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20320140503002-2

VIEWS: 2 PAGES: 8

									 International Journal of Civil              and             (IJCIET),
INTERNATIONALEngineeringMarchTechnologyCIVIL ISSN 0976 – 6308 (Print),
                                 JOURNAL OF 15-22 © IAEME
 ISSN 0976 – 6316(Online) Volume 5, Issue 3,     (2014), pp.
                                                                       ENGINEERING
                      AND TECHNOLOGY (IJCIET)
ISSN 0976 – 6308 (Print)
ISSN 0976 – 6316(Online)                                                          IJCIET
Volume 5, Issue 3, March (2014), pp. 15-22
© IAEME: www.iaeme.com/ijciet.asp
Journal Impact Factor (2014): 7.9290 (Calculated by GISI)
                                                                                  ©IAEME
www.jifactor.com




     PERFORMANCE OF LATERAL SYSTEMS IN TALL BUILDINGS FOR
                     VARYING SOIL TYPES

             *Mohamed Fadil Kholo Mokin1, R.K.Pandey1, Prabhat Kumar Sinha2
                                   1
                                 Department of Civil Engineering,
                  Sam Higginbottom Institute of Agriculture, Technology & Sciences
                    (Formerly Allahabad Agricultural Institute), Allahabad, India
                             2
                               Department of Mechanical Engineering,
                  Sam Higginbottom Institute of Agriculture, Technology & Sciences
                    (Formerly Allahabad Agricultural Institute), Allahabad, India


 ABSTRACT

         Efficient lateral systems, decreases the lateral deformations caused by the seismic forces in
 the buildings. In this work, it is proposed to carry out an analytical study, on multistory buildings of
 10, 20 and 30 stories, was carried out accounting for different seismic zones and soil types. The
 suitability and efficiency of different lateral bracing systems that are commonly used and also that of
 concrete in fills are investigated. The different bracing systems viz., X-brace, V-brace, inverted V or
 Chevron brace, Outriggers and in fills, are introduced in the buildings through analytical models.
 These building models were analyzed, using ETABS software, for the action of lateral forces
 employing linear static and linear dynamic methods as per IS 1893 (Part I): 2002. The results of the
 analyses, in terms of lateral deformations and base shears, were obtained for all the different
 conditions discussed above The suitability of the types of lateral system for the buildings is
 suggested based on the soil type.

 Keywords: Tall buildings, Bracings, Type of Soils, Seismic coefficient method, Response spectrum
 method, Time History Method.

 1. INTRODUCTION

         Mankind has always had a fascination for height and throughout our history; we have
 constantly sought to metaphorically reach for the stars. The design of skyscrapers is usually
 governed by the lateral loads imposed on the structure. As buildings have taller and narrower, the
 structural engineer has been increasingly challenged to meet the imposed drift requirements while

                                                   15
International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print),
ISSN 0976 – 6316(Online) Volume 5, Issue 3, March (2014), pp. 15-22 © IAEME

  inimizing
minimizing the architectural impact of the structure. In response to this challenge, the profession has
proposed a multitude of lateral schemes that are now spoken in tall buildings across the globe.
                                                                   different
        This study seeks to understand the evolution of the different lateral systems that have
                                                                                     he
emerged and its associated structural behavior for different types of soil types. The different type of
bracings are introduced in RCC building model at the same location to understand the suitability of
                    espect
the systems with respect to the seismic motions. While other properties of the structural members in
the building is remain constants such as the size of the columns, beams, bracings and thickness of
                                                                           soils. Analytical modeling is
slabs. This study is done under considering the IS code for different soils. Analyt
                  .
done in ETABS. The major goal is to appraise the lateral deformations occurs by considering the
above parameters.
The seismic motion that reaches a structure on the surface of the earth is influenced by the local soil
conditions. Greater structural distress is likely to occur when the period of the underlying soil is
close to the fundamental period of the structure. Tall buildings tend to experience greater structural
                                                                      motion
damage when they are located on soils having a long period of motion because of the resonance
effect that develops between the structure and the underlying soils. If a building resonates in
response to ground motion, its acceleration is amplified. It is possible that a number of underlying
                           riod
soils layers can have a period similar to period of vibration of the structure. As per IS 1893 (Part I) –
2002, soils classification can be taken as Type – I, Rock or Hard soil: Well graded gravel and sand
mixtures with or without clay binder and clayey sands poorly graded or sand clay mixtures, whose N
(standard penetration value) should be above 30. Type – II, Medium soils: All soils with N between
10 and 30, and poorly- graded sands or gravelly sands with little or no fines. Type – III, Soft Soils:
All soils other than whose N is less than 10.

2. ANALYTICAL MODELLING

        A plan of 36mx36m is taken into consideration having 6mx6m bays on both the sides. The
different types of Bracings (X,V, Inverted V), Outriggers, Infills are introduced in the system at
center in 2 bays . The floor height is taken as 3m for all the models. The plan and elevation is shown.




