less than that of the voided slab and voided contiguous inverted T.beam deck. Dr Rowe took issue with this statement since he considered that, if designed properly, it would function more efficiently ~than the voided contiguous inverted T-beam deck and would have a lesser construction depth, as indicated in the slide showing the results of the first cost study. Paragraph 31. Referred to T beam decks being asymmetricall-beams; the Tables presented were most interesting since, contrary to a .previous impression, there was an indication that, relatively speaking, this form of construction was quite widely used. There was also a definite preference for a nonstandard beam to one in the PCDG range. Dr Rowe found the subject of T-beam decks very interesting; other countries - particularly Australia - used these as a standard form of construction, and this had proved most economical. He wondered if the authors would care to comment on the amount of, additional cost which should be paid for increased construction depth, in other words pounds per square' foot per foot of construction depth for bridges in this country. If this point was considered in relation to the first cost study, the figures obtained would look a little different and would possibly go some way to answering Dr Kerensky's point about the relative merits of in-situ versus precast. Paragraph 41. The authors stated that in composite steel/
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Discussion
concrete decks a more refined analysis" of the combined stress condition in the top slap should resuit "in worthwhile savings. In fact, these slabs were mostly designed according to CPI17 rules and more refined analysis would result in heavier slabs. The only way to treat this problem rationally was to re.assess the acceptable levels of stress in the concrete for this particular stress field. It should be noted that any saving resulting from this process would be applicable to aU types of bridge and not just composite steel/concrete. Paragraph 42. This referred to the new type of I-beam under consideration by the Ministry. Dr Rowe said that the Association would be very happy to co-operate on this. Paragraph 46. This returned to the subject of construction depth, and it was here that the two exercises on costing met. The paragraph stated that there was a possible saving of 16 per cent in the construction depth, i.e. 17in. Dr Rowe would assess this, on the basis of figures available to him, as representing about 6s. a square foot. Using the figures from the first cost study, with the four PCDG beams, the cost per square foot of deck was about £3; with the new M beams it would be about £2.6. and this compared very favourable with in-situ. With the new type beam, it had been estimated that the cost per cubic foot of the prestressed concrete units would be 25s.-305. (ex. works). This would make the desk fairly economical. In Table 7 the comparisons given were between simply supported spans and continuous composite steel/concrete decks. The interesting point was that the depth of both decks was the same. The speaker estimated that if he was designing the concrete decks continuously (as Dr Kerensky had sug. gested should be done), there would be a further saving in construction depth of the order of 20-30 per cent, which would reflect on the economics. Dr Rowe said he was a litlle confused concerning Paragraph 65 and asked for some clarification from the authors. They had staled that in the decks the figure showed relative merits of composite steel/concrete and concrete as a function of skew. Was it assumed that the four-span overbridges were steel and the simply supported underbridges concrete? In conclusion Dr Rowe emphasised that in standardisation it was most important, to standardise and optimise the design approach itself and then to provide the standard deck, whether it had standard beams or not. He had been standardising bridges and the PCDG beams were introduced in 1961. The metric versions had now been introduced. Hence these were still satisfactory after a life of nine years. The authors' contention that the standard decks proposed in their Paper would last at least until the end of the I970s, was one the speaker endorsed. MR J MURRAY (Lancashire Sub-Unit North Western Road Construction Unit) congratulated the authors on their Paper which was very clear and readable. He was a little surprised to learn that Dr Kerensky favoured in-siru cast bridges when contractors were facing major difficulties in their construction. Pleas from contractors were received all the time whenever an in-situ cast deck was suggested, and these all took the form "Please make it precast". The speaker understood that they paid their carpenters a pound an hour and, even at these high rates, they were difficult to obtain. For a major motorway containing, say, twenty or thirty small span bridges the contractor faced extreme problems in being able to complete the work on time if it was all in,-situ cast. With precasting there were no difficulties, and the speaker was sure that in time the costs of bridges and precast elements in particular, would fall. In Lancashire, on a major motorway, now at the design stage, there were sixty-two bridges of which fifty-nine contained precast deck elements. Some of these were major bridges, with spans of 140ft.'Figures 1 and 2 of the Paper showed that most of the bridges were simply supported. The speaker agreed that this
AUGUST 1m

was the simplest fOffi] of bridge and yet waterproofing was the only point that worried designers. It was often found that the joints failed because the contractor had not been able to make a good enough job of them, or supervision had been lacking, and the speaker wondered if it was better to design bridges using precast elements which could be simply supported for dead load conditions and continuous for live load conditions. This was a possibility now that deflected tendons were more widely used. It would also avoid leakage of the joints which stained the piers and ruined the appearance of many bridges. In Paragraph 9 the authors had not stated the direct cost of the bridges although this had been explained in an earlier Paper by Mr Holland. At a recent lecture, to which Dr Rowe had referred, it had been said that the cost of I section precast bridge beams had remained constant for the last four years owing to standardisation. This was a healthy trend, particularly as the cost of material and labour had risen substantially in the last four years. Paragraph 28 of the Paper referred to box beams, and Mr Murray understood that there were some problems connected with their use since the contractors had had difficulties in ensuring that the concrete was well placed in the bottom flange. He heard that trouble had been experienced on some contracts where a number of beams had been rejected, although the concrete had been weighed. It was difficult to inspect this unless large box sections were cast and people could enter the void. The speaker asked for the authorS' comments on this. There appeared to be no reference in the Paper to the depth: span ratio, which was a rather important item from the overall bridge and road embankment cost and also from aesthetic considerations. This was one of the things engineers worried about first: what was the depth;span ratio like? If it was I: 20 or less the bridge would look reasonable; if it was low, say, 1:15 or thereabouts, a sluggish-looking structure would result. Some of the deeper M.O.T.-preferred beams produced depth:span ratios of 1:15 or 1:16, or thereabouts. There was mention in the Paper of the development of new designs and the speaker hoped that these would con. centrate on producing very large flange beams that had rela. tively shallow webs, producing depth:span ratios of 1:20 and over - because he was sure that this was a designer's beam. It produced a very low embankment and a bridge that looked much better than a heavy one. Mr Murray hoped the authors would say if that was what was intended. Paragraph 49 referred to the use of Corten steel. The speaker had seen one or two bridges in this material and they had looked awful, especially when one was close to them. For major river crossings or major bridges there was great scope for the use of this steel, because they could not be seen close to; and distance lent attraction to their appearance. He hoped that where a steel bridge was being considered for such a location the Ministry would consider Corten as an alternative. Aluminium parapets were mentioned in Paragraph 52. Mr Murray believed that Lancashire had been one of the first authorities to use these and the first to have an accident on them. Photographs of the accident were to be submitted to the Ministry. In this instance the section of the horizontal rail was an open one - a channel section - and upon impact, when non-horizontal forces were involved, this type of rail would collapse much more quick than one fully enclosed. He added that .Technical Memorandum BE5 referred only to the "Z" of the section and perhaps a torsional stiffness could be included in future amendments of this Memorandum to ensure that a fully closed section of railing was adopted as it would have greater strength to resist impact forces .. He fully agreed with Paragraph 68 of the Paper on the avoidance of monotony. In order to show that there was a variation there had to be two or three standa"rd bridges; then one of a different kind.
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Discussion
DR KERENSKY wished to comment on Mr Murray's remarks. Dr Kerensky did not specially advocate cast in-situ work; he had simply said that at present it was cheaper than factory made precast work. One of the reasons was that a factory must involve heavy overheads, whereas site on-costs were low because the contractor had free use of the land and worked in the open. Cost of transport from factory to site and of handling the heavy units at site could also be considerable. If a contractor ever offered precast units in substitution for the cast ill-situ work he should certainly be let go ahead and pocket half the savings. But said Dr Kerensky it had never yet happened to him, not even at the same price. MR M. G. ALLINSON (Eastern Road Construction Unit) said be had read the Paper with interest and had found in it a wealth of detaiL If he understood Figure I correctly, it said that not very many standard beams over 55ft in span had been used in the bridges analysed in this chart. If that were so then the new range of M beams should be welcomed as an addition to a designer's armoury, especially at the rates quoted by Dr Rowe of 25s. to 27s. per cubic foot. In the speaker's opinion this was a very low rate and he said it would be interesting to see if this rate were substantiated in practice. Figure 1 also contained a lot of bridges of 115ft. and over in span, and Mr Allinson wondered if the authors were considering any standard designs for this sort of span range. Perhaps it was, as Mr Deuce had mentioned in his introduction, that these bridges were relatively narrow and not a lot of beams were involved, even though there were a lot of bridges shown on the chart. Mr Allinson agreed with Dr Rowe in his plea for the standardisation of design to be considered. The Ministry of Transport was doing work on a suite of bridge design programmes, and the speaker asked for guidance to be given on the type of design tool to use for the different types of bridges. Paragraph 24 contained the statement that the design procedures for in-situ reinforced concrete voided slabs were those mentioned in Paragraphs 21 and 23. Mr Allinson believed that the Ministry computer program - the first one in the suite - only covered beams or bridge decks which had a size of void less than half the depth of the slab. He wondered if the authors had arbitrarily fixed a void as one which had a diameter to depth of slab ratio of less than a half. If that was so, their statement was correct, but they had gone on to talk about composite cellular decks. They made the same comment that the computer program sponsored by the Ministry could also cater for this sort of deck design. Mr Allinson did not think it could because of the size of the cell. . He liked the comment in Paragraph 22, which stated that: "The less powerful grillage programmes, whilst more economical in running time, are only appropriate for the analysis of decks which can be accurately simulated by a grillage layout." This was quite true, but he would have thought the composite cellular decks did not accurately simulate grillages, yet this was one of the tools they had been told could be used for this type of deck. Turning to the composite steel and concrete section mentioned in Paragraph 33, and going on to the design section in Paragraph 38, this part of the Paper stated that the Morice and Little method, while not directly applicable to this type of bridge deck, could be used. The speaker presumed that this could only be used when the steel properties were transformed; but there use. to be some dispute about the value or correctness of the transverse moments which came out of a Morice-Little analysis of this sort of deck. He wondered if 'this was still so, or whether further research had decided otherwise. Paragraph 41 mentioned the permitted distribution of HA loading. In the speaker's experience this was not as weIlknown as a Ministry-permitted design rule as the authors
<

perhaps imagined. Some readers of the Paper might be a little surprised to see it slipped in almost as an aside. In the precast beam section, Paragraph 42, reference had been made to deflected tendons. At least one major precast concrete manufacturer had told the speaker that his preference was to debond rather than to deflect tendons. The speaker hoped that the omission of debonding in the Paper did not mean there was some sort of secret embargo in the Ministry's mind on this particular method. Finally, Paragraph 59 mentioned some of the factors which had to be considered when a choice of over or underbridge was being made, but there was no reference to sight lines. In the speaker's recent experience the influence of the sight line criteria was having a great effect on the bridge layouts being proposed by Ministry sub-units and consulting engineers. If slip roads approached very close to a junction, to the main through route, then very wide overbridges or, conversely, very long-span underbridges, had to be provided. Mr Allinson thought therefore that the influence of sight lines on the layout .and choice of type of bridge could well have been mentioned in this Paragraph. MR WALWORK (reading the contribution of Mr J. M. Smith (Lancashire C.c.)) said that Mr Smith regretted that he was unable to be present. As a bridge engineer Mr Smith had had many associations with Mr Holland over the years, and he wished to compliment him, as Head of the Bridges Division of the Ministry of Transport, on the great amount of technical information on bridge design and construction which was now being issued by his Division in the way of Technical Memoranda and directives which were of great value to highway bridge engmeers. He also wished to pay tribute to the friendly co-operation and assistance which local authority bridge engineers had received from the Bridges Division of the Ministry throughout many years. Having had a preview of the draft of the Paper Mr Smith had a few observations to make. Section 9. Costs. He agreed with the authors that it was very difficult to make comparisons of unit prices between one contract and another due to the great variation of pricing. It was currently found that although tenders were being invited from a small list of selected contractors, there was a considerable variation between the lowest and highest tenders. For estimating purposes, it appeared that the mean of the rates from all tenders should be used rather than the rates from the lowest tender. Great difficulty was also experienced in comparing rates for bridge items in different tenders due to some contractors grossly overloading certain preliminary or general items, e.g. setting-out. Section 24. RC voided slabs: The use of polystyrene circular void formers of 20in. diameter on a recent contract had been most satisfactory and no difficulties had been experienced. Section 38, Design: The authors had referred to the Hendry and Jaeger analysis as being suitable for beam and slab decks, without restriction of the angle of skew. This method of analysis, however, was only applicable to torsion-less grillages and as the torsional inertia of the beams and the deck slab should be taken into account the Hendry and Jaeger analysis was not a suitable one. Mr Smith hoped the authors would give their views on this. With regard to the M.O.T./C and C.A. Standard PC Bridge Beams - M. Type (Inverted Tee) mentioned in Section 42, Precast Beams, Mr Smith hoped that these would be adopted nationally and that the types developed by local authorities (e.g. West Riding, Cheshire and Lancashire) would be superseded by the new standard beams. Section 44, Studies Currently in Hand: With regard to motorway overbridges having composite steel decks, Mr Smith
AUGUST 1970

J

Ie

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Discussion
wished to mention that due to the annual growth of motorway. traffic the maintenance painting of steel overbridges carried out on M6 last year had become a much more difficult and dangerous operation. The measures necessary for ensuring the safety of motorway traffic and painting personnel were so great that, in his opinion, only in very special cases should steel overbridges be adopted for new motorways. The use of self-weathering steel would, of course, obviate these difficulties, provided the appearance of such steel for fascia girders was acceptable. The use of permanent shuttering to the underside of composite steel and concrete decks in appropriate cases to eliminate the construction and removal of temporary shuttering, and dispense with joiners, had been resorted to by several contractors, with the approval of the engineer. This had resulted in substantial saving in time. Ribbed steel sheeting and reinforced fibre-glass had been adopted. Section 51, Standardisation: It was to be hoped that the present standard widths of two-lane and three-lane motorways would remain "standard", Mr Smith felt it should be mentioned that since the building of the Preston By-Pass length of M6 the width of motorways had been changed twice and this had prevented standardisation of bridge designs for M6 on subsequent motorways. Nevertheless, there were considerable economic advantages resulting from standardisation of designs and "preferred designs", particularly for motorway bridges. However, for bridges carrying all-purpose roadsand some motorway overbridges - the provision of pipe bays to carry major services presented difficulties in the standardisation of designs. The inner edge beam carrying the pipe bay was usually the critical one for design purposes and its depth would dictate the deck thickness. In general, standardisation of width module for underbridges on all-purpose roads and motorway overbridges was difficult to achieve, having regard to road curvature, sight line considerations and the widths of footways and pipe bays. Section 67, Fonn and Appearance of Bridges: The M.O.T. booklet on 'The Appearance of Bridges" was highly commendable and its recommendations were very useful. He agreed with the authors on the necessity to avoid monotony, resulting from repetitive designs of motorway overbridges. Normally this could be achieved as a result of having to cater for footbridges and occupation bridges in addition to bridges carrying different classes of road over the motorway. He considered there was full justification for facing the wing walls and a short return of the abutments with split block artificial masonry on a few of the motorway over. bridges where amenity value warranted the additional cost. MR B. P. PRITCHARD (W. S. Atkins & Partners) congratulated the authors on their Paper. He was particularly impressed by the histograms and the wealth of information revealed. Being firmly convinced of the benefits of bridge span continuity, he had turned to the information on the 1967-1969 viaducts contained in Table 5, fully expecting to find evidence of similar convictions among his fellow engineers. His apparent complacency was somewhat shaken by the statistics, which had indicated an overwhelming use of multi-span simply supported structures rather than multi-span continuous structures, in the ratio of nearly 6: I in terms of spans. He had been even more surprised to learn that, where the new design/cost studies covered multi-span structures, continuity was included for steel/concrete composite construction but not for decks utilising the new standard PSC beams. Indeed, as Dr Rowe had said, Table 7 appeared to be strictly non-comparable, as depths were given for continuous steel 1 concrete composite as against simply supported PSC beam decks. The recent experience of the speaker's firm indicated the advantages of continuity with both the old standard PCDG beams and the new longer beams. The reductions in depth,
AUGUST 1970

I

•

I
~.

