Tilt Up Constructions

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					Seminar Report 2007-08


                                   ABSTRACT

        The paper deals with the salient features of tilt –up construction and the delicate
ways by which it can be applied to the present construction scenario. It describes the
potential of tilt - up concrete construction technique as a viable alternative to
conventional methods of construction under favorite conditions. It also establishes the
fact that tilt- up (also called tilt wall) concrete construction is finding its way among its
competitors in the fiercely competitive field of construction methods. This highly
efficient, practical method of construction makes beautiful buildings possible at costs that
rival the most utilitarian industrial building. Tilt-up contractors are innovative, and
continually work to improve Tilt-up techniques. Today, there are many contractors are
experts in this specialized construction. Design-build construction scheduling further
enhances the Tilt-Up concept! The use of computers in the preplanning and layout
process provides the opportunity to make innovative improvements before the design is
finalized.




Dept. of Civil Engineering                    i            Govt. College of Engg., Kannur
Seminar Report 2007-08



                             CONTENTS


1. INTRODUCTION                                                 1
2. EVOLUTION OF TILT-UP                                         2
3. CONSTRUCTION PROCEDURE                                       3
4. CONSTRUCTION DETAILS                                         6
       4.1 FOOTING AND FLOOR SLABS                              6
       4.2 TILT-UP PANELS                                       8
       4.3 REINFORCEMENT                                        13
       4.4 EMBEDS AND INSERTS                                   15
       4.5 CONCRETE PLACEMENT                                   15
       4.6 PANEL ERECTION                                       16
       4.7 PANEL FINISHING                                      19
       4.8 INSULATING THE PANELS                                20
5. FIRE RESISTANCE OF TILT UP PANEL                             21
6. ADVANTAGES OF TILT-UP                                        22
7. INTEGRALLY COLOURED TILT-UP CONCRETE                         23
8. STEEL AND TILT-UP TOGETHER: USING THE STRENGTHS OF EACH 24
9. PRECAST AND TILT-UP CONCRETE                                 24
10. SITE CONDITIONS THAT LIMIT TILT-UP                          25
11. CONCLUSION                                                  26
   REFERENCES                                                   27




Dept. of Civil Engineering         ii     Govt. College of Engg., Kannur
Seminar Report 2007-08


1. INTRODUCTION
       Tilt up concrete construction, which began in southern California in the late
1950‟s as an economical and fast way to construct concrete walls for ware houses, has
become today a multi-billion dollar industry, accounting for over 10,000 buildings
annually. It is now used for shopping centers, distribution facilities, ware house,
manufacturing plants, office buildings, prisons, schools, churches, and nearly every type
of one to four-storey building. According to a survey by the tilt wall concrete association,
over 300 million square feet of tilt wall buildings were constructed in 1999.

       The term tilt wall was coined in the late 1950‟s to describe a method for
constructing concrete walls rapidly and economically without the formwork necessary for
poured-in-place walls. Simply, it is a two-step process: First, slabs of concrete, which will
comprise sections of wall, are cast horizontally on the building floor slab, or separate
casting slab. Then, after attaining proper strength, they are lifted (tilted) with a crane and
set on prepared foundations to form the exterior walls.

   When they have attained sufficient strength, usually a week to 10 days, a mobile truck
crane is brought to the job site to lift and set them on prepared foundations. The erected
panels are temporarily braced, connected, and the joints between them caulked. The roof
structure is then constructed and attached to the walls to complete the building shell.
Techniques continue to improve as new innovations and research evolve, furthering the
advantages and economics of tilt-up, and as information about tilt-up is more widely
available, tilt-up is attracting worldwide attention and activity. For architectural
attractiveness, the architect has almost unlimited freedom to arrange and assemble the
panels, plus a wide choice of surface finishes, to achieve what are often award-winning
designs. Construction time for a tilt-up building, from completion of the floor slab to
completion of the building shell, is often less than four weeks.