                                                PLAN

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International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print),
ISSN 0976 – 6316(Online) Volume 5, Issue 3, March (2014), pp. 15-22 © IAEME




        Model 1          Model 2         Model 3           Model 4         Model 5

3. BUILDING DIMENSIONS

        The building is 36m x 36m in plan with columns spaced at 6m from center to center. A floor
to floor height of 3.0m is assumed. The variation is considered in different types of soils.

Structural systems of the Building:
                      Slab thickness                       115 mm
                      Beam dimensions               350 mm x 450 mm
                      Column dimensions             600mm x 600mm
                      Brace Members size               230mm x 230 mm
                      Infills Wall Thickness               250 mm
                      Grade of Concete and
                                                     M20 concrete, Tor steel
                      Steel

                              Table: Design Variable for analysis
                     Design variable           Value             Reference
                  Dead loads
                  (a)Masonry                 20 kN/m3       IS 875:1987(part 1)
                  (b) Concrete               25 kN/m3
                  Live loads
                                              4kN/m2
                  (a) Floor load                            IS 875:1987(part 2)
                                             2.0kN/m2
                  (b) Roof load
                                             1.0kN/m2
                  (c) Floor Finishes
                  Importance factor             1.0         IS 1893:2002
                  Response Reduction
                                                 5          IS 1893:2002
                  Factor

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International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print),
ISSN 0976 – 6316(Online) Volume 5, Issue 3, March (2014), pp. 15-22 © IAEME

      The Static load case, viz., seismic coefficient method, and the Dynamic load case, viz.,
Response spectrum method is adopted along with different loading combinations discussed.

3.1 Equivalent lateral force
        Seismic analyses of most of the structures are still carried out on the basis of lateral
(horizontal force assumed to be equivalent to the actual (dynamic) loading. The base shear which is
the total horizontal force on the structure is calculated on the basis of structure mass and fundamental
period of vibration and corresponding mode shape. The base shear is distributed along the height of
structures in terms of lateral forces according to code formula.

3.2 Response Spectrum Analysis
        This method is applicable for those structures where modes other than the fundamental one
significantly the response of the structure. In this method the response of Multi-Degree-of –Freedom
(MDOF) system is expressed as the superposition of modal response, each modal response being
determined from the spectral analysis of single-degree-of-freedom (SDOF) system, which is then
combined to compute the total response. Modal analysis leads to the response history of the
structure to a specified ground motion; however, the method is usually used in conjunction with a
response spectrum.

4. OPTIMUM LOCATION OF BRACES IN BUILDING MODEL

        To obtain the optimum location of braces in building model, braces are introduce in the
different bays in the elevation of the building model in all the direction symmetrically, i.e., the braces
are introduced in bays of the building model in outer periphery symmetrically. As the plan of size
36m x 36m is taken having 6 bays of 6m length in each direction. The outer frame is taken and
braces are introduce in 1st bay in both sides from center of the frame, then in 2nd bay in both sides
from center of the frame and then in the 3rd bay in both sides from the center. The results of the
deflection are shown in below table.

                                 Location of Brace             Max.
                               (bay–bay from center)       Displacement
                                                           (lateral) mm
                               Bay (1-1 from center)           168.4

                               Bay (2-2 from center)           159.6

                               Bay (3-3 from center)           145.3



       From the above table it is found that by introducing the brace in the centre position shows the
minimum value for displacement as compared with other locations. Hence the braces will be
introduces in the center location in all building frame in all direction in elevation to have minimum
displacements, then these models are analyzed for the objective




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International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print),
ISSN 0976 – 6316(Online) Volume 5, Issue 3, March (2014), pp. 15-22 © IAEME

5. RESULTS

            CASE 2: THE ROOF DISPLACEMENT WITH RESPECT TO SOIL TYPES
                                              ROOF DISPLACEMENTS
                        WITHOUT
            SOIL          BRACE        X-BRACE         V-BRACE       INV V-BRACE      OUTRIGGERS          INFILLS
 STRY.      TYPE      STAT.   DYN.   STAT.  DYN.     STAT.  DYN.     STAT.   DYN.     STAT.  DYN.      STAT.   DYN.
   10         I        31.4   22.2    22.7   16.3     23.3   16.7     22.7   16.3      19.8  14.5       16.7    12.1
             II        42.7   30.2    30.9   22.1     31.7   22.7     30.9   22.1      26.9  19.7       16.6    16.6
             III       52.4     37    37.9   27.1     38.9   27.8     37.9   27.1      33.1  24.2       27.9    20.2