~

bearings, joints and pier and foundation sizes usually showed cost advantage, particularly where differential settlement effects were not oversignificant. Added to this, the bridge appearance benefitted not only from the more slender decks and piers, but from the absence of visible water percolation, which was more likely to occur with simply supported multispan decks, despite recent improvements in deck waterproofing membranes. The reduction in joints with the longer spans also added to running quality and lessened maintenance problems. Several multi-span bridges and viaducts had recently been constructed on the Hendon Urban Motorway using standard or slightly modified PCDO units. Continuity had been obtained by various methods, including in-siru downstand capping beams and in-situ integral capping beams, either reinforced or prestressed transversely. One example, the 800ft long approach viaduct to the Fiveways Corner Flyover, continuous and using PCDO units, had just been completed. His Ministry friends had informed him that the eighteen spans of that structure were, in that instance, omitted from Table 5. Insertion would help to reduce the continuous/ simply supported discrepancy referred to earlier. With regard to the new larger standard beams, a current design proposed for a six-viaduct complex in North-East London, involving 65 spans, used the longest 29m beams to form 32m continuous spans. Continuity for the in-situ slab concrete, surfacing and live load was gained by utilising a 5m wide in-situ concrete integral crosshead containing longitudinal continuity reinforcement and transverse prestressing. The structural depth for 32m spans was 1,350mm which showed considerable advantage over the structural depth of 1,490mm for the 29m simply supported multi -span structures quoted in Table 7. Mr Pritchard asked if the studies currently in hand would be extended to include multi-span continuous systems using the new standard beams besides the multi-span simple supported systems already under consideration? A further point arose, which once more related to continuity. Paragraph 47 of the Paper referred to the use of buried joints under continuous surfacing in accordance with BE.6 for 15 and 25 metre multi-span simply supported structures which used the new standard beams. Table 1 of BE.6 quoted a total range of thermal movement of 5.3mml 10m for this type of bridge resulting in design values of 8mm and 12mm for 15m and 23m spans. However, Table 2 of BE.6 quoted a maximum total longitudinal thermal movement of IOmm for the type of joint used. It therefore appeared that the 23mm span was outside the range of the buried joint and required a gap joint. If shrinkage and residual creep movements were added, it would appear that the 15m spans also required gap joints .. One final point related to the use of Corten steels in bridge design. The speaker recalled a B.C.SA. meeting some years ago where one contributor had spoken of the use of Corten steel and warned of possible rust film shedding in the first few years. This phenomenon had apparently occurred during the spring and shedding had been in large and somewhat weighty chunks. For this reason, it had been thought that structures using Corten should not not be located where any skin shedding would endanger people or vehicles. The speaker therefore asked whether further knowledge of this reported phenomenon had emerged during any recent Ministry investigations. MR A. F. GEE (Mott, Hay and Anderson) started by asking if he might have a little further explanation of one or two paragraphs in a most interesting Paper. He did not understand the reference to falsework in Para. graph 29: as he read it the two forms of construction compared were composite cellular and solid composite, both of which utilised precast units as self-supporting permanent shuttering. Paragraph 43 and Appendix A referred to the expense of modifications to standard units and an earlier speaker, Mr
THE JOURNAL OF THE INSTITUTION OF HIGHWAY ENGINEERS 19

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L

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Discussion
Allinson, had expressed his hopes that the Ministry did not consider debonding as an extravagance. Mr Gee hoped so too and a comparison between Appendix A and a similar Table which appeared in Mr Holland's Paper published in the JOr/mal of the institution of Highway Engineers in July 1967 showed that this item had been deleted. Could it be inferred, therefore, that the Ministry were now happy to accept debonding'l The s~aker said he was glad to see item 8 in the Appendix, because 11was not many years ago that the Ministry required the number, size and exact position of every wire or strand to be shown. Invariably the manufacturer wished to alter this to suit his templates. Even defining the force and eccentricity might be too restrictive unless tolerances were included. He felt the best solution was to specify the maximum and minimum values less of the top and bottom fibre stresses due to prestress alone, after losses. In his introduction, Mr Deuce had said that alternative forms of construction being investigated included transverselystressed precast box beams and Mr Gee wondered whether he was serious. It was his impression that this form of construction had long ago been discarded as uneconomical. There was a lot of "hard-sell' publicity being given to the new M beams, but the speaker did not think they were a very good design. His firm had spent a great deal of time in preparing solutions for various projects using these beams but always seemed to come up against the same problem: the tiny little top flange became overstressed. In a well balanced design the various limiting stresses were reached at approximately the same time but with M beams it was impossible to achieve anything better than a triangular distribution of prestress and the combined effects of the weight of the beam itself and of the in.situ concrete were usually sufficient to stress this tiny top flange up to its limit with nothing left to carry live load. Perhaps Dr. Rowe could tell him where he was going wrong. The speaker asked if the Ministry were going to give further consideration to the use of partial prestressing which offered considerable economies in precast composite construction. He also asked about the Ministry's attitude to two-stage stressing which seemed to him to be ideally suited to precast composite construction where the ability to stress out the effects of the added in-situ concrete enabled savings to be made not only in direct cost 'but more particularly in construction depth. He felt that both these topics merited close investigation more than a resurrection of transverse stressing. Everybody was very surprised to find in-situ concrete cheaper than precasting, but why wasthis.surprising? In theory precasting was marvellous but when you got down to it exactly the same operations were being carried out with the same materials: the formwork had to be made and the use of steel moulds could only he justified if there was considerable repetition which could apply equally welI to in -situ construction: the reinforcement had to be cut, bent and fixed, the" concrete had to be batched and mixed, transported from mixer to forms, placed and vibrated, and the moulds had to be stripped. All this took place under an expensive roof and, as Dr Kerensky had so rightly said, on one's own piece of land instead of, as with in-situ construction, on somebody else's site. Operatives were being paid very nearly the same amount because the unions had got it rigged that way and then, as if all this was not enough, it was necessary to pick up the lump of concrete and move it, not once, but probably two or three times, and often a hundred miles or more! It wasn't really surprising that precasting was usually more expensive. The speaker also felt that the position was exaggerated by the contractors (and he hoped that if there were any contractors present they would take him up on this). Contractors were not very wise before the event. Their prices were based solely on the quantity of materials and the designer got little or no credit at tender stage, when it mattered, for simplicity of design. What really paid off, particularly in bridge design, was minimum material content. There might be a lot of complaining later on and the contractor would be ready with greatly
111 THE JOURNAL OF THE INSTITUTION OF HIGHWAY ENGINEERS

increased rates for a similar design next time, but there was always another contractor available who had not been bitten and who was prepared to price it per cubic yard again. in-situ construction generally resulted in smaller material content because,. as several speakers had said, the structure could be designed more efficiently, loads had to be carried only once and advantage could be taken of full structural continuity if desired which was not often possible with precast construction when continuity for live load was usually the best that could be obtained. For the same reasons, smaller construction depths could generally be achieved, offering a further potential saving in overall cost, All in all, except for the unusual case involving massive repetition, one was almost always forced to use in - situ con. struction whenever it was possible, and this applied to all overbridges and many underbridges on new roads, if one was able honestly to substantiate the most economic solution. Paragraphs 72 to 74 of the Paper referred to complete standard designs churned out at the press of a button. The speaker thought this sounded a marvellous idea and he felt sure it was not far off, but he was equally sure the applications would be limited to projects handled by sub-units and local authorities. Consultants like himself would still continue to earn their keep from the unusual, non-standard and one-off jobs. Paragraph 75 of the paper filled him with horror. It made him think of Henry Ford: "You can have any edge detail you like so long as it is ours:' Paragraphs 67 to 70 he had found most refreshing because he had always felt the problem of overbridges on motorways and new trunk roads to be worthy of special attention. Unless one traversed the countryside in a series of semi-circles one did not pass under a number of consecutive underbridges, but driving along a motorway the repetitive impact of the overbridges was a major aesthetic problem and the question of monotony an important factor. In this context, an earlier speaker, Me. Murray, had suggested that perhaps every two or three standard overbridges should be relieved by one nonstandard bridge, on the theory, no doubt, that it was lovely when they stopped! Paragraph 2 of the Paper stated that an average of 25 per cent of the total cost of a contract was probably accounted for by the structures. Elsewhere reference had been made to the fact that overbridges were generally considerably less expensive than underbridges. Mr Gee said he would be interested to know the proportion but it seemed reasonable from this to assume that overbridges might account for about 10 per cent of the total cost of a contract. On this basis, an additional 10 per cent on the cost of overbridges spent on improving their appearance amounted to only I per cent on the contract, which was well within the Ministry's yardstick for architectural treatment and finishes. Mr Gee felt that this extra money, if available, should not be spent on applied treatment and finishes but on better basic designs, a point which an earlier speaker, Mr Smith, had emphasised. The speaker then showed some slides of overbridges to illustrate his point that aesthetic elegance could best be achieved through the form of the structure and that this was not compatible with standard designs. MR J. O. THOMPSON (Leonard Fairclough Limited) said he would deal with two items. The first concerned Dr Kerensky's point about precast units versus in-siru construction. As contractors they were happy to be pouring decks in-situ on M5 fOf Dr Kerensky whilst they had converted certain of Mr Murray's in-situ bridge decks into precast un;ts. It was difficult to take the cost of a bridge deck out of the context of the whole contract. Where there was a particular bridge which could not be started until quite late it needed to be constructed very quickly to fit into the programme. There were, therefore, other considerations besides the basic cost of the material going into the deck. One of the considerations in the case Mr Murray had in.
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Discussion
stanced was that the groufid over which the bridge was being constructed was very p.oor. For in-situ construction a lot of money would have had to be spent to provide a stable base for the support works. The bridge was also 400ft long and narrow and access through it was required for muck shifting, so it would have been necessary to have an access tunnel through the support works. It was easier for the speaker's firm to take this sort of action by reason of having their own precasting factory. The second point concerned debonding as against deflecting. At their precasting factory they had designed the bed particularly for deflected tendon .bridge beams. With the particular system which they used it was cheaper to deflect than debond strands, this might not be the case where an existing bed and more elaborate deflecting mechanism were being used. One trouble with debonding was that in a shallow bottom flange. as in the M type beam the debonding material interfered without flow of the concrete to the edge of the flanges. MR. G. B. COLBRIDGE (British Steel Corporatign) said he wished to take up one or two of the points which had been raised on the use of "weathering", including Corten steel. He agreed with Mr Holland that in this case beauty was in the eye of the beholder. All the indications were, from its wide use in America. that it was aesthetically acceptable and the Michigan State Highway Commission were designing 180 bridges in this medium. From the objective point of view, there was no reason why they should not look quite attractive. As far as economics were concerned. the bridges were undoubtedly the cheapest solution to the maintenance problem because. broadly speaking, the total cost of using a weathering steel was rather less than that of even the less sophisticated conventional initial surface protection systems. At the same time, the cost of the repainting cycles was removed. There was a test site in Glasgow where the moulting phenomenon had 'been noted. The reasons for this continuous moulting were at the moment somewhat obscure, but it was certainly not an experience which was being repeated on other sites. After the initial oxide formation period of about 2-3 years, a basically stable surface should be achieved and this could be noted at several sites in the United Kingdom. It was important to note that there were certain circumstances where weathering steels were contra-indicated and, generally speaking. a combination of an industrial and wet climate was not desirable from the point of view of optimum performance. The Corporation was producing shortly an advisory folder on the use of weathering steel in bridgework, including the extended table of properties which, later in ]970. would be included in an addendum to BS,4360, already through the B.S.!. Committee concerned. MR L. R, WADDINGTON (British Rail, Southern Region), referred to a Paper given fifteen years ago by Mr Holland.'" This had compared bridge decks of prestressed rectangular units with compositely-constructed decks and had brought out the very marked saving in construction depth in favour of rectangular units. Inspired by this the Southern Railway had developed a range of standard pre-tensioned road bridge beams for spans of 20 to 80 feet. .These were of rectangular shape, placed side by side and jointed with reinforced concrete to fonn shear-connected decks on the lines indicated in Figure 6(c) but being of solid section they achieved a shallower depth at mid-span than could be attained with inverted tee-beams or box beams. In fact the span: depth ratio was 25.5 for all spans above 27ft. They were also of a hog-backed shape which, for the longer spans, reduced the depth at the end to about two.thirds of that at midspan and saved prestressing. Prestressing was also reduced by debonding and/or deflecting some strands. Such designs which entailed a minimum of site work had proved especially useful in the renewal of shallow decks to bridges with steep approaches over the railway, as they eliminated or minimised the need for expensive road regrading works on the approaches. It was perhaps labouring the obvious to say that these savings were contributed to by the extra shallowness of the beams towards their ends. They had been used extensively to meet the Region's bridge-guard strengthening programme. The design was based on HA loading and checked for a ] 20 ton vehicle on a 26ft wide deck with 5ft wide ful1y-Ioaded foot. paths, using Dr. Spindel's distribution analysis techniques, referred to in Paragraph 28 of the Paper. The same design served for wider bridges and where edge stiffening was required extra concrete could be bonded on after transfer. At parapets, concrete added to provide a level bed for the brickwork was arranged to overhang the beam-top, thus providing a pleasing, curved shadow line. For transverse connection the reinforcement was designed to control rotation at the worst joint under the load and this was investigated for various combinations of width of beam and of deck. Two standard widths of beam were then decided one: of 20in going width (the same as the PCDG inverted tees) covering most spans and the other of 31in, for the span range 25ft to 45ft. Standardised reinforcement was then chosen to cover the worst cases. For carrying 37t or 45 units of HB loading the same stan- . dard beams could nonnally be used, provided 3in minimum overlay of concrete was bonded on at site, or better, if extra depth was obtained by curtailing beams designed for a longer span. In the case of a bridge with a very sharp skew, having 72ft span beams, a grillage computer analysis with] 50 ton vehicle loading indicated unacceptably high transverse shears and hogging rotations. particularly near the obtuse corners. As a result. the design was modified to include shallower beams, but with a top situ slab which included transverse steel. Reruns with different transverse bending stiffnesses soon produced moments which were compatible with the steel provided. It was thought that the beams described could have a place in the wider national context and might even justify inclusion in the current pricing studies, although it was appreciated that in the motorway and trunk roads context construction depth might not be such a vital factor as it sometimes was with railways. In urban development, however, it was often of crucial importance. THE CHAIRMAN said that it was always very interesting to hear experts talking on their subjects. He thought that al1 would agree that they had heard two real authorities speaking on. the question of small-span bridge design and standardisation. The authors had obviously put a great deal of time and energy into the preparation of their Paper and the discussion it had provoked was a great tribute to its worthiness. The meeting then tenninared,

~ I

I
r
r
I I I

, ,.

* A. D. Holland, Prestressed Units for Short-Span Highway
Bridges. (Proc. ICE, Pt. II, June 1955).

AUGUST 1970

THE JOURNAL Of THE INSTITUTION OF HIGHWAY ENGINEERS

21
-

L

Written Contributions
MR WADDINGTON. Further particulars of British Rail (Southern Region's) standard hog-backed road-over-rail bridge decks are given in the following table. This shows, allocated to span-ranges, the number of bridge decks built (or about to be built), their total area, and their average cost (based on lowest tenders) per sq. ft. of that area, brought to 1969 prices. and including a rated proportion of the constructor's charges for "preliminaries", "dangerworks", "insurances" and water for works". It also shows, for comparison, sirriilar particulars in respect or' concurrently-built bridge decks using standard GRBfC & C.A. pretensioned inverted tee beams and compares their structural depths. In both cases the items taken into account are those for the structural deck, up to and including the water-proofing layer which, in the case of the hog-backed beams, was usually placed directly on top of the precast beams while, for the inverted tees, it was usually three inches above the beam tops. Items for bearings, road screed and surfacing and parapets 'are excluded, For the few decks which did not have a proper water-proofing layer, a representative cost was added. Where bulk supply arrangements for beams operated (i.e. for 77 per cent of the hog-backed beam deck area and for 27 per cent of the inverted tee beam deck area) the cost of the supply and delivery of the beams was added as if it had been itemised in the erection contractor's tender thus putting a share of the "preliminaries" etc on to it. Otherwise, it was felt that the figures would have shown undue advantage to such jobs. In all cases, the spans were simply supported and were for HA loading, with capacity for 30 units HB. In a few cases they were given capacity for 37t or 45 units HB. Manufacturers of the hog-backed beams have included the British Rail Board at Taunton Concrete Works, Wand C French Ltd., Loughton, Essex, Cowley Concrete Co. Ltd., Abingdon, Berkshire, Dowmac (Products) Ltd., Tallington, Lincolnshire and Anglian Building Products Ltd., Lenwade, Norfolk. From the Table it will be seen that for spans between 25ft and 50ft, the overall average cost per sq. ft. of inverted tee . beam bridges was 13 per cent less than that of hog-backed beam bridges. However, two very cheap bridges (one of which used bulk-purchase beams) were included among the inverted tee beam type. These were multi-span with many similar beams, accounting respectively for about 7000 and 8000 sq. ft., of deck area, whereas among the hog-backed beam type there was no bridge or deck area exceeding 3,500 sq. ft. If the former are excluded, the percentage in favour of inverted tees drops to an 'insignificant 2 per cent. Thus it seems probable that hogbacked beams could hold their own on cost, even on sites where construction depth is of no consequence, for bridges of comparable size and span. For spans between 50ft and 80ft, the fully standardised hogback design has only recently been completed. The costs shown may reflect some non-standard aspects. It would be in. teresting to know how they compare with those for other forms of construction. MR G. SOMERVILLE (Cement and Concrete Association). There are one or two points in connection with the Paper and the subsequent oral discussion on which I would like some cIa rification. First of all, do I understand correctly from Paragraph 28 and Figure 6c of the Paper that shear key decks can now be designed using articulated plate theory, where the precast units are hollow? Presumably BE 23 is based on Dr Spindel's work on bridges incorporating solid rectangular precast beams; has any account been taken in preparing this Memorandum of the research being carried out by Professor Cusens at the Univercity of Dundee on shear connector decks incorporating hollow precast units? The authors infer in Paragraphs 24 to 28 that the most popu. lar form of construction for the span range 15 to 29m is some form of cellular construction, which may be either completely in-situ or of composite construction. Mr. Allinson raised a point which is not specifically mentioned in the Paper but which requires further clarification. He seemed to think that the Ministry had imposed a restriction on the ratio of depth of void to overall depth that could be used; a maximum value of 0.5 was mentioned. Surely such a restriction, if it exists, is unnecessary. If a computer analysis is used, then, provided an accurate assessment is made of the stiffness parameters, a realistic solution will be obtained irrespective of void configuration; an appropriate computer analysis should automatically

"1

1

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'.1

fj

Bridge Type

Hogbacked

I

Inverted Tee

Hogbacked

Span range feet 25 to 30 30 ,,35 35 ,,40 40 ,,45 45 ,,50 Sum 25to 50 50 to 60 60 ,,70 70 ,,80 Sum 50 to 80

Number of bridge decks

Area of deck (span centres of bearings by overall width) square feet

I

Inverted Tee

Hogbacked

I

Inverted Tee

Average cost (at 1969 prices) £ per square foot 3.14 3.52 3.70 4.50 3.12*
+-~

Average Ratio of midspan structural depths lnv. T Hog- Back 1.38 1.28 1.21 1.24 1.45

9 12 4 1 1 27 3 0 2

18 6 3 3 4 34 0

8,553 12.794 4.790 906 1,315 28,358 9,590

16,455 10,380 5,840 5,230 4,148 42.053

2.72 3.27 2.54 2.86 4.29
+- .....