Dept. of Civil Engineering                    1             Govt. College of Engg., Kannur
Seminar Report 2007-08


2. EVOLUTION OF TILT –UP CONSTRUCTION
           Tilt wall is a simple concept. Its origin may have been 2,000 years ago when some
    anonymous roman builder discovered it would be easier to cast a slab of concrete on
    the ground then hoist (tilt) it up into position, than to build two wood forms, place
    concrete between them, and then remove the forms.

           Tilt wall, as we know it today, evolved from such early innovations, and
undoubtedly during the history of concrete construction has had many applications.
However its feasibility for constructing large thin wall panels had to await reinforced
concrete, which came into use in the early1900‟s.

           Credit for one of the first reinforced concrete site-cast walls that was cast
horizontally then tilted up, goes, according to the archives of the Portland Cement
Association, to an innovative builder, Robert Aiken. In about 1908 he constructed several
buildings using lifting jacks or derricks to raise the panels. One of the buildings was a
two-storey warehouse at Camp Logan, Illinois, another at Camp Perry, Ohio. He also
reportedly constructed a Methodist Church in Zion. In Chicago, in about 1912, a four-
storey factory was reportedly constructed using a derrick to raise the concrete walls.

           But the popularization of tilt wall had to wait for the one essential element
necessary to turn it into a fast, economical production method: the mobile truck crane.
These became available in the late 1940‟s, at the close of World War II. Another essential
for on-site construction was availability of ready-mixed concrete, introduced a few years
earlier.

           With the availability of truck cranes and ready-mixed concrete, a third fortuitous
condition was present: a post-WWII pent-up demand for new construction, including
warehouses and manufacturing plants. These were ideally suited for tilt wall, with long,
nearly windowless walls, and repetitive panels. Some anonymous contractor (or
contractors) cautiously tried the method, it worked, and the tilt wall industry was born.

           Over the years innovative architects, engineers, contractors, and hardware
vendors, have contributed numerous refinements in design and construction methods,
resulting not only in award winning architectural designs, but improved design and
construction methods, making possible very tall panels (forty feet high is not uncommon),


Dept. of Civil Engineering                     2             Govt. College of Engg., Kannur
Seminar Report 2007-08


faster erection time (lifting, setting, and bracing 20-30 panels a day is commonplace,
achieved through well-trained crews and innovative ground-release lift attachments), and
a wide choice of finishes available for architectural attractiveness (such as patterned form
liners used as a casting surface, resulting in a textured exterior surface).

       Tilt wall construction is most frequently used for one-storey commercial buildings
such as warehouses or office buildings, though two, three and four storey office buildings
are becoming commonplace. Condominiums and hotels as tall as ten stories have been
constructed with tilt wall concrete. However, tilt wall concrete is no longer limited to use
in industrial and commercial buildings. In 1993, tilt wall concrete panels were used to
construct trickling filter tanks at a wastewater treatment plant.



3. CONSTRUCTION PROCEDURE
   Brief descriptions of the six steps involved in the construction of tilt wall building are
as follows: -

       1. First, the concrete floor slab (as shown in figure1.), which will serve as a
           casting base for the panels, is placed on the prepared sub grade. At least a five-
           inch thick slab on a well-compacted sub base is essential. The slab is held
           back several feet around its perimeter to allow space for setting wall panels,
           which will be later, filled in with concrete. At the same time, the perimeter
           foundations are constructed, upon which the wall panels will be set.
       2. The wall construction process begins with laying out the panels on the floor
           and constructing the perimeter forms. Forms are typically dimensioning
           lumber, making the panels 0.1397m, 0.18415m or 0.23495m thick




                              Fig. 1. Wall panel cast on floor.