  20          I       65.5    44.9    53.2    36.8    53.8    37.2    52.9     36.6    47.9     33.9    46.7    31.3
             II       89.1    89.1    72.3    50.1    73.2    50.7    71.9     49.9    65.2     46.1    63.6    42.5
             III      109.5   77.2    88.8    61.5     90     62.2    88.3     61.2    80.1     56.7    78.1    52.1

  30        I      126.8   88.3      86.9     59.3    87.5   59.8       86.5    59     80.6    55.6    80.8     53.5
            II     172.5   120.1    118.3     80.6   119.1   81.4      117.7   80.3    109.8   75.8     110     72.7
           III     211.9   147.5    145.3      99    146.3   100       144.6   98.7    134.9   93.1    135.1    89.3
NOTE : ALL UNITS ARE IN MM ; I = HARD SOIL ; II = MEDIUM SOIL ; III = SOFT SOIL AS PER IS CODE .


       The deflection in the soft soil is higher when compared to all other soils types i.e. hard rock
and medium soil, while the height of the buildings has a impact on the deflection to be higher. As
discussed in the previous case the roof displacement obtained in the static method is greater than the
displacements obtained in the response spectrum method.

         CASE 3: THE ROOF DISPLACEMENT VS THE HEIGHT OF THE BUILDING.
                                                  LATERAL DISPLACEMENTS
  STOREY            WITHOUT BRACE               X-BRACE          OUTRIGGERS                          INFILLS
                   STATIC  DYNAMIC       STATIC DYNAMIC       STATIC   DYNAMIC                STATIC     DYNAMIC
        0             0         0            0         0         0         0                     0            0
        1            3.8       3.3          2.9       2.7       3.1       2.8                   3.0          3.0
        2            11.1     9.6           7.0       6.4       7.3       6.6                   5.6          5.2
        3            19.6     16.7         11.2       9.9       11.6     10.3                   8.0          7.0
        4            28.4     24.1         15.7       13.6      16.2     14.1                   10.9         9.1
        5            37.4     31.4         20.4       17.4      21.0     18.0                   14.1        11.5
        6            46.4     38.6         25.4       21.3      26.1     21.9                   17.8        14.0
        7            55.5     45.7         30.7       25.2      31.4     25.9                   21.7        16.8
        8            64.6     52.6         36.1       29.1      36.8     29.9                   25.9        19.6
        9            73.7     59.4         41.7       33.1      42.4     33.9                   30.4        22.6
       10            82.8     66.0         47.4       37.0      48.0     37.8                   35.1        25.7
       11            91.8     72.5         53.2       40.9      53.7     41.7                   39.9        28.9
       12           100.7     78.7         59.0       44.8      59.3     45.6                   44.9        32.1
       13           109.5     84.8         64.9       48.6      65.0     49.4                   50.0        35.4
       14           118.2     90.7         70.7       52.4      70.5     53.1                   55.3        38.7
       15           126.7     96.3         76.6       56.2      72.3     54.1                   60.5        42.0
       16           135.1    101.7         82.4       59.8      77.5     57.5                   65.8        45.3
       17           143.2    106.9         88.1       63.4      83.0     60.9                   71.2        48.6
       18           151.1    111.9         93.7       66.9      88.3     64.3                   76.5        51.9
       19           158.7    116.5         99.2       70.3      93.6     67.5                   81.8        55.2
       20           166.0    121.0        104.6       73.6      98.7     70.7                   87.0        58.5
       21           172.9    125.1        109.8       76.8     103.7     73.5                   92.2        61.7
       22           179.4    128.9        114.8       79.9     108.5     76.7                   97.4        65.0
       23           185.5    132.5        119.5       82.8     113.0     79.5                  102.4        68.2
       24           191.1    135.7        124.1       85.6     117.3     82.1                  107.4        71.3
       25           196.1    138.6        128.4       88.3     121.4     84.7                  112.3        74.5
       26           200.6    141.1        132.4       90.8     125.1     87.0                  117.1        77.6
       27           204.4    143.3        136.1       93.2     128.6     89.2                  121.8        80.6
       28           207.6    145.1        139.6       95.4     131.8     91.2                  126.4        83.7
       29           210.1    146.6        142.8       97.5     134.6     93.2                  131.0        86.7
       30           211.9    147.5        145.3       99.0     134.9     93.1                  135.1        89.3


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International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print),
ISSN 0976 – 6316(Online) Volume 5, Issue 3, March (2014), pp. 15-22 © IAEME

        For 10 storey building model, it is found as the Infills are most effective against the lateral
displacement then comes Outrigger system then come Braced system, when compared with normal
bare frame model. The velocity and the acceleration values are found to be increasing in infills,
outriggers, bracing systems respectively.
        For 30 storey building model, it is found as the Infills system and Brace system are most
effective to withstand the time history function against displacements. The difference of
displacements in normal bare frame model and the lateral system building models are found to be
less. This indicates that the effect of lateral systems are not much effective with the increase in the
height of the buiding model for this time history loading. This is due to the infills are predominant
upto certain height and after this it reacts in a negative way while attractive the inertia forces hence
increasing the lateral displacements.