... t--

3.45 5.25

3.00

1.31

0 0
0

4,920 14,510

+-~

5.72 5.38

AUGUST 1970

5

*District Engineer erected this bridge. His charges may not be strictly comparable.
22 THE JOURNAL OF THE INSTITUTION OF HIGHWAY ENGINEERS

Written Contributions
be able to deal with the effects of shear deformation should these be significant. The question of a limit on the above ratio should only crop up in hand calculations for a simple structure or in the preliminary design of a complex structure, where it might be dilIicult to take shear deformation into account; even then a maximum value of 0.5 would seem to be too low and any such limit should be related to the shape of the voids. Cerfainly it is true to say that shear deformation was insignifi. cant in the large scale concrete model bridge tested by the Cement and Concrete Association to derive design methods. for the M beams when used in the form of construction shown in Figure 6a of the Paper. An in-situ concrete model slab with circular voids and a ratio of void depth of 0.78 is under overall depth test by the Cement and Concrete Association at the present time. I would welcome the authors' comments on these points. Paragraph 46 and Table 7 of the Paper compares the section depth required by different forms of construction for a range of spans. A point worth making here is that the structures represented in Table 7 have been designed for loading configurations that are more severe than those currently required by present Ministry regulations: this highlights even more the comparisons drawn in Paragraph 46, since the previous designs using the modified PCDO beams were based on the current lighter loading requirements. A further point is that these depths can be considerably reduced if the bridge is made continuous for live loading; this is particularly so for shorter spans where the live load moment forms a relatively higher proportion of the total moment. The voided composite slab shown in Figure 6(a) of the Paper is particularly suitable for designing for continuity since it is easy to incorporate the necessary steel to carry the negative moments over the supports in the top slab, and also to provide a positive connection in the compression zone over the supports to prevent any cracking in the support diaphragms due to long term effects (creep, shrinkage etc.). J would also like to make a few brief remarks about the whole concept of standardisation and when precast as distinct from in-situ construction should be used. It was obvious from the verbal discussion to the Paper that the speakers generally felt strongly about this an~ were very much in favour, or very much against, one or other of the forms of construction. This outlook was also apparent in the costing exercise referred to in Paragraph 17 of the Paper, where the prices quoted for any particular structure varied considerably between individual contractors, some preferring to do the job in in-situ construction and some in precast; however there was little difference between the lowest tenders for the two forms of construction in most cases. Since, as is stated in Paragraph 29 of the Paper, no account was taken of the possible need to comply with special requirements of road or rail traffic, this makes the cheapest precast form of construction an attractive viable proposition since precasting will mean that the bridge can then be built quicker and with minimum interference to traffic. As was mentioned during the verbal discussion, there is a need for both forms of construction since either may prove to be the cheaper under a particular set of circumstances. Part of the difficulty with precast construction and the use of standard sections in general is that all too frequently the "standard sections" are not really standard at all since each individual designer has tried to improve on them marginally or to tailor them to meet his own particular design situation. A glance at Appendix A shows that costs can increase rapidly for any non-standard items: consultations between the designer and manufacturer at an early stage about what facilities are available can reduce costs enormously. I sincerely hope that the Ministry of Transport will emphasise that standard beams should be accepted as they are without expensive modifications. There is also scope for further standardisation of such items as secondary reinforcement: do the authors have any plans for incorporating this type of standardisation in their overall general plan? PROFFSSOR. F. SAWKO (University of Liverpool). May
AUGUST 1970

I congratulate the authors on an excellent and timely Paper which contains a wealth of information for all involved with design and construction of small span bridges. As a research worker and consultant in the field of bridge design my comments will be restricted to various design approaches and analyses referred to in the Paper. It was most gratifying to read in Paragraph 21 that the grillage computer method is at long last officially approved by the Ministry for analysis of bridge decks. This I find personally gratifying because of the lonely battle which J have fought for the past 10 years or so in trying to convince engineers of the attractions of the grillage approach. Undoubtedly a great contribution to this final success has been made by the West Riding County Council (Bridges Section), in which M r Deuce has actively worked before his present appointment, and which was one of the first bodies to make extensive use of my grillage programs for design of several bridges on the AstonSheffield.Leeds section of the Ml Motorway. The approval of this method is. in my opinion, long overdue and one has to bear in mind that even as late as 1967, at a discussion on design of prestressed concrete bridges, the method was not officially recognised by the Ministry. Paragraph 22 refers to the grillage method as "less powerful" because of difficulties with bridge geometry. In my experience of analysis of dozens of bridge structures using this method, I have not yet come across a bridge geometry which could not be satisfactorily tackled by the grillage approach. The most complicated geometry is probably presented by a slab on a number of randomly spaced supports, such as the Cumberland Basin Scheme slab. A model of this structure was tested by the Cement and Concrete Association which also investigated various methods of analysis of this complex problem including grid analysis. Their results are presented in Figure I and they demonstrate that even using a relatively coarse grid for a highly complex structure a remarkable degree of accuracy is obtained. The great advantage of the grillage approach over the "more powerful" finite element method is the fact that equilibrium is automatically satisfied at every joint. I do not doubt, therefore, that for a vast majority of cases the grillage approach will be the accepted standard method for a great many years to come. I trust Messrs Holland and Deuce will forgive my pursuing my present hobby-horse, which is the analysis of cellular decks and cored slabs. This subject has interested me greatly during the last five years, during which time I have proposed various approaches (1) - (6) for the analysis of these structures. I realised a long time ago that the Morice and Little approach was not applicable to cellular bridges where transverse diaphragms were absent and J have emphasised this point many times in technical literature (1)_(5). also concluded that the full three I dimensional finite element analysis of multi-cell bridges would be impracticable with the present day size of computers and this has invariably led me to seek various approximations with a varying degree of accuracy and success. The first approximation was the grillage analysis(l) where the transverse structural medium is represented by an equivalent beam possessing shear as well as bending stiffness. This seems to give a very acceptable degree of accuracy for multicell structures as indicated in Figures 2-4 and has been employed in the analysis of a considerable number of cellular bridges with a high degree of success. It is expected to give even more accurate results with a greater number of cells. For cellular bridges with a small number of cells the method gives good accuracy away from the point loading but under - estimates values immediately under the concentrated loading (Figure 3). The reason for this is probably the assumption of uniform flange stresses in the grillage approximations. In order to cater for this contingency a modified finite element approach has been developed(5) which leads to a linear stress distribution in the top and bottom flanges of a cellular deck and still retains the shear deformation medium for the transverse action of the bridge. A final comment on what is invariably only marginally relevant to the Paper - the design of spine beam bridges.
THE JOURNAL OF THE INSTITUTION OF HIGHWAY ENGINEERS .13

Written Contributions

f:

Figure I (left) Cumberfand Basin Slab - comparison of expc:rimental and gri//age transverse stresses.

Figure 2 (below left), Derails of cel/ldar decks and' grilfage simulation Figure 3 Chelaw centre). Longiwdinal and transverse lIIoment comparison for three cell decks. Figure 4 (below right). Defiexion comparison for six cell deck. and longitudinal moment

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21

THE JOURNAL OF THE INSTTTUnON OF HIGHW .... ENGINEERS y

AUGUST

1970

Written Contributions
The authors' tables and charts indicate that several spine beam bridges have already been designe{l and constructed and it would be interesting to have the authors' comments on approved methods of analysis for this type of structure. I feel that the three dimensional finite element analysis(7) covers all the important effects which are likely to be present in a spine beam type of bridge. The analysis is at present relatively expensive but with larger computers the price invariably comes down. I would be most interested to have the authors' comments on this approach. References (I) Recent Developments in the analysis of Steel Bridges using Electronic Computers. F. Sawko, British Canst. Steelwork Assoc. Conf., London July 1968. (2) Bow Improvement. Discussion by F. Sawka, Inst. Struct. Engineers, July 1968, Yol. 46, p. 204. (3) Brent Cross Flyover, London. Discussion by F. Sawko, Proc. Inst. Civil Engineers, Yol. 41, Nov. 1968, pp. 560-562. (4) Slab Bridges with Arbitrary Shape and Support Condi. rions: A General Method of Analysis Based on Finite Elements. Discussion by F. Sawko, Proc. Inst. Civil Engineers, Vol. 41, Dec. 1968, pp. 813-815. (5) The Analysis of Multi Cell Bridges without Transverse Diaphragms. F. Sawka and R. J. Cope, Structural Engineer, Vol. 47, No. 11, November 1969, pp. 455-460. (6) The Analysis of Cellular Bridges without Tran:;verse Diaphragli1S. G. Harris, Ph.D. Thesis, Liverpool, 1970. (7) Analysis of Spine Beam Bridges using Finite Elements. F. Sawka and R.I. Cope, Civ.Eng. & Pub. Wks. Review, Feb. 1970, pp. 146-7. lJas been suggested that for greater skew angles the same parameters should be -used with other accepted methods of analysis. The following summary of results obtained for a right bridge deck shows a variation which is in our opinion outsidc' acceptable 1imits:-

Max. longitudinal Moments 1. M & L load Distribution Analysis 2. Grillage Analysis 3. M.O.T. Finite Element Program BAPS Kips h/ft 164.7 183.0 129.0

Max. Transverse Moments Kips ftlft 15.9 8.3 14.3

MR K. SRISKANDAN (Midland Road Constructon Unit). The choice between precast and in-situ construction has provoked considerable discussion following Mr Holland's reference to the cost study carried out by him in 1967.(l} These cost studies can only be taken as a guide, and in the 40ft span case the differences in cost are so marginal that neither form of construction can be claimed to be cheaper than the other. Under these circumstances I would think that the precast - prestressed construction - would have the edge because of its greater durability. It is. however. gratifying to see a sufficient body of opinion for reinforced concrete because this maintains a healthy competition between these two forms of construction. In the 60ft spans investigated by Mr Holland the precast beams that were used were extensions of the PCDG Beams, which had been developed only for spans up to 50ft and were not the most efficient design for the higher span. Studies carried out by Cheshire County Counci](2) have shown that a precast beam designed for the higher span range produces a deck which is slightly cheaper than the voided R.C. Slab which came out as the cheapest in Mr Holland's study. Jt would be interesting to see how the new beam turns out in the costing exercise which is being carried out now. In Paragraph 41 the authors have stated that adding the local wheel load moments derived by Westergaard analysis and the moments arising from transverse distribution of load between beams is excessive. It is not very clear what work has been carried out to enable the authors to make this statement. 'I would be grateful for more details of this. The authors have, in Paragraph 42, drawn attention to the new M type beams (Inverted T beams for use in the 15 to 29m span ranges) which have been promulgated recently. In the Midland RCV, we have started designing bridge decks using these beams, and it is worth recording here some of the problems we have come across. (a) Analysis of Voided Composite J)ed(s [authors' Figure 6(a)] In the information that has been released so far, information is given on the calculation of parameters to be 'used with the Morice & Little load distribution analysis. This method of analysis is only suitable for skew angles of 200 or less. It
AUGUST 1970

As bridges over 200 make up approxima~ely 40 per cent of all the normal under and over bridges it is important that an early answer is found to this problem which we have passed over to the C & CA and M.OT. Headquarters. (b) Full scale drawings that have been produced have. shown that tendons positioned in the bottom flanges of the beams cannot be deflected without fouling one or sometimes two of the holes for transverse bars. Therefore, if transverse reinforcement is to be provided, the tendons to be deflected will have to be positioned above the holes through the webs. On the other hand if it were decided to debond at the end to satisfy end stress conditions, again, some tendons will have to be positioned above the holes through the webs. In the whole range of the M beams these tendons positioned above the transverse holes will be above the level of the neutral axis and will, therefore, be uneconomical. If, however, the contiguous beam deck (Figure 6b) was adopted, the tendons could be positioned in the bottom flange where they are most efficient and at the ends some of the tendons could be deflected without any difficulty, and if required, others could be debonded. This would result in a more economic use of prestress over the type of deck. I would like to know from the designers whether they came across these problems in the designs they have carried out for the cost exercise. (c) The authors have stated that the M beams require the use of deflected tendons for the upper range of span. Some calculations that we have carried out have shown that the effects of shear are worse in the lower span range than in the upper span range. The Table overleaf gives some examples of the shear stresses produced and the residual compression required to maintain the principal tension under certain prescribed limits for various sizes of the M beams. The shear forces used to calculate the stresses (See Table) have been calculated in a semi-empirical manner - but it is considered that even if these were calculated by more accurate methods the same conditions will apply and in the . larger span range the principal tensile stresses can be reduced to acceptable limits with only a small compressive stress, while in the lower span range a large compressive stress, or a compressive stress together with deflected tendons, is required to limit the principal tension to acceptable limits. In Paragraph 47 the authors have stated that "for the simply supported multispan bridges the surfacing is continuous across the whole bridge. buried joints over the intermediate supports being provided ..... ". The spans referred to are 15m, 23m, and 29m. If one was to follow the rules given in Technical Memorandum BE6, buried joints should not be used at the expansion end of the 23m and 29m spans. I would like to be assured by the authors that the provision of these joints was merely for the purpose of this costing exercise and does not in any way give a licence for contravening the rules of the Technical Memorandum.
THE JOURNAL OF THE INSTITUTION OF HIGHWAY ENGINEERS 25

------------------- ...... ------------------------------.--;l •
'J-

If

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Written Contributions
HA loading inc. permanent SPAN BEAM No. Shear Stress
q

loads

HB loading inc. permanent Shear Stress
q

loads

N/mm2

Direct Compressive Stress f(d) (N/mm2) to reduce principal tensile stress to ft 1.206 N/mm2 1.5ft 1.805 N/mm2 2.08 2.05 1.82 2.0ft 2.412 N/mm2 0.49 0.48 0.30

N/mm2

Direct Compressive Stress f(d) N/mm2 to reduce principal tensile stress to ft 1.51 N/mm2 1.5ft 2.26 N/mm2 4.71 4.34 3.81 2.0ft 3.02 N/mm2 2.20 1.92 1.53

M1 17.52 M. M2 M3

2.65 2.64 2.56

4.61 4.60 4.21

3.96 3.86 3.71

8.93 8.38 7.54

M4 22.10 M M5 M6

2.28 2.34 2.34

3.12 3.32 3.30

1.08 1.22 1.20

-

3.15 3.14 3.10

5.03 5.05 4.87

2.11 2.13 2.00

0.25 0.26 0.17

-

M7 M8 26.70 M M9 M10

2.02 2.17 2.18 2.35

2.18 2.68 2.72 3.37

0.45 0.79 0.81 1.25

-

2.60 2.72 2.71 2.86

2.96 3.40 3.36 3.94

0.72 1.02 0.99 1.38

-

,

All the above stresses refer to the section at the junction between the web and the top flange. Conditions at the neutral axis have not been investigated. References
(I) (2) A. D. Holland the Institution R. J. Bridle, - Present Day Bridge Design Journal of of Highway Engineers - July 1967. A. H. Friston and C. Stone - Bridge Sfandardisafion in Cheshire Journal of the Institution of Highway Engineers - January 1968. which the cost was drawn; for instance a viaduct with decks composed of -beams supported on discrete slender columns, i.e. without capping beam, will be much more costly to erect than one on a traditional slab pier. But this additional erection charge is a consequence not of the deck design but of the

pier form.
MR W. T. F. AUSTIN (Freeman Fox & Partners) fully supported the authors' policy of making available a good range of standard designs of bridges for use when appropriate. He did hope, however, that this range would include in-situ concrete designs. He did not share other speakers' bewilderment that hybrid designs often did not compete in cost with straightforward in-situ concrete bridges; indeed he could quite understand why so much effort was needed in order totry to make them competitive. One only had to consider the number of separate operations involved in various places. One of these, transport of prefabricated units to site, often for distances of 100 miles or more along cross-country routes, also contained a hidden additional cost - delays caused to traffic. In addition, the sub-structure was often simplified where the deck was in-situ. These considerations were not merely academic theorising, they were borne out in practice; the authors had shown that in-situ designs were often cheaper. Quite a number of contractors preferred them in many locations, -believing that problems of site labour were no more difficult to overcome than the problems inherent in many hybrid designs. Tn spite of their inherent economy, in-situ designs would often benefit from standardisation, particularly in the use of standard prefabricated forms for sub-structure as well a~ decks and, above all, for edge details. Once labour became
AUGUST 1970