Dept. of Civil Engineering                     3             Govt. College of Engg., Kannur
Seminar Report 2007-08


       3. With the edge forms in place, door and window openings are blocked out and
           set in place, reinforcing added (typically #4 bars at 0.45m on center
           horizontally and #5 bars at 0.3m on center vertically, all placed at the panel
           center for equal bending resistance the greater reinforcing is used vertically
           since most panels are designed to span vertically from floor to roof),
           placement of embedded items, such as for attaching the lifting cables, are put
           into place.
       4. Concrete is placed in the forms; finished, cured, and let set for 5 – 10 days
           while the concrete attains sufficient strength for lifting.
       5. On lifting day, cables are attached to inserts cast into the panels and the crane
           lifts each panel in sequence and sets it on the prepared foundation, proceeding
           around the building perimeter. Before releasing each panel, temporary braces
           are installed (at least two per panel) to brace the panel until the roof structure
           is attached. An experienced rigging crew can erect 30 or more panels in a day
           usually enough to complete a building enclosure (as shown in figure 2).




                               Fig. 2. Crane lifts the panel.




6. Connections between panels are made (usually by welded splices of steel ledger
angles), joints between panels (typically 0.01905meter) are caulked, patching is done if
necessary to repair blemishes; concrete is placed in the closure strip between the panels
and the floor slab (usually a two foot wide strip); and the bracing is removed when the
roof has been permanently connected to the walls as shown in figure 3.




Dept. of Civil Engineering                    4              Govt. College of Engg., Kannur
Seminar Report 2007-08




                             Fig. 3. Temporary bracing in place.




                             Fig. 4. Roof structure erected.




CONSTRUCTION PICTURES




   Fig. 5. Forming panels on           Fig. 6.Panel with         Fig. 7.Placing concrete in
         the floor slab           reinforcing and ready for                panels
                                         concreting




Dept. of Civil Engineering                 5             Govt. College of Engg., Kannur
Seminar Report 2007-08




                                                  [




     Fig. 8. Lifting a panel
                                   Fig. 9Panel bracing prior to          Fig.10.Construction
                                    roof structure installation              progressing




4. CONSTRUCTION DETAILS

4.1 FOOTINGS AND FLOOR SLABS

             Once planning is complete, construction can begin. Install footings as level
as possible. Spread footings are used most often for tilt-up buildings, but pier footings can
be considered if conditions warrant their use. Footing locations, heights, and dimensions
should be checked and verified for correctness. Crane time is expensive if modifications
must be made while a panel is suspended over an incorrect plate or footing.




                                         Fig. 11 floor slab

       Minor mistakes in floor slab (fig.11) construction often can be masked or
corrected. A poor floor slab, however, can affect the appearance of the tilt-up panel. The
slab should be smooth and hard and construction joints should be positioned where they
will have minimum impact on panel. If the joints must fall beneath the panel, clean the
joint and fill it with caulk. Floor sealing or hardening compounds must be compatible



Dept. of Civil Engineering                   6                Govt. College of Engg., Kannur
Seminar Report 2007-08


with any chemicals or paints used on the panels or there may be problems when the
panels are stripped or painted. Proper sub-grade preparation is essential. 90% compaction
is minimum. The floor slab will only be as good as the sub-grade under it. The
construction loads (trucks, cranes etc.) require at least 5-inch slab thickness. A thumb rule
is adopted for determining the proper spacing and type of joints in the floor slab. Concrete
slump does not exceed 4-inches, this helps in controlling shrinkage problems.

       In concrete tilt wall construction, some regional areas have seen tilt wall panels
not attached to the spread footing foundation providing bearing support for the panels
themselves. In these buildings, wall panels are vertically supported on foundation pads
and shear reinforcement is provided only into the narrow pour-strip of the slab-on-grade.

Much of Section 1915.8 specifically indicates that direct foundation connection is
required for cast-in-place concrete construction. However: 1997 UBC 1915.8.3.2
exception states: “In tilt-up construction, this connection may be to an adjacent floor
slab….” Consider temporary erection loads on footing.