CASE 5: LATERAL STOREY DRIFT WITH RESPECT TO HEIGHT OF THE BUILDING.
                                             LATERAL DRIFTS
 STORE      WITHOUT BRACE               X-BRACE          OUTRIGGERS                     INFILLS
   Y               DYNAMI          STATI    DYNAMI              DYNAMI                      DYNAMI
           STATIC      C             C         C     STATIC        C              STATIC        C
   0          0        0             0         0         0         0                 0          0
   1         3.8      3.3           2.9       2.7       3.1       2.8               3.0        3.0
   2         7.3      6.3           4.1       3.7       4.2       3.8               2.6        2.2
   3         8.5      7.1           4.2       3.5       4.3       3.7               2.4        1.8
   4         8.8      7.4           4.5       3.7       4.6       3.8               2.9        2.1
   5         9.0      7.3           4.7       3.8       4.8       3.9               3.2        2.4
   6         9.0      7.2           5.0       3.9       5.1       3.9               3.7        2.5
   7         9.1      7.1           5.3       3.9       5.3       4.0               3.9        2.8
   8         9.1      6.9           5.4       3.9       5.4       4.0               4.2        2.8
   9         9.1      6.8           5.6       4.0       5.6       4.0               4.5        3.0
   10        9.1      6.6           5.7       3.9       5.6       3.9               4.7        3.1
   11        9.0      6.5           5.8       3.9       5.7       3.9               4.8        3.2
   12        8.9      6.2           5.8       3.9       5.6       3.9               5.0        3.2
   13        8.8      6.1           5.9       3.8       5.7       3.8               5.1        3.3
   14        8.7      5.9           5.8       3.8       5.5       3.7               5.3        3.3
   15        8.5      5.6           5.9       3.8       1.8       1.0               5.2        3.3
   16        8.4      5.4           5.8       3.6       5.2       3.4               5.3        3.3
   17        8.1      5.2           5.7       3.6       5.5       3.4               5.4        3.3
   18        7.9       5            5.6       3.5       5.3       3.4               5.3        3.3
   19        7.6      4.6           5.5       3.4       5.3       3.2               5.3        3.3
   20        7.3      4.5           5.4       3.3       5.1       3.2               5.2        3.3
   21        6.9      4.1           5.2       3.2       5.0       2.8               5.2        3.2
   22        6.5      3.8            5        3.1       4.8       3.2               5.2        3.3
   23        6.1      3.6           4.7       2.9       4.5       2.8               5.0        3.2
   24        5.6      3.2           4.6       2.8       4.3       2.6                5         3.1
   25         5       2.9           4.3       2.7       4.1       2.6               4.9        3.2
   26        4.5      2.5            4        2.5       3.7       2.3               4.8        3.1
   27        3.8      2.2           3.7       2.4       3.5       2.2               4.7         3
   28        3.2      1.8           3.5       2.2       3.2        2                4.6        3.1
   29        2.5      1.5           3.2       2.1       2.8        2                4.6         3
   30        1.8      0.9           2.5       1.5       0.3        0                4.1        2.6
                                   NOTE: ALL UNITS ARE IN 'mm'.




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International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print),
ISSN 0976 – 6316(Online) Volume 5, Issue 3, March (2014), pp. 15-22 © IAEME

5. CONCLUSIONS

Based on the study of analysis of results the following conclusions are drawn

 (a) The structural performance among three bracing systems (X-brace, V-brace, Inverted V-
     brace), one outrigger system (introduced at Top and Middle levels), one infill system
     (introduced at the place of braces), the variation of displacement is smaller in infill system.
     This statement is true in all the zones for all the soil conditions and for different loading
     conditions.
 (b) The values of displacements and base shears obtained in X-Brace, V-Brace and Chevron
     Brace structure models, does not shows much variations, these values are found to be almost
     identical, this statement is true in all types of soils, for different heights and for all loading
     conditions.
 (c) The sudden variation in the storey drift is seen at the location of the outriggers in the building
     models. At the storey where outrigger placed observed to be more stiff than other stories.
 (d) With the provisions of Infills and Bracings in the analytical models, Time Period of the
     structures are found to be lesser in these models when compared to Bare frame system.

6. REFERENCES

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 2. Huanjun Jiang, Bo Fu and Laoer Liu, “Seismic Perfromance Evaluation of a Steel-
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International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print),
ISSN 0976 – 6316(Online) Volume 5, Issue 3, March (2014), pp. 15-22 © IAEME

 12. IS -1893, “Criteria for Earthquake Resistant Design of Structures – Part I, General provisions
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