MR W. R. VARLEY (North Eastern Road Construction Unit) The authors are to be congratulated on the very wide scope of their Paper and also that, for a review which is derived from investigation of statistics, they have presented in the figures and tables the detailed information which forms the basis of their review, and have not expected readers to be satisfied with abbreviated and unsupported information. Unfortunately the more information provided the more one seeks and in relation to Paragraph 2 I would ask the authors if there has been any change in the ratio of structural cost to highway cost over the years that are under review, 1965 to 19697 It would be interesting to see if, after correction for the number and deck area of structures, the proportion of expenditure on structures was rising or falling. Tn Table 3 it is apparent that only in simply supported overbridges does the number of steel bridges achieve parity with the PSC beams, but in viaduct spans (Table 5) the standard steel beam is completely dominant. From -an inspection of Figure 5 however it appears that this dominance may be due to one very large scheme. It is hoped that the new "Method of Measurement for Road and Bridge Works" which the Ministry have published will achieve the object described in Paragraphs 14 and 15. However even under the new Method group costability will be misleading if taken without any consideration of the structure from
16 THE JOURNAL OF THE INSTITUTION OF HIGHWAY ENGINEERS

r~
I

Written Contributions.
familiar with them productivity should be increased. This had been proved on the French motorways where standard in-situ designs had been included in the range and were probably the most popular of them. The French had a system of national standard drawings in which dimensions, bar spacings etc. were given codes instead of specific numbers and were read in conjunction with computer print-outs for each specific bridge. Thus the need for detail drawings was often avoided for each bridge. The general arrangements were derived from a design manual giving design rules and charts. The resulting bridges were often of quite pleasant appearance. In answer to Mr Holland's query concerning the preference for computer programs or of design charts derived from them, M r Austin preferred the charts where the preparation of these was economically justified. As the authors had pointed out, there were literally hundreds of possible alternative combinations of width. span, skew, loading etc. and it would not be economical 10 have a computer grinding out the exact answer to all these in order to produce charts if only say 100 were ever likely to be used in practice. However, as the authors had pointed out, graphical interpolation would be sufficiently accurate for practical purposes. Mr Austin did not favour the use of simple spans in multispan bridges and was surprised at the number in the sample considered by the authors. Did this sample include considerable lengths of road in areas subject to mining subsidence? His objection to simple spans was based on preventing leakage at deck joints, unevenness of riding surfaces at deck joints, awkward details at pier tops and lack of economy. It was noticeable that most of the simple spans in multi-span bridges were of the prefabricated varieties. Mr Austin's firm had not found universal beams to be economic in C9mposite bridges. Asymmetric made-up girders at about IIft centres, with an 8tin R.C. slab were generally cheaper. He was pleased to see that the Ministry of Transport were now thinking in terms of 10 to 12ft stringer spacings with diaphragms omitted which should obviate some of the manifestly uneconomic designs which had been seen with closely spaced stringers and large numbers of diaphragms. Some of these designs almost made one think that the designer, having used a grid program in the computer, had then replaced every link in the grid with a steel member. In' a Paper a year or so back at a BCSA Conference a member of the Ministry of Transport team had suggested, in relation to composite bridges. the use of universal beams sent straight from mill to site, thus avoiding shop overheads. Shear connectors were to be site attached by stud welding. The advantage of such a system would be that fabricating shop overheads would not be incurred. A disadvantage would be that corrosion protection would have to be site applied. He the authors any knowledge of such a procedure being tried out, particularly in relation to Corten steel where corrosion protection in the shops would be unnecessary? If it had been trie(' out had any economies resulted? The Paper refers to savings in design costs. Although these are" very desirable, they should not be outweighed by loss of" economy in the resulting bridge. MR M. J. McPARTLAND (Eastern Road Construction Unit) If certain small span bridges are going to be standardised I feel that they should be equated to a standard design procedure. This question of standardisation of design was asked by Mr. Allinson but it did not. in my opinion, get the response I would have expected from the audience. With the introduction of the finite element technique for slab bridge decks quickly gaining ground in many offices, it would seem that in a short space of time more sophisticated elements in programmes will cater for a variety of decks. It is hoped that this will set a pattern for design as well as achieving efficiency and economics. With reference to the multi-cell shear key deck mentioned in Paragraph 28 I should think that this type of deck would have good lateral load distribution qualities, as there must be interaction afforded by the keys on each neighbouring cell. I therefore agree with Dr Rowe's comments on this point. MR E. W. H. GIFFORD (E. W. H. Gifford and Partners). I would like to support Dr Kerensky's assertion that there is no mystery in the lower cost of in-situ construction by virtue of reduced overheads on site by comparison with precast works. To this can be added, costs of transport, of cranes, and of duplicate supervision of contractor, manufacturer and engineer. These large items can only. be offset by economies of true flow line mass-production, which," by the nature of the market, is not possible. There is a parallel in the prefabricated domestic building market where for many years many people insisted, against all evidence, that factory production must be cheaper than in-situ methods. Although this market gave much better possibilities of quantity production than bridge decks, on-site methods have proved, in general, to be cheaper. From the Paper and the discussion it would seem that this basic cheapness is accepted by the Ministry and indeed is borne out by their studies reported in 1967. In passing it should be noted that the in-siru methods were applied in this study 'to reinforced concrete decks only, presumably, because it was thought that the spans of 12m and 18m were too short for post- tensioning. Would the authors explain why, in the light of the general economic superiority of in-situ concrete, this material has not been included in their current study for spans up to 28m? In comparing method, with method it is vital to consider complete decks and not discrete strips. In-situ construction has advantages in cantilever footway construction, in case of pro. vision for continuity and for transverse distribution and optimum placing of skew bridge reinforcement, all of which may considerably influence the cost of a complete deck. "

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AUGUST 1970

THE JOURNAL Of THE INSTITUTION OF HIGHWAY ENGINEERS

27

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Authors' Replies
Shear Key Decks Dr Rowe has not unnaturally taken "functional efficiency" as synonymous with "distribution efficiency", whereas "cost effectiveness" would express the authors' meaning better. The slide which showed the shear key deck as having a shallower construction depth than the voided slab, also showed that it cost on average 17 per cent or II s per sq. ft more. The figures quoted by Mr Waddington are very useful and confirm that the shear key decks are more expensive than the inverted tees but that in particular circumstances they may still be economical because of the saving in construction depth .. Pending the" outcome of Professor Cusens' research work it is considered, in relation to Mr SomerVille's question, that the articulated plate theory can only be applied to hollow precast units when an adequate number of transverse diaphragms (say lo-I5ft centres) is used. Combined Stresses Mr Deuce stated in his introduCtion that any, saving resulting from current research into co-existent overall and local transverse bending stresses would improve thlf competitiveness of both concrete and steel beams and slab decks. The attempt to rationalise the analysis of co-existent stresses does not stem from the CP II7 rules. As stated .in the Paper summation of the effects by manual methods have been found to give higher values than those derived by various forms of computer analysis. Until methods of simulating cracked slabs in analysis are available an increase in permissible local stresses as suggested by Dr Rowe (following appropriate research) will probably be the most expedient way in which to deal with the problem. In-situ Construction The authors accept that in-situ construction both in the form of solid slabs and cellular slabs can and does prove to be economical in many instances. Subject to the limitations pointed out by Mr Thompson the indications are, where site conditions and programme requirements are not paramount, that in-situ construction can be the more economic. In the st~ndardisation exercise. particular attention has been paid to precast work as having the most to gain from such treatment. Nevertheless the authors agree that standardisation of in-situ construction should not be neglected and they hope, resources permitting, to develop standardised design in-situ construction at an early date. Continuous Span Construction A common construction depth of approximately 1/20 was adopted for the simply supported and continuous designs for both the composite voided slab and the composite steel and concrete decks so as to enable a direct cost comparison to be made between simply supported and continuous construction. Advantage was taken of continuity to reduce the prestress in the continuous concrete designs and the. steel flanges 'in the composite designs. In both media the studies were based on the beams being simply supported for self weight and that of the deck slab and continuous for superimposed dead load and live load. It would of course be normal in actual designs to take advantage of continuity to reduce the construction depth as suggested by Dr Rowe and others. Comp'uter Programs for Composite Cellular Decks In Paragraph 22 it was stated that the grillage programs are only applicable to decks which can be accurately simulated by a grillage layout. This is not to say, necessarily, that the deck has to approximate to a grillage in apparent layout. Although Professor Sawko in his contribution suggests that the range of applicability is wide the authors consider that this whole question is dependent upon a high degree of expertise based on the results of research work and that engineers would be ill-advised to use any computer programs
28 THE JOURNAL OF THE INSTITUTION_OF HIGHWAY ENGINEERS

without first bei~g convinced by an appropriate authority of its ,applicability in all respects to the problem in question. The authors are grateful to Professor Sawko for the interesting information which he submitted with his contribution. Debonding The authors would' like to make it clear that it was not intended to suggest in any way in Paragraph 42 that there was to be an embargo on the debonding of prestressing tendons at the ends of pre-tensioned beams. Where a factory is set up to deflect tendons as a matter of course it is likely, as Mr Thompson said, that it will be cheaper for the manufacturer concerned to deflect tendons rather than to debond them. Mr Sriskandan has suggested that. if transverse reinforcement is provided, some tendons will have to be positioned above the holes and that these will be uneconomical, but the authors consider that, provided the correct eccentricity for total force is maintained, it is no less economical to space the tendons over the depth of the beam than to concentrate them at a particular level and that there are advantages in doing the former. It is only when the spacing of the tendons over the depth prevents the desired. eccentricity being obtained, that economy would be lost, but a resort to debonding or deflection can obviate this. Shear force considerations may indicate the adoption of deflected tendons for the smaller section beams if used at span depth ratios of 20/1 or more hence the inference that designs based exclusively on the use of straight tendons whether debonded or otherwise may not in fact attain an overall economic advantage. It is inevitable that deflected tendons will foul transverse reinforcement holes. of the voided composite inverted tee beams and that the transverse holes will have to be omitted at these points. It is considered that the resulting interrup. tion to the spacing of the transverse reinforcement can be ignored for analysis purposes but that the displaced bars must be placed, at appropriate centres, in the adjacent holes. M Beams The authors question the prices quoted by Dr Rowe for the M beams, as those returned by 'beam manufacturers in connection with the costing exercise indicate a somewhat higher rate. If this is borne out in practice it could seriously affect the competitiveness of precast concrete with that of both in-situ construction and composite steel and concrete construction .. With reference to Mr Gee's remarks about the inadequacy of the top flange of the M beam the authors would state that when using an overall span to depth ratio for the deck of 20(1 the very considerable number of calculations performed on these beams during their development and during the studies have not at any time led to the top flange being critical. The suggestion has been made elsewhere that the moulds for the M3 and M6 beams should be deep enough for another 80mm module to be added to the top flange thus providing an overlap with M4 and M7 beams respectively. This suggestion is to be included in the booklet on the M beams to be published shortly and beam manufacturers would be well advised to make provision accordingly when manufacturing the standard moulds. The Ministry also intends to discourage departures from the standard beams now promulgated and will endeavour to standardise details such as the secondary reinforcement as suggested by Mr Somerville. Buried Joints Mr Pritchard's and Mr Sriskandan's remarks pre-suppose that the expansion of individual simply supported spans is to be taken at the end of each span. The authors stated in Paragraph 47 that buried joints, in accordance with Technical Memorandum BE6, are to be provided over intermediate supports on the basis that longitudinal movement due to temperature, creep and shrinkage will be accommodated at
AUGUST 1~70

I~

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c.

"

Authors' Replies
either or both of the ends of ~he bridge. Thus the intermediate buried joints -would only have to accommodate rotational movements and would not thereby be distressed. Corten A number of speakers had referred to the maintenance problems associated with protective systems to steelwork. More than a dozen bridges using Corten were planned, under construction, or completed in England and Scotland and its use is being appraised by the Ministry. It was now being widely used in the United States and Canada. Me CoIbridge had commented on Mr Pritchard's query about moulting. The Corporation's advisory folder on the use of weathering steel would be awaited with interest. Regarding Dr Rowe's further queries, circumstances can vary so widely that it is impossible to generalise as to the influence of construction depth on total cost. The added cost for 12in added depth of a 40ft wide overbridge could be £1.200-£2,500 or more. The rate per square foot of deck will depend upon the span. Paragraph 65 does not say nor does Figure 8c purport to show the relative costs of composite steel and concrete bridges as a function of skew. The order of increase in cost is plotted against increase in skew and being imprecise is considered to be roughly applicable to both forms of construction. In reply to the points raised by Mr Murray, the placing of concrete in the bottom flange of box beams has been a problem in the past and has led to the inadvertent creation of voids and the flotation of the core moulds. Most manufacturers have developed methods of overcoming these problems and the authors accept box beams as a viable form of construction. It is intended that the M beams should be used with a l60mm in-situ sla'b having effective depth over the top of the beam of 130mm. This results in an overall span to depth ratio of approximately 20: I when the beams are used at the limit of their span and in the region of 18.5:1 at the lower end of the range to which they are applicable. The authors are not clear how Mr Murray arrived at his ratios of about I: 15 or 16 as, although the use of the M beams in contiguous slab construction results in a deeper deck even at the lower. more critical end of the range, span to depth ratios of 17.5:1 should be attainable and therefore meet his requirement for a "designers beam". There is a limit to the reduction of construction depth which can be achieved and the authors feel that the beam proportions selected. enable a reasonable span depth ratio to be chosen. If an attempt is made to use the beams at span depth ratios greater than about 20: 1 it is possible that there will be difficulty in meeting the shear requirements as has been pointed out by Mr Sriskandan. The authors thank Mr Murray for his suggestion that a torsional parameter should be included in the specification for parapet rails. This is a matter which is receiving consideration but it should perhaps be pointed out that even when the rail has buckled due to ,lack of torsional stiffness it is stilI capable of acting as a tensioned bow string and is thus, in spite of its buckled state, able to contain an errant vehicle. A possible alternative is to require a minimum resistance to vertical forces as well as horizontal forces and this is also being considered. Mr Allinson and Mr Somerville both referred to void ratios. A ratio of 0.5 is recognised as being a low limit. Design can be made with a higher ratio provided that shear deformation is taken into account. The authors would wish to avoid making any major change in current recommendations for voids until further experimental justification of methods of calculating the stiffness parameter of voided slabs is available. The authors regret that brevity in Paragraph 23 should have led to any misunderstanding as to the applicability of various types of analysis to different types of deck. The reference to the forms of analysis being generally as stated in Paragraphs 21-23 should not be taken as indicative of any change in policy ::~:,di"g the 'POH"hil;ty o[ compu'", p"gmm, aod ",'Hcular types of construction. The finite element program BECP /1 is essentially for slab deck analysis and would be increasingly in error for cellular decks as the void size increased and wall thickness reduced unless correct stiffness parameters were used and an allowance made for shear deformation. Regarding other points raised by M r Allinson, Poissons ratio is incorporated into the curVes upon which the Morice and Little analysis is based. This has the effect that the analysis is inappropriate for decks having a structural steel transverse medium. It has no appreciable effect on decks formed from longittudinal steel girders acting compositely with an in-situ concrete top flange. His point about permitted distribution of HA loading was noted. Early opportunity would be taken to include a reference to this in a forthcoming Technical Memorandum. The authors agree with his remark about the effect of sight lines on bridge layouts and this question is being looked at to see if the effects can be reduced by modifying the present requirements. The authors wished to thank Mr Smith for his kind remarks. With regard to his reference to the use of individual billed rates, these can give very erratic answers and the authors favour the pricing of bridge elements when estimating costs. Though rates vary widely, when the total costs of each element of bridge (substructure, superstructure, etc) are compared these are more uniform. The new method of measure. ment enables the cost of each element to be easily extracted and this should make estimating easier. Until such time as the costability of the standardised nature of the items from the MTMM is recognised even mean unit rates from all tenders are likely to be suspect. The authors agree that the Hendry and Jaeger method of analysis ignores torsion in skew structures. For composite construction, where in any case the torsional beam stiffness is low, comparison with other methods have shown that the maximum longitudinal and transverse moments are high. The method is therefore safe though not particularly economical. Mr Gee's point about Paragraph 29 was accepted. The reference to falsework costs related to the in-situ construction mentioned in Paragraph 24. Regarding partial prestressing, the Ministry intends to review its attitude towards its use in the light of the national code of practice covering the design of concrete bridges when this becomes available. The authors agree the possible benefits to be derived from two-stage stressing. These would be kept in mind but subject to further study they were of the opinion that worthwhile cost benefit was most likely to accrue in major construction. M r Sriskandan had drawn attention to the scatter resulting from the employment of Morice and Little parameters with other accepted methods of analysis. Consideration is being given to this by both the Ministry and the C & CA with a view to issuing guidance on the matter as soon as possible. There may have been disparities in the deck width and loading used in the examples quoted. Regarding Mr Varley's query about changes over the years in the ratio of structural costs to highway costs. the proportions quoted in the Paper are "broad brush" and are bound to vary between samples taken even in the same year. Staff resources considerably in excess of those which could be made available would be needed to give a dependable reply. His point about the influence of pier form on deck erection costs is a valid one and has been duly noted. In reply to Mr Austin, Corten in bridges to date has used fabricated steelwork, making shop work necessary in any event. For non-weathering steel any benefits accruing from the site welding of shear connectors would, as he says, have to be weighed against the disadvantages of applying the protective system on site,"which in our view are over-riding. In conclusion the authors regret that the results of the costing exercise are not yet in a suitable form for incorporation in this reply. It is hoped to publish them in a subsequent issue of the Journal.
THE JOURNAL OF THE INSTITUTION OF HIGHWAY ENGINEERS 29

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31 THE JOURNAL Of THE INsmUTrON OF HIGHWAY ENGINEERS AUGUST 1970

8

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The Analysis and Design of Short Span Skew Highway Bridge Slabs
J. Harrop, Ph.D., B.Sc., M.I.C.E .. and N. J. Smithers, M.Sc., M.I.C.E., M.I.Struct.E.

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N. J. Smithers

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BIOGRAPHIES Dr Harrop graduated at Leeds University and subsequently carried out research on composite action in slab-beam systems for the degree of Ph.D. He has held research fellowships at Princeton University, United States of America and at the University College of Ghana. working on variousslab problems. At the Building Research Station he carried out studies of shrinkage and moisture transferin massconcrete. As Engineer-in-Charge of the research and development section of Taylor Woodrow Construction Ltd., he was mainly engaged on problems associated with prestressed concrete pressure vesselsfor nuclear reactors. Since 1964 Dr Harrop has been a Lecturer in Civil Engineering, initially at Sheffield University and now at Leeds University, his main field of research being slab structures. Mr Smithers attended Lincoln School and subsequently served as an officer in the Royal Navy prior to being articled to the County Surveyor of Lincolnshire (Lindsey) County Council. He graduated in Civil Engineering at Nottingham University, and was involved in highway bridge design and construction in Lincolnshire and later in the West Highlands of Scotland where he was engaged on the reconstruction of General Wade's "Road to the Isles'. More recently the author has worked for Staffordshire County Council as a Team Leader dealing with structural and foundation problems. Work at Leeds University on skew slabs with Dr Harrop was a part requirement for the award of the degreeof M.Sc. in Structural Engineering. Mr Smithers now holds the position of Chief Bridge Engineer with Stirling Maynard and Partners. Consulting Engineers,Peterborough.
AUGUST 1970

SUMMARY

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The Paper examines the moments at .criticaf,.:i?o~nfS in certain simply supported cast in situ skew slabs 'sUbjected to a uniformly distributed loading. DirectionaP'design moments are calculated for skew systems of reinforcement: longitudinal and transverse areas of steel are calculated. Consideration is given to the effect of subsidi/ncein the form of a transverserotational subsidence of one abutment and alternative design solutions to -the solid in -Situ s/;1b areexamined. Throughout, an alternative and simplified form of type HA loading is used which leads to a quicker determination of moments for the purpose of slab comparisons. and it is assumed that edge stiffening clauses are not violated.