          TABLE 1: CONVENTIONAL FOOTINGS (UBC TABLE 18-1-C)

                             Number of Floors supported by the foundation
    Dimension
                             1                    2                   3

     Below grade             0.3048m             0.4572m             0.6096m

     Wall thickness          0.1524m             0.2032m              0.254m

     Footing thickness       0.1524m             0.1778m             0.2032m

     Footing width           0.3048m             0.381               0.4572m




Dept. of Civil Engineering                   7             Govt. College of Engg., Kannur
Seminar Report 2007-08


    I. Where design is not provided, the above Table may be used as a minimum
       foundation design for stud bearing walls, unless expansive soils are present. (UBC
       1806.3.)
   II. Width, depth and reinforcement of the footings must meet the soils report
       recommendations or design engineer's calculations if more restrictive than what is
       noted above.
  III. In seismic zone 4, continuous footings are required to have min. 1-#4 bar @ top &
       bottom.
  IV. In seismic zones 3 & 4, 1- #4 bars are required at top and bottom of footings with
       stem walls & turned-down footings with slab on-grade. (As per UBC 1806.7.1 &
       1806.7.2.)
   V. When ground slopes more than 1 unit vertical in 10 unit horizontal, stepped
       footings are required.




4.2 TILT-UP PANELS

4.2.1 FORMING TILT-UP PANELS

       The standard practice in laying out panels is to snap a chalk line on the floor slab.
Wooden, plastic, polystyrene, or metal blocks or strips can be used as forms. They should
be non-corrosive and non-staining, firmly Axed in place so they will not move during
placement. Woods are the most common material used for side forms. Often the panel
depth is designed to fit the depth of standard dimension lumber; so 0.135m and 0.184m
thick structural panels are common. The form sides can be supported and secured to the
slab by a wood or steel angle support. Any common concrete anchor can be used to attach
forms to the slab. Remember that holes in the slab left by anchorages must be repaired.

       Cant strips should be used at the juncture of the side form and slab. They reduce
concrete leakage, and give a neater appearance. A bead of caulk often is added as an
additional seal between the cant strips and the slab. The available floor area for casting
should be at least 25% greater than the area of the wall panels; otherwise the panels will
need to be cast on exterior side.




Dept. of Civil Engineering                   8             Govt. College of Engg., Kannur
Seminar Report 2007-08


       Form the door and window openings after framing the panel perimeter. Brace the
interior of the openings to prevent bowing or movement. If the opening is closer than 24
inches to a panel edge, a strong back may be needed for additional support during panel
lifting and placement.




        Fig. 12. workers place brackets to outline where the tilt-up panels outside
                 boundaries, windows and door openings will be placed.



               Apply form release agent and bond breaker to the slab and forms.
   Compatibility between bond breakers, form release agents, and paints or coatings
   used on the panels is critical. Check compatibility by consulting with the product
   suppliers. Typical thickness of wall is 0.1397m and four-hour firewalls are 0.165m
   thick.




       Fig. 13.Workers build the tilt-up panel forms out of wood connected to the
                                         braces.

       The roof structure holds the tilt-up panels in place. It acts as a diaphragm to
horizontally support the wall at the top, and the curb on the footing supports it laterally at
the bottom. The panels are generally not connected together to allow for expansion and


Dept. of Civil Engineering                    9             Govt. College of Engg., Kannur
Seminar Report 2007-08


contraction without cracking. The panels are only positively connected to the roof at their
centers near the top. Avoid „L‟ and „T‟ shaped panels because they are difficult to erect
and usually requires strong backs. Keep the ratio of height to width of solid panel
between openings to less than 4:1. For greater ratios, the code requires additional
reinforcing requirements. . When bottoms of panels must be stepped (such as for sloping
grades), the step upward should not be more than about one-third width from a panel
edge. Since panels are lifted by tilting along their lower edge, this edge should be at least
two-thirds of the panel width.

4.2.2 NUMBER OR LOCATION OF OPENINGS

       There is no limit to the number of openings, but their location can be critical.
Openings closer than the minimum from the end of the panel supporting a concentrated
roof load can add considerable reinforcing thickened concrete or steel columns. The
minimum distance is one-eight the eave height, or two feet, whichever is less. . Keep door
and window openings at least 18" from the edges of panels and a similar minimum
distance between openings. If less, there can be structural problems.