NOTATION
area of steel reinforcement (sq. in/f!) concrete working stress (Ib/sq. in.) steel working stress (Ib/sq. in.) longitudinal moment (Ib ft/ft) moment/unit angles width of slab (Ib ft/ft) to the longitudinal direction at right

twisting moment/unit design moment/unit direction (Ib ft/ft) My *

width of slab (Ib ft/ft) width of slab in the longitudinal

design moment/unit width of slab at right angles to the longitudinal direction (Ib ft/ft) design moment/unit width of the slab in a direction degrees to the longitudinal axis.
THE JOURNAL Of THE INSTITUTION OF HIGHWAY ENGINEERS

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33

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The Analysis and Design of Short Span Skew Highway Bridge Slabs
w wm W uniformly modified distributed loading (Ib/sq. ft) distributed loading (Ib/sq. ft) steel,
L6

HA uniformly

knife edge load (tb/ft) angle of the transverse steel to the longitudinal measured anti-clockwise from the longitudinal axis. skew angle of the slab.

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PARAMETERS
Poissons ratio,=0.15 Coefficient

USED IN ANALYSES
Young Modulus=4 of rubber bearings

x 106Ib/sq.in.

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Figure] Details

5H' S q"ar.

of compressibility

= 2000 kips/in.

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right slab.

Aspect ratio=ratio

of square width to square span. The slab referencing system used in Figure I and throughout the Paper is; S; signifies a solid slab, and is replaced by B for a slab with edge beams. Zero, 20, etc; refers to the skew angle oft he slab. 0.7, 1.0 etc; refers to the Aspect Ratio B/L. Using the simple strip method ofana]ysis, i.e. assuming a simple statical distribution ofload, then longitudinally; M dead
=

INTRODUCTION
, Short span highway bridges form a large percentage of the total number of bridge structures constructed in this country. For obvious reasons little or no prestige is associated with their 'analysis, design or construction, particularly in view of the abundance of medium and large span structures. Nevertheless, because of the large expenditure as well as the sheer quantity of numbers of such structures, a closer investigation of the methods of analysis and design is justified. Traditional analysis (based on BS 1531 and Ministry of Transport Memo 771 2 and design for simply supported right slabs subjected to type HA loading is an easy two-step problem; . Step 1. A simple statical distribution of load is assumed, thus enabling the designer to work with a "one foot strip" of the slab, and the mid-span moment is obtained directly, Calculation of the longitudinal reinforcement is then made. Subsequently, checks of the ultimate load condition and crack widths are carried out. At this stage the design calculations are generally complete, as the transverse reinforcing steel is almost always automatically selected at 0.5 sq. in/ft (mild steel) for right slabs. Type HB loading is not usually a great problem to the designer as BS ] 53 part 3A allows type HA loading to be taken as approximately equivalent to 45 units of type HB loading. Difficulties are experienced when the skew angle increases significantly, or if subsidence can cause a transverse rotation of one abutment. In these circumstances a more sophisticated analysis is required. Rusch and Hergenroder (1961)(3) produced a series of "Influence surfaces for moments in skew slabs", these influence surfaces being based on model tests, with nominally rigid supports. These influence surfaces have been widely used for the analysis of skew slabs. The powerful finite element method(4), (5) is capable of solving numerous problems including the two mentioned above, and the authors have used a finite element programme to solve all the slab problems of this Paper. The slabs have been assumed to be supported on flexible (i.e. rubber) bearings. Throughout the elastic analyses the assumption has been made that the reinforced concrete slab can be replaced by a slab of homogeneous, isotropic material. This assumption is clearly not strictly true for either orthogonal or skew systems of reinforcement. However, the analyses will provide a field of bending moments in equilibrium with a given loading and providing the reinforcement is placed accordingly then satisfactory working load behaviour will generally be achieved. Step 2.

468 L2

154,200 lb ft/ft.

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220 L2

+

2700 L

8

4

107,200 live 154,200 dead 261,400 Ib ft/ft

Total design moment

Transversely, if the Ministry of Transport assumption is used, i.e. that 0.5 sq. in of mild steel reinforcement per foot width provides a satisfactory moment of resistance, then no calculation is required. This method assurn.es twisting moments are zero, or rather that they may be reasonably ignored. (2) The finite element analysis, with type HA loading. Using the same parameters and the principle of superposition, Table 1 has been prepared.

TABLE Slab Node

1 units Ib ft/ft

Mx 248,000 241,000

My 8,260 27,100

M.y 1525 11

43 46

Directional design moments M' and M; are easily calculated from these moment fields using the equations given by Wood ( 1968)(6) M~ M~

= Mx +IMxyl
=

(I) (2)

My+IMxyl
249,5OOlbft/ft 27,IOOlbft/ft

and from these equations Mi
= =

M}

Analysisof

Right Deck

(I) The simple strip method, with type HA loading. Figure I shows details of the slab, the following parameters being used in the calculations. span/depth ratio 18 :1, (thickness of slab 2.8ft) self weight 420 Ib/sq. ft surfacing 48Ib/sq. ft uniformly distributed live load 220 Ib/sq. ft - over whole slab knife edge live load 2700 lb/ft over 24ft carriageway.
34 THE JOURNAL OF THE INSTITUTION OF HIGHWAY ENGINEERS

As would be expected, the finite element analysis gIves a slightly lower value for M: than the simple strip method, since the knife edge load is distributed over the whole width of t,he slab. Figure 2 shows how the moments of the knife edge load only, are distributed across the mid-span section. It should be noted that the moment of resistance provided by 0.5 sq. in/ft of mild steel transverse reinforcement is 30,000 Ib ftlft, hence in this case the nominal amount of transverse steel is adequate. It should also be noted here that the uniformly distributed load has been assumed to act over the whole slab. This of course is an
AUGUST 1970

The Analysis and Design of Short Span Skew Highway Bridge Slabs
approximation, but since the increased footpath surfacing thick. ness and the footpath loading should also be included the moments, as calculated, are on the conservative side. The previous example is now continued using this modified type HA loading. The moments at the critical nodes are shown in Tab]e 2. Directional design moments may be calculated as before, M; 263,670 Ib ftlft

D

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M;

25,850Ib ftlft TABLE 2

<=

E <> E

~ Slab Node
knife edge load applied oyer this wid1h onl~
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units Ib ft/ft M" My M"y

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43 46

262,000 252,000

8,400 25,850

1670 4

Figure 2 Longillldinal moment for knife edge load
span.

01

mid-

Modified Type HA Loading
An alternative solution, simpler and slightly more approximate, is to modify the type HA loading by neglecting the knife-edge loading and increasing the uniformly distributed loading to compensate. When considering type HA loading on a strip of slab the two components of live load are both very significant. However, with certain reservations, an equivalent uniformly distributed loading can replace the strict type HA loading without altering the intended effect. If the type HA loading is replaced by a modified uniformly distributed loading which produces the same maximum mid-span moment, then it can be shown that the envelopes of bending moment, based on a one-foot strip, are the same for the modified and the strict type HA loads. The modified type HA loading, W m, to produce the same maximum mid-span bending moment is: (3)

It is seen that for the modified HA loading the moments are approximately 5 per cent higher for longitudinal moment and 5 per cent lower for the transverse moment; the twisting moments are seen to be insignificant. These changes are to be expected since the modified uniformly distributed loading replaces the knife edge load which only acts over the carriageway width. Since Figure 2 shows a very good transverse load distribution of the knife edge load, it would be a simple matter to factor this in the ratio (24/36). If this is done longitudinal agreement is closer to the strict type HA loading. However, without this modification the longitudinal moments are on the conservative side and in this Paper the additional factor has not been introduced. The modified type HA loading appears to be a useful basis for comparison of slabs of various aspect ratios and the remainder of this Paper makes use only of this modified type of HA loading.

Analysis of Skew Decks
The five skew slabs of Figure 3(a) are considered. The slab thicknesses have been based on a skew-span/depth.ratio of 18:1 and rounded off to the nearest one-tenth of a foot. Figures 3(b) and 3(c) give relevant node numbers. The following loadings are applied: self weight assuming concrete at 150 Ib/cu. ft surfacing at 48lb/sq. ft live load modified HA as previously described.

Where w is the HA uniformly distributed load W is the knife edge load L is the span The bending moment at any point x on a strip one-foot (where x is measured from the point of support) is: BM modified HA w = 2

wide

[2W] 1+wL

lx-w

[2W] 1+wL

x 2

2

(4)

and it is easily shown that this envelope of bending moment is identical to the strict type HA loading envelope of bending moment, which may be expressed as: BM strict HA
=

X(L-X)[~+~]

(5)

The maximum value of shear force is also identical for the modified and strict type HA loadings. However, it must be noted that it is only at the points of maximum shear that this equality exists and that elsewhere within the span the shear force due to strict type HA loading gives a worse shear condition. This is generally not a serious restriction on the use of this modified loading system when considering solid slabs, as shear is not usually critical even at the supports. The second limitation on the use of this modification is that of transverse bending at mid-span caused by the knife edge load. It is to be expected that a slightly lower value of transverse bending moment will result from the use of the modified uniformly distributed loading. Despite these two minor limitations, it is felt that this modified HA loading is useful for obtaining quicker solutions, particularly when using the finite element programme ..
AUGUST 1970

Figure 3 (a) Range of simply supporled skew slabs analysed.
S~~"'fl "lilt' • S~~.m1p.1.ll .t.f Sp~n/"~,U 1I .s~~rt span

Squn 1p.TI1ll Lt' $pih/,~pl!l 11

o'

C_, .. I,, ~~.I=~
1

'!'
I'

C_l.
I LI

Ii

16

n:;~
SllI/' d

:2:D:I_

116.1_'
I

I-II'
5,,~~/.tplll l!