4.2.3 ANALYZING A PANEL

       It is conservative and perhaps most common to design multi-storey tilt-up panels
as simple spans between supports while accumulating axial loads from the storey above.
However the lateral wind and seismic forces transferred from the panels to the floors and
roof should be calculated using a continuous span. A simple span assumption will result
in an unconservative calculated connection force. The engineer should also make sure not
to forget to add the connection force due to thermal bowing restraint at the floor
connections.

       When designing multi-storey panels one must also consider the design of the
panel for loads during construction. Typically when a panel is on braces, the span of the
panel to the brace point is probably considerably more than the final design span. This
condition many times will control the reinforcing design of multi-storey panels.




Dept. of Civil Engineering                   10            Govt. College of Engg., Kannur
Seminar Report 2007-08


4.2.4 SEQUENCE IN WHICH CASTING A PANEL

       They should be cast with the lifting sequence in mind, so that the top panel on a
stack is the first to be placed and so that it is not necessary to lift and reset panels.
Consideration should also be given so that a panel still on the floor will not block the
setting or bracing of another. Crane reach and travel should be considered as well. The
panels should be cast so that the crane can lid them with a minimum of handling, and so
that the concrete ready-mix truck can reach them. If possible, it is desirable to cast them
with the inside face up so that the connections are visible, lifting inserts are patched to the
inside, and so the wind braces can be connected before the panels are lifted.



4.2.5 RECOMMENDED TOLERANCES FOR THE PANELS

       The American Concrete Institute Committee on Tilt-Up is writing a state-of-the-
art paper, which uses the following tolerances:


      Height and width of panel up to 9 meter - +0.00635m.
      Each additional 3 meter increment in excess of 9 meter for height or width - +
       0.003175m.
      Thickness of panels - + 0.00635m or – 0.003175m.
      Size and location of openings cast into the panel - + 0.00635m.
      Location of embedded connections - + 2.9m.
      Reinforcing steel cover – 0.00635m.




4.2.6 STACKING OF PANELS

       Basically, the lower panel is cast with a form that is two panels thick. The first
panel is cast and cured for a day, and then the reinforcing and hardware are installed in
the next panel above it. The second panel is poured and cured for a day, and then the
double thickness form is moved up one thickness to form the next panel. The form is held
to the panel for this purpose with various items, including bolt, J-hooks and J-snap-ties




Dept. of Civil Engineering                    11             Govt. College of Engg., Kannur
Seminar Report 2007-08


        Panels can be stacked as high as desired, since it is unlikely that the floor will be
overloaded. However, it will not be possible to place concrete directly from ready-mix
trucks if over about three feet high. Another consideration is the lifting techniques off of a
stack of panels.



        When the lower panel has a large opening the hole can be blocked out in wood or
filled with wet sand. A thin layer of concrete, grout or plaster is cast over it and trowel led
to match the panel surface. Bond-breaker is then applied to the surface to seal it and
prevent bonding of the concrete above it.



4.2.7 SURFACE TREATMENTS

        It is popular to impart a pattern or texture to the face of the tilt-up panels using
reveal strips. Typically these are anchored to the base slab after side forms are erected,
but before the reinforcements are placed. Concrete nails or other anchors often are used to
fasten the strips. This surface treatment must be carefully planned and executed, but the
results are striking.



4.2.8 JOINTS AND CORNERS

        Corners can be either overlapping or mitered. This must be detailed on the plans.
When overlapped, be sure one panel is shorter to allow for the overlap. Joint should be
treated for fire ratings. 2, 3 and 4 hour ratings require special sealants. Joint width should
be ½ inch up to 24 feet high and ¾ inch for taller panels. Delay welding of connections
between panels as long as possible, the longer the delay, the more shrinkage will take
place in the panels and the less chance for shrinkage cracks at the connections.




Dept. of Civil Engineering                    12             Govt. College of Engg., Kannur
Seminar Report 2007-08




                                   Fig. 14. Panel joint.

4.2.9 THICKNESS

Generally 5 ½ inch thick panels are used. Four hour firewalls are 6 ½ inch thick. . A rule
of thumb for required panel thickness is to divide the unsupported height in feet by four,
to give the required thickness in inches. For example, an unsupported height (floor slab to
roof ledges) of 22 ft. would require approximately a 5.5 inch panel, round it off to the
next higher form lumber size when available.

4.3. REINFORCEMENT

       Standard Grade 40(Fe 415) or 60(Fe 600) bars are used. The use of plastic support
chairs instead of steel chairs is recommended to avoid rust on the panel face. The correct
chair height to be used to maintain the proper depth of reinforcing.

       Minimum panel reinforcement ratio is 0.0012 for horizontal bars and 0.002 for
vertical bars (UBC-‟94 1914.3.8). Panel reinforcing should be #4 or #5 bars. Additional
sizes may be required for special conditions, but not larger than #7 for practical



Dept. of Civil Engineering                  13             Govt. College of Engg., Kannur
Seminar Report 2007-08


placements. Spacing of bars cannot exceed 18 inches, per code, and should not be closer
than about 10 inches, so workman can step between the bars. Add two #5 bars at the
bottom of panels, with hooked or 90º bends to minimize likely hood of diagonal cracks at
the lower corners of panels.




                    Fig. 15. Rebar is placed in the completed forms.




                                                                             2- #5 bars




                                                                  Where 2 feet min.
                                                                  cannot be
                                                                  obtained, extend
                                                                  as far as possible &
                                                                  bend 90 degree.

                                                                       Pad type
                                                                       footing.

                                  Floor line




                        Fig. 16.Panel Reinforcing At Openings




Dept. of Civil Engineering                     14       Govt. College of Engg., Kannur
Seminar Report 2007-08


4.4 EMBEDS AND INSERTS

        The next step is to install embeds and inserts. Embeds are pre fabricated steel
plates with lugs that are cast into the panel to attach it to the footing, other panels, or the
roof system, or for attachment of building accessories after the shell is completed. They
can be attached to the side forms if they are on the panel edges, or they can be wired to
the reinforcing.

        Inserts provide the attachment points for lifting hardware and braces. They usually
are sized by the suppliers, who also furnish engineering drawings showing insert
locations. Install inserts according to the manufacturer‟s recommendations. If there is a
field changes in panel size, opening location, or other conditions, the insert supplier
should be contacted to confirm the location and selection of hardware.




4.5 CONCRETE PLACEMENT

        Before placing the concrete for tilt-up panels, clean the base slab. Use compressed
air to blow away dirt, leaves, and other loose debris. Also remove any standing water on
the slab.




                     Fig.17. Workers pour the concrete in to the forms




Dept. of Civil Engineering                    15             Govt. College of Engg., Kannur
Seminar Report 2007-08


       Concrete placement methods for tilt-up panels are the same as those for floor
slabs. Since the panels are the structural members, make sure the concrete mix meets
specifications. Direct chute placement is the most economic method, but pumping and
bucket placement also work. Consolidate the concrete to ensure good flow around the
reinforcing steel. A trowel finish is suitable for most projects.

       As with other types of concrete construction, plan for the unexpected. If the
weather will be cold, have insulation blankets ready. If it looks like rain, delay the pour or
have a suitable covering material available. Provisions should be made to block off a pour
if a concrete truck breaks down or gets stuck in traffic. On hot or windy days, be prepared
to cure the panels by water misting or by applying a suitable curing compound.




       Fig. 18.Use of power trowels to make sure the panels are level and smooth.




           Fig.19. Panels ready for erection after curing and finishing the holes.



4.6 PANEL ERECTION

       The erection sequence should be determined well in advance, but it is a good idea
to review it immediately before panel erection. Also, thoroughly review safety procedures
with all tilt-up crewmembers to help prevent accidents. Discuss crane operation, bracing
and anchorage details, cable releases, and job communication. As soon as possible after


Dept. of Civil Engineering                    16             Govt. College of Engg., Kannur
Seminar Report 2007-08


the panels are erected dry pack or stiff grout should be placed under the panels (usually a
one-inch space) and vibrated so full bearing is achieved.