I,ll'
f

.14

5D

,'~

sUa/H

l/l~111

~~~!J

1r1-=,====

z~.r=~

~ L---!~.~J

I 5~u14 I

;.di;;--)o"'='

Figure 3 (b) Dimensions and node numbers for skew sfab,f,
THE JOURNAL OF THE INSTITUTION OF HIGHWAY ENGIN~ERS 3S

'1 ,
The Analysis and Design of Short Span Skew Highway Bridge ~/abs
5qOlff sp~n )to]'

Sp~nl4rpth

lB

SqU~ff sp~n 34'3' Span Idtplh 18

angles to the abutments, hence the reduced moment. Advantage cannot be taken of this fact (except to a limited extent) as the ultimate moment ofresistance becomes the limiting condition.

w(
t

I
2 ,1
.B

5/45/1-4

'=C;:L:Z:/

z:'

Z::::~B'Z::::"

::;Z'::Ij

Figure

3 (c) Dimensions

and node

numbers

for skew

slahs. Figure 4 Trajectories of principal momenls loaded, ~1ll1ply supported slabs. (Jensen 1941) for uniformly

Tables 3 and 4 show the critical nodes for maximum directional design moments using the equations given by Armer (1968)(7) when applied to the moment fields as calculated from the finite element analysis. Also shown are the appropriate areas of steel, assuming steel working stress fS( =27,000 Ib/sq. in. for the longitudinal high tensile steel and fst =20,000 Ib{sq. in. for the transverse mild steel (assumed to be mild steel). The specification of a constant skew span/depth ratio results in the slab thicknesses varying for the particular cases considered. Hence, the areas of steel and the directional design moments are not in proportion for the slabs with different reference numbers.

Transversely, the directional design moment Mil is seen to be greatly in excess of the moment of resistance provided by a nominal amount of 0.5 sq. in/ft. Jensen (1941) gives an approximate method for calculating the amount of transverse steel, Ast (transverse) = (0.5 sq. in/ft) x sec 29 It is interesting to note that the values calculated in Table 4 fall within the following range:

•

TAB LE 3 longitudinally, Slab reference assuming a skew system of reinforcement Slab node M~ finite element M~ simple strip AS( sq.in finite element moment units Ib ft/ft Ast sq.in simple strip'

5120/0.7
5120/1.4

5/30/1.0 5/45/0.7 5/4611.4

60 92 64 36 63

186,000 182,000 146,000 76,600 116,000

200,000 200,000 203,000 235,800 235,800
TABLE 4

3.50 3.43 2.70 1.19 1.93

3.76 3.76 3.82 3.94 .3.94

Transversely, assuming a skew system of reinforcement Slab reference Slab node M*
II

moment units Ib ft/ft Moment of resistance 0.5 sq.in/ft Ast sq.in finite element

5/20/0.7 5/20/1.4 5/20/1.0 5/46/0.7 5/45/1.4

46 98 69 46 85

57,800 80,500 90,000 101,000 120,000

27,000 27,000 27,000 30,000 30,000

1.39 1.98 2.25 2.23 2.68

It should be noted that a skew system of reinforcement (Figure 3(a) has been assumed for the bottom steel. Smithers (1969)(8) has shown that theoretically an orthogonal system requires less steel than the skew system but it is felt that the latter system is simpler to detail and place. The skew system of reinforcement is therefore used here. Also tabulated are the longitudinal design moments and areas of steel. based on the simple strip method. and the moment of resistance provided by 0.5 sq. in. of mild steel transverse reinforcement per foot strip of slab. From Table 3 it is seen that at the given skew angles the finite element requirement for longitudinal steel is less than the value obtained from the simple strip method. The reason for this is readily seen by reference to Figure 4 (taken from Jensen (1941)(9) which shows the trajectories of principal moments in skew slabs. The maximum principal moment tends to orient itself at right
36 THE JOURNAL OF THE INSTITUTION OF HIGHWAY ENG:NEERS

ASI(transverse) = k(0.5 sq. in/ft) Xsec 29 where k is in the range I to 2 Because of high twisting moments in the vicinity of the obtuse corners top steel is required and Table 5 gives the values. These values of negative directional design moments and their associated areas of steel have been included to give an idea of the magnitudes involved, and no attempt has been made to show the extent of the requirements for such reinforcement. Each problem is different and requires its own analysis, and it is a simple matter in any particular case to find the limit of the area requiring top steel. Optimisation of slab design may in future make it possible to produce design rules in this respect. In the 5{45/0.7 slab it is seen that even at the central node (46) top steel is required. This effectively means that the top steel is required throughout the whole slab, the cause of this requirement being the very high twisting moments present in slabs of high skew.
AUGUST 1970

The Analysis and Design of Shorf Span Skew Highway Bridge Slabs
TABLE 5 Top Reinforcement Slab reference Slab node M~ M~ moment units Ib ft/ft square mesh A'I sq.in

I

~

l

S/20/0.7 S/20/1.4 S/30/1.0 S/45/0.7 S/45/1.4 S/45/0.7

14 26 18 14 26 46

- 8,150 -10,100 -18.600 -19,900 -26,100

-

-15,700 -16,900 -1 9,100 -20,200 -21,000 - 7.260

0.33 0.35 0:42 0.42 0.53 0.10

TABLE 6 Ultimate Moments of Resistance Slab reference , Applied moment Mull finite element Mull simple strip moment units Ib ft/ft load factor. finite element load factor. simple strip

S/20/0.7 S/20/1 .4 S/30/1.0 S/45/0.7 S/45/1.4

200,000 200,000 203.000 235,800 235,000

485,000 478,000 392,000 210,000 330,000

515,000 515,000 522,000 615,000 615.000

2.42 2.39 1.93 0.90 1.40
'0

2.57 2.57 2.57 2.61 2.61

I

The ultimate condition must also be checked and Table 6 shows the applied moment on a one foot strip and the ultimate moments of resistance of these strips based on the amounts of steel as calculated in Table 3. The load factors are expressed as the ratios of these two values. If an overall load factor of 2 is required then it can be seen from Table 6 that at skew angles above 20 degrees the governing criterion for the design of longitudinal moment of resistance is the ultimate condition. If the load factors are considered unnecessarily high at approximately 2.5 a reduced value may be used without over-stressing the longitudinal steel under working loads. This is not necessarily the case for slabs of zero skew to 20 degrees of skew, although in the latter case economy can be gained by a slight reduction of load factor, but the working stresses may then become critical and a careful check is necessary. The overall load factor of 2 chosen is used purely for comparison purposes and other factors may be more suitable in particular cases. Summarising, the longitudinal moment of resistance can be determined from the ultimate state using an appropriate load factor for angles of skew of 30 degrees and over. For skew angles of zero to 20 degrees both longitudinal working stresses and ultimate moment of resistance should be checked. An elastic analysis is required for accurate determination of the transverse design moments. Areas of steel required transversely are likely to be in excess of 0.5 sq. in/ft and even be greater than the empirical value of (0.5 sec2e) sq. in/ft.

....

.
..
", C ..

;; ~
en
C

~so
50 Assuming KA loading span J depl/1 ra1ro 18 surfacing ~8 Ib Jft2

E E ..

E ==
.::! ..

.;:; ", 40

~ ;;:",

..

~ :;;t => .....
"Ci.=
->-

30

.. - 20 "' .. 20

30

~O
Span. feet

50

60

Figure 5 Sell weigh 01 rowl //lomeI/(.

I

and stlrlacing

1tl00llCI1I

liS

a pcrcenrage -

Precast Beam and Infill Concrete Construction
This method of construction is such that the total self weight of the deck is taken by the precast beams which span in a perdetermined direction. It may be assumed therefore that the self weight of the deck does not induce any transverse or twisting moments. (Careful thought must be given to the method of placing the in-siru concrete). It is further assumed that such induced moments are only caused by the surfacing and live loads. It could reasonably be expected that this state of affairs would lead to an increase in longitudinal moments as calculated from an elastic analysis and likewise a reduction in the transverse moments when compared with an ill-siru reinforced concrete slab. The extent of the change in moments due to this different form of construction (assuming that the total construction depth is unaltered), is dependent partly upon the span of the slab. Figure 5 shows, for spans from 20 feet to 60 feet, the percentage applied moment of self plus surfacing for a right slab expressed as a percentage of the total moment. At 20 feet span the self plus surfacing is 30 per cent of the total moment and at 50 feet span the percentage has risen to nearly 60 per cent. This means that in the upper range of this type of construction there is likely to
AUGUST 1970

be a greater saving in transverse steel by using precast beams ... The aspect ratio of the slab and the skew angle also affect the moments. Table 7 shows the longitudinal design moments due to the various load components. Since M~ (total) in Table 7 is less than M~ (total) from the simple strip analysis (Tables 3 and 4) the design may still be based on the ultimate state as this remains the governing factor. From the point of view of moment of resistance in the two design directions it is seen that there is a considerable saving in transverse steel, and that in the longitudinal direction, since the ultimate state is still critical, there is no alteration in the amount required in that direction. It must be emphasised that this example is in the upper part of the range, therefore the savings in transverse steel are large and it is likely that this would be an influencing factor in the choice of construction, whereas at the other end of the range it is possible that though savings in transverse steel would undoubtedly result from the precast beam design, the solid slab may still be a more overall economic choice.

,'

45degree SkewSlab Subjected to Type HB Loading
As an interesting comparison with type HA loading the HB trailer was placed in seven different positions on slab S/45/0.7, which positions could possibly give rise to maximum longitudinal and transverse moments. The worst HB position was determined and comparison is made with the moments obtained when strict type HA and modified type HA loading are applied to the same slab. Tables 8, 9 and 10 show the critical nodes and the appropriate directional design moments.
THE JOURNAL OF THE INSTITUTION OF HIGHWAY ENGINEERS 37

The Analysis and Design of Short Span Skew Highway Bridge Slabs
TABLE 7 Precast beams with infill concrete M: due to surfacing + live 94,000 74,500 36,400 TABLE 8 Strict type HA loading Loading udl220 Ib/ft2+surf. 48ft2+self weight knife edge load over carriageway Total TABLE 9 Modified type HA loading Loading. udl331 Ib/ft2 +surf. 48Ib/ft2+self weight TABLE 10 H B load 45 units Loading HB load + self weig ht + surfacing Total
It is seen that the modified type HA loading is in closer agreement with type HB loading than strict type HA loading. The authors, however, are not certain that the literal interpretation of BS 153 part 3A should be applied to skew slabs. In these calculations it has been assumed that the HA knife edge load acts at mid-span parallel to the abutments. Since the slab is at 45 degrees of skew the total value of the knife edge load is; y2 x 16 x 2700/2200=27.3 tons. lfthe slab has been of zero skew the total load would have been only 19.35 tons. This means that this structure is subjected to a knife edge load of more than 40 per cent greater than a right structure, a considerable increase. The effect of the knife edge load on the transverse directional design moment is seen to be very considerable, and indeed the total M Ii moment for the strict type HA load is seen to be approximately twice the value obtained from the 45 units of HB loading.

moment units Ib ftlft M~ total 192,500 174,500 160,400 M~ due to ~urfacing+live 29,300 45,700 48,000 All sq.in transverse 0.66 1.15 1.04

--

Slab reference S/20/0.7 S/30/1 .0'

M~ due to slab 98,500 100,000 124,000

5/45/0.7

~

units Ib ft/ft Slab node 46 46 92

j

M~
66,000 8,300 74,300

Ma

•

87,200 ,138,000 225,200

units Ib ft/ft Slab node 46

M;
76,600

Ma

•

101,000

units Ib ft/ft Slab node 46 46 92

M~
48,500 20,000 68,500

Ma

•

52,000 62,000 114,000

gained from the more effective disposition of the materials, the edge beams attracting moment and being capable of carrying large moments due to the increased lever arm. Simply Supported Right Slabs subjected to Rotational Subsidence In medium span highway bridges (80-120 feet span), much consideration is given to the torsional rigidity of the deck if the bridge is located in a mining subsidence area(IO). Viaducting is either constructed in concrete as a series of simply supported pre-stressed beams with a top slab of concrete to give this low torsional rigidity, or continuously in steel which has inherent qualities which can accept the likely deformations. For short span bridges it appears that simply supported slabs in solid reinforced concrete are frequently designed on reduced working steel stresses, and it is assumed that the slab will then be capable of withstanding the induced twist.

j

1

Slab with Edge Beam Construction Another possible form of construction is to use a reduced thickness of slab together with edge beams. This type of construction is not much used, perhaps because of the only recent availability of suitable methods of analysis. The authors have carried out analyses on a limited number of such decks and it appears that at low aspect ratios this form of construction is likely to be more economic than either the solid in-situ reinforced concrete, or the precast beams and infillconcrete. As the skew angle increases the saving of longitudinal steel becomes greater, and this type of construction becomes more efficient. The underlying principle to these comments is the basic fact that the greater the skew angle of a slab the greater the twisting moment due to the applied loading. The slab and edge beams type of construction is freed of this increasing twisting moment because of its low torsional rigidity. In a deck of zero skew though the twisting moments are small, an advantage is
38 THE JOURNAL OF THE INSTITUTION OF HIGHWAY ENGINEERS

Figure

6 Transverse

rotational

sefffemem

of

one abutment.
AUGUST 1970

The Analysis and Design of Short Span Skew Highway Bridge Slabs
Three slabs subjected to a transverse rOlation of one abutment of the type shown ip..Figure 6 are investigated. A rotation of 1 in 360 is used, the bearings are assumed to be rigid and details of the slabs are shown in Figures 7(a), (b) and (c). Table 11 gives details of the directional design moments induced and the areas of steel required to cater for these moments.

F=========t
--rHode 46 No lieUiement of /" [hili ibulmenl
, Hade 43

Slib

B IZera

10-1

V~rlicil HtUemenl 0.100'

o' 083'
0'067' O'OSO' O'OJ3'
O' 011' 1'5'

Yortiul
s.lllemul

Slib sjZuo/01

0.100'
HU' O' 06/'

Zero IsflUement _____ 5_l-_4._.~

-l

I-L-

I

+Nade h stili ~menl of /'Ihis ibulmenl

~6

H50' 0'033'
O' 011'

Figure 7 (c) Slab with edge beams. rotational subsidence.

Nod~ '3 /

/

Zero Istlll.m~nli

5.' " ..,.........., Abutm.nt rolilian l'360

k
~8

Figure 7 (a) Slab supported over full width. rotational subsidence.
Vor1ical seltl~me~1 0,,,1' 8-050'
36 24' tN.d. 46 0'033' 0,01&1' t1-N.d. 43,

Slib S IZera 10./ r-

hra stIli em.. '

l

SI'"

I

J~.

Figure 7 (b) Slab supported over reduced widlll, rotational subsidence.

The areas of steel shown in Table 11 have been calculated assuming a steel stress of 27,000 lb/sq. in. for the longitudinal steel and 20,000 IbJsq. in. for the transverse steel. However, for the case of edge beams and slab the steel in both directions has been assumed to be high tensile steel at a working stresses of 27,000 lbjsq. in. Tt is seen to be slightly advantageous to support a slab over a reduced width, but the saving in longitudinal and transverse steel is small. However, the slab with edge beams is seen to be more efficient, indeed the increases in slab steel are only in the order of 1.4 per cent and 6 per cent for the longitudinal and transverse steel respectively. The edge beams are seen to have similarly small increases in moment. Steel in the edge beams has not been designed in these examples, but it should be noted that suitable torsion steel must be provided. In general even for bridges not subjected to transverse rotational settlement of one abutment this type of construction requires less steel and concrete, and since the weight of wet concrete is considerably reduced the supporting formwork may be less costly. Against this is the extra expense of the more complex steelwork.

TABLE 11 Rotational Subsidence of Abutment M~ 264,000 My As! sq.in 4.47 0.50 4.83 1.50 5.50 1.66 4.38 0.50 4.60 1.34 5.40 1.40 2.80/1.78 1.71/1.15 2.84/1.90 moment Loading units Ib ft/ft Slab node 43 46 Slab supported overfull width 43 46 43 46 43 46 Slab supported over central 24 feet 43 46 43 46 43 46 Slab with edge beams. Supported overfull width 43 46 43 46
AUGUST 1~70

Slab reference

condition

283,300

26,000

self+live no subsidence self +surfacing +subsidence total load + subsidence self+live no subsidence self+surfaci.ng +subsidence total load + subsidence self+live no subsidence self+surfacing +subsidence total load + subsidence
3~

70,580
-

385,800

260,000

81,000

19,000

273,220

60,700

384,200

68,750

63,000 102,500 50,500 65,030 76,400 107,030

67,300 41,333

-

69,000

THE JOURNAL OF THE INSTITUTION OF HIGHWAY ENGINEERS

I

-

---------------------------------------------------------IIIIIIl,-,
The Analys;s and Des;gn oj Short Span Skew H;ghll'ay Brhlge Slabs
Conclusions
The finite clement method is particularly useful for the analysis of a continuum such as a solid in-sifl/ reinforced concrete highway bridge deck, always provided that it is acceptable to idealise the deck into an elastic isotropic or orthotropic slab. All the slabs ana lysed in this Paper are assumed to be isotropic. Type HA loading as specified in BS 153 part 3A, (i.e. a uniformly distributed loading plus a knife edge loading) may be replaced by an increased uniformly distributed loading without significantly affecting the directional design moments. It appears that for right slabs with an aspect ratio of less than unity the traditional method of analysis and design, based on a one-foot-strip, and assuming simple statical distribution of load is a satisfactory design approach. Forslabs with a skew angle in excess of20 degrees the governing criterion for the longitudinal steel, in the slabs analysed, is the ultimate moment of resistance. For the transverse steel an elastic analysis is required if the working stresses are to be limited. Areas of transverse steel, as calculated by the finite element method assuming isotropic slabs, are likely to be considerably in excess of 0.5 sq. in/ft for slabs with large angles of skew. Similarly an elastic analysis is required to determine the quantity of top steel and the extent of the area over which this top steel is required. At a skew angle of 45 degrees and aspect ratio of 0.7, top steel is required over the whole slab because of high twisting moments. At high skew angles a saving in quantity of transverse steel is possible by using precast beams and infill concrete; this method of construction does not affect the moment of resistance required in the longitudinal direction. Clause A6 of BS 153 (which permits HAloading to be taken as approximately equivalent to 45 units of HB loading for slabs) appears to te unreasonably conservative for slabs of high skew when considering the transverse design moment; whereas good agreement is obtained between the suggested modified HA loading and the abnormal loading of the HB trailer. In mining subsidence areas ifan assessment can be made of the likely rotations then a suitable .elastic analysis can enable the working st~1 stresses to be kept within the permissible limits. A particularly useful type of construction in such circumstances is the slab and edge beam construction.

Acknowledg ments
The major part of this work was undertaken as part of an M.Sc. dissertation written by under the general direction of Professor A. are due to Professor O. C. Zienkiewicz for element programme and to the computing University. at Leeds University one of the authors M. Neville. Thanks the use of his finite centre at Swansea

References
(I). British Standard 153 part 3A, Specification for Steel Girder Bridges. British Standards Institution, 1966. (2). Ministry of Transport Memorandum No. 771, H.M.S.O. ]961. (3). Rusch, H. and Hergenroder, A., Influence sl/rfaces for //Ia//lc/Us in skew slabs. Cement and Concrete Association, 1961. (4). Zienkicwicz, O. c., and Cheung, Y. K., The jinife demem mefhad j()r the analysis of elastic isofropic and orrllOfropic slabs. Proc. I.C.E., vol. 28, August 1964. (5). Zienkiewicz, O. c., The jlllife elemenf method ill sffllcftlra/ and caminlll/m mechanics. McGraw Hill, 1967. (6). Wood, R. H., The reinforcemelll of slabs in accordance with a predefermined field of 1I10ments. Concrete, February, ]968. (7). Armer, G. S. T., Discussion of Paper by Wood.(6) Concrete, April 1968. (8). Smithers, N. J., The analysis and design of skew highlmy bridge slabs. M .Sc. dissertation, University of Leeds, ]969. (9). Jensen, V. P., Analysis of skew slabs. University of Illinois, Bulletin No. 332, Septemcer 1941. (1O).Sims, F. A., and Bridle, R. J., Bridge design in areas of mining subsidence. The Journal of the Institution of Highway Engineers, November 1966.

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THE JOURNAL OF THE INSTITUTION OF HIGHWAY ENGINEERS

AUGUST 1970

l
East Midland Branch

The Effect of Work Study and Financial Incentives in Highway Maintenance
R. S. Tricker, M.I.W.S.P., M.R.S.H.

BIOGRAPHY
The author is currently Honorary Secretary to the Bedfordshire Branch of the Institute of Work Study Practitioners, a Council Member of the Local Government Work Study Group and Chairman of the Local Government (County Highways) Advisory Group. He formed and developed a Work Study Section in the County Surveyor's Department, Bedfordshire County Council and is now head of the section as part of the Management Services. He is also undertaking investigations into other service departments within the Authority.

SUMMARY
This Paper defines work study and discusses the effect of its application, in particular its impact at management level on maintenance work in highway departments. It discusses productivity bargaining, the principles of incentive schemes and the payment of financial incentives based on work study. The purpose and the need for and significance of the presence of trade unions in this area of work is underlined in the section dealing with management/ employeerelationship. The importance of communication as a control is discussed in some detail, together with the need for training in work study at alllevels. In general. this Paper sets out to show how the applications of work study techniques can aid management in their endeavour to improve productivity. This Paper was presented to the East Midland Branch meeting at Bedford on December 9th, 1969.
AUGUST 1970'