       Locate and clean inserts and embeds and attach before lifting the panels. It is
much quicker and safer to do this work while the panel is flat rather than doing it on a
ladder after the panel is upright. Don‟t remove braces until after the roof and decking are
installed. Once the braces are removed, workers can patch holes in the floor and complete
other finish work.

       Before erecting tilt-up concrete panels allow them to gain enough strength to with
stand lifting stresses. Erecting panels before achieving the proper strength may lead to
damage, costly repairs and even serious accidents. As concrete gain strength more slowly
in cold weather and quickly at higher temperature, curing time alone is not an accurate
method for determining in place concrete strength. Only reliable testing can produce
accurate estimates of in-place concrete strength. The most common testing method makes
use of field – cured cylinders.




         Fig. 20.Mobile crane erecting the panel to place it over the footing.

Dept. of Civil Engineering                  17              Govt. College of Engg., Kannur
Seminar Report 2007-08


4.6.1 SAFETY PRECAUTIONS NECESSARY BEFORE AND DURING LIFTING

       Provide the crane company with a set of panel lifting details well before the day of
lifting so that they can plan necessary rigging.

       Double-check that the rigging configuration and that the spreader bars and slings
are the correct length.

       Watch for ditches, holes and overhead obstructions that might prevent the crane
from moving.

       Have a safety meeting at the beginning of the erection to ensure that everyone
knows what is expected and how to operate safely.

       Make certain everyone on the rigging crew knows how the lifting hardware is
supposed to work.

4.6.2 BRACES

       Braces should be attached to the panels when they are still on the casting bed if at
all possible. It speeds and simplifies the erection when the braces are raised with the
panels. The braces should be removed after the roof connections and diaphragm is
completed. Braces should be disconnected from the floor first and then carefully
disconnected at the top and lowered to the ground.




Fig. 21. After placing the panel over the footing braces are connected properly to the
                                       floor slab.




Dept. of Civil Engineering                   18           Govt. College of Engg., Kannur
Seminar Report 2007-08


4.6.2.1 NUMBER OF BRACES

        Minimum two bracings are needed for aligning the panel, but large panels require
more. Check with the design charts provided with the erection design for type and
quantity of braces.

4.6.2.2 PRECAUTIONS NECESSARY WHEN BRACING TO THE FLOOR

        Be certain that the floor is of adequate thickness and strength. The inserts should
not be near edges or joints, and must be placed in large enough slab sections to withstand
uplift forces.

4.6.2.3 BRACING AND SHORING OF LINTEL PANELS

        The panel bracing and shoring should be designed by a professional engineer, and
the shores should be braced against lateral movement separately from the panel. All
members should have firm bearing on adequate foundations, and the connections should
be fixed before releasing the panel from the crane.


4.7 PANEL FINISHING

        The finish of a panel is limited only by the creativity of the architect and the
abilities of the contractor. Common sand blasted or exposed aggregate finishes can be
done immediately after panel erection. Painting, however, must wait until partial curing
has taken place and residue from the bond breaker has been removed.

        Most tilt-up concrete panels have an uneven or splotchy appearance when first
stripped. These splotches usually fade after time. Uneven bond breaker application,
standing water, slab porosity, and other factors can produce this effect. Sand blasting
most of these inconsistencies. Washing also can improve appearance, but most tilt-up
panels are eventually painted.

        Before cleaning and painting panels, caulk the joints and correct significant
imperfections. The most frequently used paints are acrylic-based. Textured paints can be
used for special effects. Building or striping is a popular technique to produce variety and
interesting tilt up buildings. Reveals or recesses cast into the panel often are painted a
contrasting or darker colour for accent.