1. INTRODUCTION After the introduction of Work Study to a department, engineers will find themselves talking about highway maintenance and its problems in a manner previously unknown to them. At the present time officially inspired financial strictures are dictating the use of new measures in an endeavour to improve the productivity of resources employed. Work Study is one of these measures. The resources are labour, materials, capital equipment and space. To employ Work Study a more detailed knowledge of maintenance work is needed and it must be quantified to finer limits than has previously been the custom. It will be necessary to describe the various parts of the work and to specify methods of working; to indicate appropriate management control and to state the tools and equipment and other resources to he employed in the execution of the work. Work will be' planned and programmed in greater detail than before and, in due time, will reward labour according to its performance by paying in addition to basic rate of pay. Terms normally unfamiliar will find common usage, terms like management control(s); financial control(s); communications; feedback; standard minutes. Costing methods and procedures will fall short of requirements, and it will be necessary to spend time in developing more relevant systems. Whilst traditionally good relationship with men has been enjoyed, based upon mutual respect and understanding, there now approaches the additional dimension of productivity bargaining and all that follows from this. It will be necessary to illustrate productivity, to the Authority and to the National Joint Council on behalf of the'
THE JOURNAL OF THE INSTLTUTION OF HIGHWAY ENGINEERS 041

I
The Effect of Work Study and Financial Incentives on Highway Maintenance
National Board for Prices and Incomes, and to state it in respect, of each scheme involving the payment of financial incentives. The merits or otherwise of the various schemes will be argued and the engineer will be concerned -as never before with "measured" and "unmeasured" work of a productive nature; "lost time" ; "operator / overall performance" ; "cost per standard hour" etc., and discover the importance of the Code of Guiding Principles. This Code was issued to Local Authorities by the National Joint Council for Local Authorities' Services (Manual Workers) in December 1965, and has become the mandate for the introduction of Work Study by local authorities. It is inevitable that the engineer will find himself dealing with the resentments and frustrations that accompany change, and he will discover that these are at all levels of staff, and men, and that no small measure of patience and determination is required in order to be able to deal with them successfully. The author is sure that an enthusiastic understanding of newly acquired Work Study techniques and the interest they offer as their use is developed can be achieved. 2. WORK STUDY AND MANAGEMENT
(i) Work Study

Work Study is an aid to management and is "the systematic objective and critical examination of all the factors govern-, ing the operational efficiency of any specified activity in order to effect improvement." This potent definition is that of the late Mr R. M. Currie. The value of objective analysis and measurement and of the constructivefy critical attitude embodied in Work Study has been proved again and again. The fields of application of the service are:(a) Labour control (b) Production Planning and Control (c) Materials handling (d) Plant and Product design (e) Incentive Schemes Work study in any organisation should be preceded by appreciation courses for all levels of staff and men, such as will afford them a proper understanding of its purpose, the need for it, and how it can be used. It is not a substitute for good management, but is a most powerful tool at the disposal of management to assist the day-to-day business of developing and directing the organisation for work. It is nothing by itself. Its value is dependent upon the extent of its use by engineers and foremen in their capacity as managers. Men trained and qualified in particular disciplines are prone to resent what at first appears to them to be an intrusion into their professional spheres. No Work Study officer doubts the need for professional skills, or sees work study practice as a substitute for them, but it may be found that in this area of work particularly the engineer is "long" on engineering skills and "short" on management skills. (ii) ManagementOperational efficiency is the responsibility of management; that is of all those who contribute to the "organisation and control of human activity directed to specific ends". The definition is again that of Mr R. M. Currie. "Organisation" encompasses a planning function and "control" the implementation of the p~an.

Work Study is, of the need for it and how it can be used. Major financial benefits will be derived from the application of Method Study and Work Measurement to highway maintenance and procedures for work developed such as will enable the maximum return from the incentive bonus payments that follow. Method Study and Work Measurement should precede financial incentives. This order of preference is difficult to realise for the immediate future. Local authorities have failed to maintain an adequate pay structure for manual workers. The effect of this and the attempts to deal with it coincide with a time of economic pressure which produces nationally a demand for improvement in productivity to match increased labour costs. Hence the accent is on the need for improved management, an acknowledgment of management techniques, and the energy and initiative to implement them in a way formerly unknown in local government generally. The immediate impact of this, since at this late stage it is not possible to secure the provision of properly trained Work Study staff in a short enough time, is that many authorities will be embracing Work Study in reverse via financial incentives. This is an added reason why it is important that those who manage should have a good knowledge of the various systems of payment by results and their shortcomings and limitations, as well as of the advantages to be gained from their use. Because financial incentives will inevitably be an important early result of the application of Work Study to maintenance work, a closer look should be taken at the purpose of their application and the way in which they are applied. Financial Incentives raise the take:home pay of the man and may have the effect of assisting recruitment. The essential purpose and reason for financial incentives is that they improve the performance, and therefore the productivity of labour.
(i) Principles of Incentive Schemes

Work study incentive schemes are designed so that an employee is paid a reward, additional to the job hourly rate, systematically related to his own effective contribution to the achievement of objectives specified by management. The amount of work he personally does is measured in terms of units of work performed. The schemes are therefore based on work measurement data which must be obtained by proper application of the appropriate techniques
(ii)

Financial Incentives based on Work Study Because standard times enable jobs of differing type and duration to be expressed in terms of the same denomination, they provide a basis for the operation of a system of payment by results. The availability of the work specification for use as the contract between managers and worker in this connection establishes precisely the conditions under which a job is to be performed as well as the method employed. From the worker's point of view, the ability to calculate bonus earnings easily is important. Although there is no substitute for good planning, and supervision, incentive schemes of this type have the added advantage that there is every encouragement for workers to pay attention to delays and record waiting time, thus making it apparent to management when and where action may be necessary to prevent their recurrence. (iii) Natural Teams When a number of men work as a team, performance calculated on a team basis. is

3. FINANCIALINCENTIVES
Financial ,Incentives are the result of a system of wage or salary payment which is related to factors in a worker's performance other than that of the time spent at work. Although such payments involve work measurement, the use of Work Study, of which work measurement is a significant part, does not automatically or necessarily imply the need for such payments; that it often does (or that the decision to implement Work Study often follows financial incentives; or even that Work Study is construed as meaning financial incentives) is' the result of a lack of understanding of what
42 THE JOURNAL OF THE INSTITUTION OF HIGHWAY ENGINEERS

(iv) Additional Objectives Earlier types of incentive schemes had improvement of the rate of output per man hour as their main objective. In many cases, objectives such as improvement in the use of materials and services and plant may be much more significant financially. (v) Effect of Incentive Schemes ... They provide management WIth an lllcrease m the output of effective work of the employee, a sound basis of labour
AUGUST 1970

The Effect of Work Study and Financial Incentives in Highway Maintenance
-..--control, in that changes in- the levels of performance are measured and made available, and are consistent means of rewarding- an employee in relation to his own effective con. tribution to work. They provide for the employee the opportunity to earn for , himself a higher standard of living. They can effect dramatic improvement on labour turnover, absenteeism and management-labour relations. 4. MANAGEMENT-EMPLOYEE RELATIONS Notwithstanding the good relations between management and men in highway departments in local government, there is a need for further thinking about this relationship. Work Study investigations will inevitably lead to management decisions that give rise to major alteration to present ways of working, and the traditional concept of a madman's work will be changed. These circumstances make imperative the closest understanding between management and the men and their representatives, the trade unions. The trade unions by now know what is required of the men and of -local authorities, and they have a competent approach to the problems involved. This is a fortunate circumstance and one of which the utmost use should be made. The engineer is now concerned with productivity bargaining in which both sides , will be talking about utilising the total resources of the department in order to produce greater returns for the future. There is a common objective. The trade unions recognise this (indeed this sentiment was recently expressed by a Trade Union National Secretary) and whilst seeing the opportunity to gain reward for their members, they have accepted the mandate given them and local authorities, through the National Board for Prices and Incomes' Report No. 29. Their enthusiasm should be matched by management determination. It is certain that there is room for much greater employee participation at the planning stage, and evidence that this will result in a happier atmosphere for work and earlier achievement of aims and objectives. It may be that in addition to being fully informed of the Work Study and incentive bonus payment procedures, men should be directly involved at the problemsolving stage of the studies. 5. COM MUNICATIONS To communicate is to express thought and feelings to other people. To express thought and feelings is to transmit information and this gives rise to understanding. The whole success of Work Study is dependent upon management at all levels knowing what it is, its purpose, the need for it and how to use it. It would be understandable if this was felt to be a statement of most elementary fact, yet it is more often noticeable for its omission than for its inclusion as part of the introduction prOCess,and the consequences are grievous. The engineer will find perhaps with no little surprise that communication in connection with his everyday work is not what he thought it would be and certainly-not what it should be. And he may well experience annoyance at the realisation of the dramatic ill-effect that the lack of the most elementary commonsense in this matter will occasion. To "play your cards close to your chest" is to deny any possibility of efficient operation in the organisation and control of highway maintenance. (i) Communicaoon as a Control Men must have all available information. Not only must they have a specification for work together with the supervisory control for it, but such other information as will enable them to understand their own part in the work, and, where incentive bonus payments are made, the way in which they will be rewarded for their effort. . Men whose work is to be changed must know this well in advance and they must know why, how it will effect them and the advantages of it. They must be invited to comment and know that account will be taken of their views. A foremen's communication is two-way. To and from the site and to and from their next higher point in the management line. Site supervision is of the utmost importance and this is the point at which all knowledge of the job should reside. Plans, specifications, schedules, costs should all be in the possession of the foreman. He cannot otherwise supervise, and neither will he be able to maintain and develop the interest necessary for sustained effective control. If there are any gangers or foremen on works who are not in possession of all the data relevant to the work they are doing; or who are .not continually informed of relevant decisions that have followed the commencement of works, a breakdown in communication results which will impede the attainment of desired performance levels and the lowering of unit costs. Similar comment applies at each management level. (ii) Training Training is a communication of knowledge and ideas and is essential to the process towards maximum improvement in productivity. A man untrained in the skills and uses of equipment to be deployed is unlikely to order work so as to achieve significant improvement. -A manager who does not understand this, who has not informed himself and does not see that all men and staff understand what is required of them and that they have an knowledge of their job, cannot realise their potential. 6 CONCLUSION Since this paper deals only with the subject of Work Study and Highway Maintenance in broad general terms, the author hopes that it might have been useful to accent "areas" in which Work Study assignments often reveal management weakness. Communication and control are basic to operational efficiency. Management can and should leave the application of techniques to Work Study practitioners, but how to communicate and control and an understanding of the need to do so, is of paramount importance when the engineer comes to apply the findings of the investigations which he has commissioned.

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AUGUST

1970

THE JOURNAL

OF THE INSTITUTION

OF HIGHWAY

ENGINEERS

43

-

New plant, equipment and materials
Small Bus A new small bus, ideal for education, welfare and personnel transport has been launched by J. H. Sparshatt & Sons Ltd., of Burmeld Road, Portsmouth. Designed to accommodate 20 to 22 seats it combines big bus comfort and space with the manouevrability and ease of handling that comes from using a lighter chassis. Based on the British Leyland 420 FG 129in. wheelbase chassis, its sturdy ,steel frame construction ensures a very rigid body and long life whatever the conditions of operation. For this reason it is suitable for many overseas markets, particularly the Middle East and Africa. Principal dimensions of the bus are: o~erall length 19ft. 6in., overall width 7ft. Iin., overall height 8ft. lOin., inside length 12ft. 4ins. inside width 6ft. 11ins. and interior height 6ft. ' A choice of engines is offered - six cylinder four litre, petrol engine or four cylinder 3.8 litre diesel engine. Unladen weight is three tons. The body is framed throughout in heavy duty mild steel rectangular and folded sections. again designed with the export market in mind. Exterior panels are of aluminium alloy. front and rear body sections are one piece g.r.p. mouldings These are so designed that they accommodate interchangeable front windscreens and rear windows. rnterior panels are of mild steel faced with coloured plastic. The roof and front and rear of the bus interior is lined with one piece moulded glass fibre colour-pigmented. The floor is constructed of heavy resin-bonded ply with linoleum cemented under aluminium wearing slats. Windows include top sliding ventilation sections. Front windscreen and rear window are interchangeable curved safety glass units. The choice of seating ranges from timber'slat seats for works buses to fully upholstered seats with head rolls for semiluxury bUses. A luggage boot, luggage racks and other extras can be fitted if required. Infra-Red Imaging System AGA(UL) Ltd., Kew Bridge Road. Brentford. Middlesex. showed their new Thermovision Model 680 infra-red imaging system for the first time in the U.K. at the T.E.A. Exhibition held at Olympia in May. Measurements can be made at any distance from the object viewed in a normal atmosphere without anv reduction in sensitivity and the dual isotherm function facilitates rapid and accurate temperature measurement. Compact and light-weight. with a fast prism scanning svstem and real time picture presentation. the Model oRO covers a temperature range of - 30°C to 2000°C and can focus from 0.5 m to infinity with a sensitivity of 0.2"C. The closely related AGA ThermoprofiIe incorporates a built-in electronically controlled temperature reference source and is designed for instantaneous presentation of absolute temDerature levels from - 20°C to 1Ooo°C. Output signals are available for process control offering a unique facility in incinstries as diverse as olate glass. steel and rubber. AGA al<;o demonstrated their Geodimeter svstem. which mpasures distances from 15 metres to 60 kilometres to an accuracv of a few millimetres. using either tungsten ilIumina"tion or a safe low-power laser for the longer distances.
..... THE JOURNAL Of THE INSTITUTION Of HIGHWAY ENGINEERS

Front Wheel Drive loader
Massey-Ferguson (United Kingdom) Ltd., Banner Lane, Coventry, have announced a new front wheel driver loader, the MF I L Field trials of this Perkins-powered machine have indicated impressive savings potential in terms of cost per ton moved. Other features are outstanding reliability, easy maintenance, good visibility and a high degree of operator comfort. The MF II has a rated payload of 184 kg (4,000 Ibs) and a tipping load of 3629 (8,000 lb.) Standard bucket is I cU.m. (It cu.yd.) capacity but for light materials a 1.5 cU.m. (2 cu.yd.) bucket is available. An important factor of this type of machine is the small turning circle which for the MF II is only 804m. (27ft. 6ins.). Operator comfort and good visibility have taken high priority in the design. Non-slip steps allow safe access into the weatherproof cab which has doors and sliding windows on both sides. Full instrumentation, heater. deminster with variable flow control, front'and rear screen wipers, an adjustable padded seat, a clear uncluttered platform and just three turns to give lock to lock turning are all provided. Driving technique is simple also. With foot-operated hydraulic directional shift. the loader controls under his right hand, and the steering wheel with full power steering under the left hand, the operator can achieve fast cycle times with. out fatigue. In carry position the bucket is positioned close to the machine for maximum stability but an added advantage is achieved as full bucket loads are carried close to the drive axle thus giving the best possible traction. Industrial Thermostat An entirely new range of non-indicting industrial thermostats is announced from Actuated Controls Limited of Bristol. These thermostats designated Models 'TC' and 'TCI A' are produced in nine standard temperature ranges covering from -80.C to +350°C., the model 'TC' thermostat is of the closedifferential type and the 'TCI At unit is of the high {low temperature differential type and is effectively two thermostats in one instrument it incorporates two micro-switches an~. can be pre-set to operate at any two pre-determined points over practically the entire temperature range. The temperature responsive system of this new thermostat is of the vapour pressure type and consists of a precision capsule connected to the sensing probe with a length of capillary tubing. Various tvpes of probe mounting glands and thermo-wells can be supplied to suit the application. When a thermo-well pocket is fitted. the thermostat sensing probe can be withdrawn from thp. vessel without draining the contents. An important design feature is the provision of a pressure setting dial calibrated to within 2 per cent of full scale. This offers a greater scale length than the conventional straight line scale rn addition, the setting friction of the dial can be adjusted to a convenient torque where frequent alteration of pressure' setting is required. or alternatively locked tight to deter alteration. Though the mechanism has very few moving parts subject to wear, judicious use of stainless steel for certain closetolerance components has enabled an average repetition accuracy of plus or minus 0.5% to be achieved. The thermostats can be operated in an ambient temperature of up to 60°C and a variation in operational accuracy over the ambient temperature range from minus 20.C to 6O.C or less than 1 per cent.
AUGUST 1970

Institution matters
ELECTION OF M EM BERS
Total Membership 5th JUNE, 1970 MEMBERS Fairfull, A. C. (Senior Engineering Assistant, Argyll C.C.). Frain, T. (Chairman & Managing Director), Wrekin Construction Co. Ltd.). Giffin, T. G. (Principal Assistant Engineer, Londonderry C.C.). Harris, R. S. (Associate Partner, Howard Humphreys & Sons). Hay, W. D. (County Surveyor, Aberdeen-shire C.C.). Marshall G. L. (Associate, De Leuw, Cather (Australia) Pty. Ltd.). Wadsworth, J. T. (Principal Assistant Engineer, Manchester C.B.C.). TRANSFERS FROM ASSOCIA TE MEMBER TO MEMBER Cucksey, I. T. (Deputy Chief Engineer, Redditch D.C.). Douglass, M. (Regional Traffic 'Engineer, Christchurch Regional Planning Authority, NewZealand). Evans, D. G. (Principal Assistant Engineer, Glamorgan C.C.). Whelan, M. N. (Group Engineer, Midland R.C.U. (Warks. C.C. SubUnit». ASSOCIA TEMEMBERS Ackroyd, D. S. (Senior Engineering Assistant, Staffordshire C.C.). Alston, J. A. (Miss) (Project Engineer, Skelmersdale D.C.). Barron, P. J. (Assistant Engineer, Colchester B.C.). Bastable, J. E. (Civil Engineer, Ministry ofTransport). Brown, A. (Assistant Engineer, Harry' Brompton & Partners). Christie, P. B. (Assistant Engineer, Stirlingshire C.C.). Clarke, M. C. (Graduate Assistant Section Engineer, Cumberland C.C.). Cunningham, R. R. (Assistant Engineer, Babtie Shaw & Morton). Currie, J. V. (Senior Assistant Engineer, Lancashire C.C.). Dick, R. R. M. (Assistant Engineer, Stirlingshire C.C.). Dishington, J. V. (Conservancy Engineer, Forestry Commission). Edmondson, B. (Assistant Engineer, Herts. C.C.). Farmer, M.' H. (Assistant Engineer, Montgomeryshire C.C.). Fazakerley, J. (Engineering Assistant, Lancashire C.C.). to date 7,590. Fowler, A. J. S. (Senior Engineer, Staffordshire C.C.). Gardner, R. D. D. (Assistant Engineer, Ayr B.C.). Gibson, C. (Assistant Resident Engineer, Scott, Wilson Kirkpatrick & Partners). Griffiths, M. B. (Engineer, Wallace Evans & Partners). Haigh, G. R. (Assistant Engineer, Salisbury City C.). Harrison, W. J. (Professional Officer, Traffic & Development Branch, G.L.C.). Herdman, B. (Senior Engineer, Durham C.C.). Hewitt, J. H. (Assistant Engineer, Swansea City C.). Holland, G. (Assistant Civil Engineer, Glasgow City C.). Hutchinson, D. A. (Assistant Resident Engineer, Leeds City C.). Johnson, B. S. (Divisional Surveyor, Cornwall C.C.). Johnston, D. R. (Senior Project Engineer, Babtie Shaw & Morton). Jones, C. M. (Section Engineer, Sir Owen Williams & Partners). Lewis, L. J. (Chief Engineer (Bridgeworks), Sir A. McAlpine & Son}. Lightband, M. S. (Partner, Bylander Waddell & Partners). McGregor, J. G. (Director, Watson & McGregor). Mortlock, R. A. (Assistant Engineer, West Suffolk C.C.). Msaike, A. H. (Assistant Engineer, Harlow D.C.). Pease, A. W. (Assistant Engineer, Coventry C.B.C.). Phillips, T. A. (Site Agent, Droitwich Construction Co. Ltd.). Randall, D. T. (Principal Assistant Engineer (Highways), Leamington Spa B.C.). Roberts, P. L. (Engineer, Midland R.C.U. (Warks. C.C. Sub-Unit». Shaw, C. A. (Senior Engineer, C. H. Dobbie & Partners). Small, E. J. (Civil Engineer, Ove Arup & Partners). Wanjohi, I. G. (Postgraduate Student in Transport Engineering, Imperial College) . Webb, J. D. (Bridge Engineer, SouthEast R.C.U. (Hants. Sub-Unit». Webb, J. F. (Senior Engineer, Freeman, Fox & Partners). Widdop, P. A. (Assistant Engineer, Lancashire C.C.). Wiseman, J. I. (Engineer, Glenrothes D.C.). Wixted, T. P. (Materials Engineer, E.G. Pettit & Partners, Lusaka). Woodhouse, K. J. (Assistant Engineer, Antrim C.C.). Wright, J. A. (Engineering Assistant, Salisbury City C.).
THE JOURNAL

TRANSFERS FROM STUDENT TO ASSOCIA TEMEMBER . Buckland J. J. (Assistant Engineer, Manchester City C.). lyon R. R. (Assistant Engineer, Runcorn D.C.). STUDENT Gillatt A. J. (Assistant Engineer, Irvine D.C.).

PERSONAL

NOTES

Acton, G. D., has been appointed Assistant Engineer with Dudley County Borough Council. Bakhda, J. M., formerly Town Surveyor, Cookstown, Northern Ireland has been appointed Deputy City Engineer, Kitwe City Council, Zambia. Baldwick, K. M., has taken up the post of Divisional Surveyor, Wokingham Division, Berkshire County Council. Barrington-Hines, H. J. K., is now with the County Surveyor's Department, Denbighshire County Council. Bellows, C. E., has been appointed Controller of Technical Services and Surveyor to Hatfield Rural District Council. Bennett, J. M., formerly with Telford Development Corporation has taken up the post of Chief Assistant Materials Engineer with Lancashire County Council. Best, K. H., Partner with the firm of Husband & Co. has taken up a post with the firm of F. R. Bullen and Partners. Churchman, R. F., formerly with Berkshire County Council has been appointed Assistant Divisional Surveyor (Maintenance) with Buckinghamshire County Council. Darling, C. J., is now with the Bedfordshire Sub-Unit of the Eastern Road Construction Unit. Dight, C. J., has taken up the post of Assistant Engineer with Buckinghamshire County Council. Farrell, C. E., has taken up the post of Engineering Surveyor with the Main Roads Department, Government of Western Australia. Faulkner, A. J., is now with Cementation Construction Ltd., where he is employed as a Senior Engineer. Forshew, K., has taken up the post of Engineer with the Derbyshire County Council Sub-Unit of the Midland Road Construction Unit. Fox, E. L., has been appointed Senior Highway Maintenance Engineer with the firm of Messrs Kampsax of Copenhagen, Denmark, and will be working forthem in Afghanistan.
OF THE INSTITUTION OF HIGHWAY ENGINEERS 45

I

AUGUST 1970

I~

Institution Matters
Hampson. R. W .• has accepted the post of Computer Engineer with Hampshire County Council. He was previously employed as Assistant Engineer with Havant and Waterloo Urban District Council. Howarth. P. M .• has been promoted to Engineer with Livingston Development Corporation. Jones. V. E.• has taken up the post of Assistant County Surveyor (Planning and Traffic) with Hertfordshire County Council. Khatri. M. S .• has been appointed Senior Engineer (Highways) with the London Borough of Tower Hamlets. Matthews. G. W. A., retired from his post as Principal Highways Engineer, London Borough of Croydon, at the end of May. Matthews. R. G .• has been appointed Deputy Reclamation Officer to the recently formed Monmouthshire Derelict Land Reclamation Joint Committee. Nicholas. R. E., has been appointed Engineer and Surveyor Designate with Guisborough Urban District Council. Page, N .• has been promoted from Deputy Borough Engineer, Surveyor and Planning Officer with Ramsgate Borough Council to Borough Engineer with that authority. Patel, D. J., formerly with the Columbia Engineering Co. Ltd., Vancouver, Canada has taken up a post with the Department of Main Roads, Sydney, New South Wales. Patel. V. M., is now with the City Engineer's Department, Portsmouth City Corporation where he is employed as a Senior Assistant Engineer. Roberts. C, M., a Senior Partner with the firm of Sir William Halcrow and Partners retired at the end of April after 42 years service with the firm. Stanley. G. J .• has taken up the post of Civil Engineer with the Ministry of Public Building and Works. Waterworth, A., is now with the firm of Scott, Wilson, Kirkpatrick and Partners, in Nairobi, Kenya. Honours List published on the occasion of H.M. the Queen's official birthday on June 13th. During his career Mr Scott has served on many advisory and technical committees, and has been an active member of several professional organisations. He is a Past Chairman ofthe Northern Ireland Association of the Institution of Civil Engineers, a Past Chairman of the Northern Ireland Branch of the Institution of Municipal Engineers, and Founder Chairman of the Transportation Group of the Institution of Civil Engineers (Northern Ireland Branch). He was elected as a Member of the Institution in 1964 and was made a Fellow in 1966. When the Northern Ireland Branch was formed in 1964 he was the Founder Chairman. He was an Official Delegate to the P.I.A.R.C. Congress held in Rome in 1964 and he also visited the United States of America with the County Surveyors' Society Study Tour in 1965. As has already been reported, the Institution has sponsored a Conference in Belfast in July next year. Exceptionally, therefore, Mr Scott's Presidential Address will be delivered towards the end of his year of office, in conju nction with the Conference, probably on Monday 5th July, 1971.

C.B.
J. L. Paisley, (Chief Highway Engineer, Ministry of Transport). M.B.E. K. O. Martin, {Senior Engineer (Buildings), Public Works Department, Swaziland).

A.G.M. AND ELECTION
OF PRESIDENT
At the Annual General Meeting held on July 3rd, 1970 at the Institution of Structural Engineers, 11 Upper Belgrave Street, S.W.1, Mr Harold Kyle Scott, M.B.E., B.Sc., F.I.C.E., M.1. Mun.E., F.lnst.H.E., County Surveyor of Londonderry was elected President of the Institution in succession to Mr H. N. Ginns. Mr P. F. Stott, Joint Director, Planning and Transportation, Greater London Council, was elected as Senior Vice-President. Mr Scott was born in Maghera, County Londonderry, Northern Ireland and was educated at Rainey Endowed School, Magherafelt, and at Queen's University, Belfast, where he took a B.Sc. degree in Civil Engineering. H is first appointment came in 1932 as Assistant County Surveyor with Tyrone County Council.

JOINT MEETING ON LADY'SHARP'S REPORT
An audience of approximately one hundred attended a joint open discussion meeting, sponsored by the Institution in conjunction with the Town Planning Institute and the Institution of Municipal Engineers at Imperial College, London, S.W.7 on Friday. June 5th, 1970. The meeting discussed Lady Sharp's recent Report to the Minister of Transport on "Transport Planning; the Men for the Job", and some lively and informative comments were made. Mr P. F. Stott, Joint Director, Planning and Transportation, Greater London Council, a Vice-President of the Institution, led the small nominated discussion panel which consisted of . Mr J. D. Jones, Deputy Secretary, Ministry of Transport. Mr F.J. C. Amos, City Planning Officer, Liverpool City Corporation representing the Town Planning Institute and Mr H. D. Peake, Director of Technical Services, London Borough of Ealing, representing the Municipals. It is hoped to publish a detailed report of the discussion in a future issue of the Journal.

OBITUARY
Council learned with very much regret of the death of the fallowing: Mr L. 1. C. Beasley, (London, Member since 1959) Mr E. R. Henderson, (Newcastle upon Tyne, Associate Member si nee 1967) Mr G. M. Jones-Rees, (Carmarthenshire, Associate Member since 1950) Mr J. T. Knight, (Gloucestershire, Member since 1930) Mr W. J. Lewis, (Essex, Member since 1931 ). Mr. Harold Kyle Scott At the outbreak of World War II he volunteered for service in the armed forces and was appointed Garrison Engineer in the Northern Ireland Command. He obtained a Commission in the Royal Engineers in April, 1941 and in July of the following year was posted to Overseas Service in the Middle East where he served for almost four years mainly on Airfield Construction, attaining the rank of LieutenantColonel. In 1944 he was awarded the M.B.E. for his services. On demobilisation in the Spring of 1946 he was appointed, at the age of 33, to the post of County Surveyor of County Londonderry, a post which he still holds.
ENGINEERS

BIRTHDAY 1970

HONOURS

NORTHERN IRELAND BRANCH DINNER
Seventy-two members and their guests attended the Annual Dinner of the Northern Ireland Branch held at the Conway Hotel, Dunmurry, Belfast on Monday, May 18th, 1970.
AUGUST 1970

Council extends its congratulations to the following Members of the Institution on their inclusion in the Birthday
46 THE JOURNAL

OF THE INSTITUTION OF HIGHWAY

..~---------------------------------------:'-,

Institution Matters
The Toast of "The Institution" was proposed by the Rt. Hon. N. Q. Minford, M.P., Minister of State,' Ministry of Developme"nt. Northern Ireland. The Response was given by Dr. D. R. Sharp, M.B.E., a Vice. President-elect of the Institution, who was deputising for the President, Mr H. N. Ginns, who was unwell. The Branch Chairman, Mr J. r. Bill, a Director of John Graham (Dromore) Ltd., proposed the Toast of "The Guests" and the Response was given by Mr G. Burnison, Secretary of the Federation of Building Trade Employers of Northern Ireland. Amongst the guests attending were Mr H. K. Scott, County Surveyor of Londonderry and Senior Vice President of the Institution, Mr J. K. Ballantyne, Chairman, Northern Ireland Association ofthe Institution of Civil Engineers, Mr T. A. Warnock, Chairman of the Northern Ireland Branch of the Institution of Municipal Engineers, and the Secretary of the Institution, M r M. J Hall. Traffic Control", presented a situation report on the findings of area traffic control schemes throughout Europe and the United States and he brought out the real values and limitations which could be expected from such a scheme. Reference was made to the Glasgow Area Traffic Control Experiment where improvements were quoted at between 9 and 18 per cent and where an overaH benefit in economic return on the investment of the system of some 6,000 per cent had been attained. The discussion emphasised many aspects of area control and Mr Hillier gave detailed answers on many alternative systems. Herr Hans Barbe, consulting engineer of Zurich in a Paper entitled "Transportation Models as an Aid to the Traffic Engineer", brought a wideranging outlook to bear upon the present use of mathematical models for urban planning. He demonstrated that models could be both valuable tools and dangerous instruments. He admitted that the growing capacity of computer programs for transportation models had expanded the possibilities which could be examined, and therefore studies could grow in cost and length, rather than shrink. The discussion centred mainly around the existing use and future applications of model procedures. Herr Barbe confirmed that these, because of their use on an urban, subregional and regional scale represented considerable savings in cost over traditional survey methods. Mr A. P. Young, University of Salford, in his Paper on "Engineering for Public Transport" looked at the future trends in public transport and alternative systems under experimentation in the United States, Europe and Great Britain. He explained schemes being can. sidered for public transport in the United States and gave examples of multi-billion dollar programmes of research and construction to find effective solutions to the overall transportation problem. He issued a warning that in his view no new systems were attracting public transport and that rapid transit and track systems only fitted urban areas. The discussion centred on whether this country was yet ready to accept further developments in the public transport field beyond the need to provide for the essential or captive trips by public transport. Mr M. Milne, Director, SouthEastern Road Construction Unit and Mr F. D. J. Johnson, Branch Chairman each took the Chair for one of the two morning sessions, and Professor T. E. H. Williams, University of Southampton was in the Chairforthe first Paperofthe afternoon.
THE JOURNAL

CHANGE TO METRIC FABRIC REIN FORCEM ENT
After consultation with the Reinforcement Manufacturers Association, the British Standards Institution decided last year not to withdraw BS 12211964 (imperial units) on 31st December 1969 as originally planned. The RMA pointed out that there was then clear evidence that a substantial demand for imperial fabrics still existed, both from consulting engineers and contractors. It seemed, therefore, in the best interests of customers to run both imperial and metric fabrics for a further period, and the RMA was able to meet this need. BS 4483 (metric units), published in August 1969, has now gained wide acceptance, and manufacturers can no longer produce both ranges. Accordingly, the BSI withdrew BS 1221 on 30th June 1970 simultaneously with all other British Standards (imperial units) covering steel for the reinforcement of concrete.

SOUTHERN BRANCH TRAFFIC ENGINEERING SYMPOSIUM
A one-day symposium on "Traffic Engineering - Engineering for Traffic" was held at Southampton University on Friday, April 24th, 1970 and 130 delegates attended. Four Papers were presented and each was followed by a lively and informative discussion period. In his Paper on "Traffic Planning in Urban Areas", Mr G. K. Benn, City of Westminster, stressed the need for professional integration in the joint task of urban planning and he em. phasised that the traffic problem needed to be quantified before development plans were made. The use of certain criteria was recommended and these included the limitation or restraint of traffic in residential areas by some mechanism which, whilst allowing facilities for residents, still allowed for improvements in the capacity, the main "traffic controls" and safety of junctions and improved public transport and reduced private commuting where possible. Two major points emerged from the discussion, the location of precincts and pedestrian areas and the need for their selection before the appraisal of the traffic plan, and whether the "traffic corridor" concept proposed by Mr Benn should be reconsidered in the light of the possible impact of traffic on properties and environment within busy areas. Mr J. A. Hiller, Road Research Laboratory, in his Paper on "Area
AUGUST 1970

THE CONCRETE SOCIETY 1970 AWARD
A group of buildings comprising a new headquarters building for the entire Academy and a new building to accommodate one college, at the Royal Military Academy, Sandhurst, has won the Concrete Society 1970 Award. The architects for the winning entry were Gollins, Melvin, Ward and Partners in conjunction with the Ministry of Public Building and Works for the Ministry of Defence, the consulting engineers were Scott Wilson Kirkpatrick and Partners and the contractors were Higgs and Hill (Building) Ltd. The judges, The Viscount Esher, Past President of the RI BA, representing the President of the Royal Institute of British Architects, Mr A. A. Fulton, President of the Institution of Civil Engineers and Dr D. D. Matthews, Past President of the Institution of Structural Engineers, representing the President of the Concrete Society, also selected two entries for Certificates of Commendation and mentioned eight other entries in their report. Of the 130 entries the judges were unanimous and unreserved in selecting for its outstanding excellence in the use of concrete the group of buildings at the Royal Military Academy, Sandhurst. Of the scheme they said: "The differing site levels have been exploited to improve the proportions of the structure, so that it achieves a measure of real nobility. The simple and successful use of light and dark toned precast concrete elements and the unaffected detailing ..... are notable ["
OF HIGHWAY ENGINEERS -47

OF THE INSTITUTION

Institution Matters
The Award is in the form of a plaque which will be fixed to the winning structure, and certificates presented to those principally concerned with its design and construction. The presentation was made by the Rt. Hon. Duncan Sandys, President of the Civic Trust, at a special dinner held in London on Thursday, 9th July. tion of capital money. But what about running costs? For the 400W MBF/U lamp (and the 135W SOX) shown in Table 3 of the Paper the cost of lamps alone over the 20 years lifetime of the installation exceeds the initial capital cost. In fact if the replacement period were extended from Mr Cox's 4,000 hours by a mere 2,000 hours to, 6,000 hours, enough money would be saved to install two extra lighting points. The extra light produced by these points would permit further savings to be made in cleaning costs without sacrificing any of the standards that we are all anxious to maintain. But Mr Cox would call this over-design. Orwould he? Yours faithfully, Deputy Director, J. A. Green Local Government Operational Research Unit.

THE ASSOCIATION OF HIGHWAYTECHNICIANS
Total Membershiptodate896 5th JUNE. 1970

. !

ELECTED TO MEMBERSHIP Anderson, R. J. (Assistant Engineer,

Zetland C.C.). Bedford, J. H. (Programming Assistant, Lindsey C.C.). Beveridge, J. (Technical Assistant, LETTER TO THE EDITOR Elgin Burgh Council). Street lighting Burrows, D. R. (Assistant Divisional Surveyor, Cornwall C.C.). Sir - I was aggrieved to read in the May, 1970 issue of the Journal the Burt. D. J. G. (Assistant Engineer, Egham U.D.C.). remarks attributed to Mr K. T. O. Cox at Callingham, M. J. (Assistant Engithe close of this discussion on his neer, Egham U.D.C.). Paper "Street Lighting" presented at Chandler, S. (Higher Technician, your National Conference in DecemHerts. C.C.). ber, 1969. While recognising that Cope, A. J. (Inspector of Works, comments made on a Conference Crown Agents). platform can be ill-judged, I find little Craven, B. T. (Civil Engineering evidence in Mr Cox's Paper to support Mr Cox replies: I am sorry that Mr Technician, Lindsey C.C.) .. his assertion that he does not need the Green is so aggrieved. If the whole Delderfield,' J. C. (Surveyor/ kind of advice offered by this Unit. issue turns on the mortality curve, let Draughtsman, London Borough of In his reply to Col. F. E. Ladly's us look at some of those given in the Havering) . comment, Mr Cox is reported as saying local Government Operational ReDe Silva, P. G. (Engineering Assis"of course it is economic for group search Unit report. tant (Road Construction), Bintang lamp replacement to be done in excess Mean mortality/ Bahru Sdn Bhd. Malaysia). of 9,000 hours burning". There is no 1000 hrs. Dronfield, G. P. (Assistant Divisional "of course" about it, Mr Cox. In one Surveyor, Cornwall C.C.). phrase you dismiss the entire theory Up to After Kalinde, H. A. (Soils Technician, and practice of preventive replacement. 4000 4000 Brian Colquhoun, Hugh O'Donnell & Perhaps you were just trying to score hrs. hrs. Partners, Malawi). points off the U nit. for in your Paper, per cent per cent King, A. J. (Works Superintendent, under the heading 'lamp Replacement', Fig.2 (60W SOX) 5.75 10 P.W.D., Sarawak). you say "Figure 3 shows the steepen5.1 Kuhn. H. A. (Branch Manager, ing mortality curve after 4,000 hours Fig.4 (150W SOX) 2.75 Fig.5 (140W SLI) 3.0 5.5 Petrocol Ltd.). operation. This means increasingly Fig.S Langstaff. W. (Technical Officer. frequent visits to replace scattered (125W MBF/U) 3.25 5.75 The Eskett Limestone Quarries Ltd.). lamp failures with a consequent unFig.10 Leebetter, M. J. (Police Inspector. economic use of labour and equip(400W MBF/U) 2.0 3.25 New Scotland Yard). ment." Evidently the principles of Mahomed. I. I. (Senior Materials preventive replacement, and the fact No pronounced steepening, Mr Green? that unit costs rise again when a certain My mortality curve was derived from Technician, W. & C.. French (Malawi) Ltd.). replacement interval is exceeded, are data available from the major lamp Meek, A. J. (Engineering Assistant, well known to you. manufacturers. Those in the report Hereford City C.). were taken from three lighting authThe whole issueturnson the mortality Mumby, D. H. (Laboratory Techcurve. In our report, of which Mr Cox orities only and show marked disnician, Tarmac (Scunthorpe) Ltd.). thinks so little, we show actual morparities. Oates, D. S. (Traffic Assistant, East Yes, I am concerned with capital tality curves for actual lamps under Sussex C.C.). costs and one reason is that their actual conditions in actual local authPorter, D. P. (Surfacing Supervisor, amortisation is properly a part of the orities. We found no pronounced annual cost of an installation. Table 3 Tarmac Roadstone Holdings Ltd.). steepening. Pyatt, F. S. A. (Inspector of Works. of the Paper shows that loan repayWhere did Mr Cox get his mortality Kent C.C.). ments can add another 70 per cent to curve? Rowntree. A. L (Laboratory TechThe value of wasted light also what are frequently taken as "running nician, Cumberland C.C.). attracts Mr Cox's attention and he costs" . Stark, D. J. (Engineering Assistant, As lamp development continues, seems to imply that the Unit advocates Truro City C.). both mortality and lumen maintenance street lighting based on worn out D. A. (District Technical curves will flatten out and a longer Tunstall. lamps. This is quite untrue. Officer, E.C.C. Quarries Ltd.). Mr Cox is preoccupied with the period may elapse between. group Turner, M. H. (Civil Engineering capital cost of installations. Indeed, at replacements, but, for an efficient S.E.R.C.U. lighting installation, I suggest that a Technician/Draughtsman, the end of his Paper he poses two (Hants. C.C. Sub-Unit)). 9000 hour period is a long way off. questions about the effective utilisa-

48

THE JOURNAL

OF THE INSTITUTION

OF HIGHWAY

ENGINEERS

AUGUST 1970

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DOCUMENT INFO
Description: Includes topics regarding Review of Small Span Highway Bridge Design and Standardisation, The Analysis and Design of Short Span Skew Highway Bridge Slabs, The Effect of Work Study and Financial Incentives in Highway Maintenance, etc..