Dept. of Civil Engineering                  19             Govt. College of Engg., Kannur
Seminar Report 2007-08


       Many tilt-up contractors are discovering that they can save time and money, in
addition to increasing the architectural options they can offer customers by applying an
exterior insulation finish systems (EIFS) to the exterior of concrete tilt-up panels.

       EIFS, sometimes called synthetic stucco, is a generic term for wall systems that
cover exterior surfaces, ranging from plywood to concrete. The expanded polystyrene is
applied to the surface with an adhesive and then is covered with a thin, polymer modified,
cementitious base coat embedding a mesh of glass fibre in the base of reinforcement. The
final step is application of an elastomeric topcoat, which is available in various colours
and textures. Tilt-up contractors can create interesting architectural projections and
decorative moulding by varying the size and shape of the expanded polystyrene. If the
goal is to simply add color and texture to the panels the elastomeric topcoat can be
applied directly to the panel surface.


4.8 INSULATING THE PANELS

       The most effective method of insulating Tilt-Up walls, however, is the method
known as "sandwich". This method is placing a layer of insulation between a structural
concrete layer and an architectural or non-structural concrete layer during the casting of
the panel and then tilting this entire construction as a panel. This method is made possible
by structurally connecting the two concrete layers through the insulation layer. As soon as
the panel is erected to final position, the inside layer becomes structural and load bearing,
while the outer concrete layer is suspended from it to allow for temperature changes
without cracking. It is critical that these two layers remain independent from each other
except for the connection through the insulation. The basic forming and pouring process
must be modified slightly to accommodate the sandwich wall system. Higher side forms
are needed to accommodate the insulation, and some systems require concrete placement
on separate days. Tilt-up sandwich panels with as much as 6 inches of insulation and R-
values of 30 can be built




Dept. of Civil Engineering                   20             Govt. College of Engg., Kannur
Seminar Report 2007-08


5. FIRE RESISTANCE OF TILT UP PANEL.
        The fire resistance of Tilt-Up walls is easily referenced or calculated in the current
UBC and IBC codes. Fire resistance is related to an R rating that determines time duration
based on the thickness and type of material.

    The following table is reprinted from the data contained in both the UBC and IBC
codes. It shows the relative thickness required for each aggregate type to meet the listed
fire resistivity rating.



      TABLE 2 Fire Resistance of Single-Layer Concrete Walls (UBC/IBC Tables)

                           1 hour    11/2 hour        2 hour         3 hour     4 hour

 Aggregate type

                                      Minimum equivalent thickness (meters)

 Siliceous             0.09         0.1092        0.127             0.16       0.1778

 Carbonate             0.08         0.1016        0.117             0.14       0.1676




                                    Fig. 22. Steel joist to wall.




Dept. of Civil Engineering                       21             Govt. College of Engg., Kannur
Seminar Report 2007-08


6. ADVANTAGES OF TILT –UP CONSTRUCTION

       The construction market is highly competitive, and tilt-up is chosen only when its
advantages, given the local and circumstances of a project, clearly favor it. And not every
building is suitable for tilt-up. To effectively and economically use tilt-up, some basic
criteria should be met. The building should be at least 5,000 square feet (the larger the
more economical), to allow enough room to cast panels and effective use of crane and
rigging crew. There should be extensive wall surface, such that it can be divided into lift
able panels and there should not be over about fifty percent openings in the panels. While
one- and two-storey buildings are most economical, many construct three- and four-
storeys high.

When these basic conditions are met, tilt-up offers numerous advantages:

       1. ECONOMY:-In areas where tilt-up design and construction expertise is
           available- particularly a trained crane and rigging crew tilt-up has proven to be
           more economical than competing construction methods for similar types of
           buildings. Tilt-up concrete is an economically viable method for building
           individually designed reinforced concrete structures. The process requires few
           forms and makes efficient use of modern mechanical equipment. RMC for tilt-
           up is locally available and special labour skills are not required. Panels are
           formed and cast on the jobsite, and can be quickly tilted, lifted, set in place,
           and braced with the aid of high capacity mobile cranes.

       2. SPEED OF CONSTRUCTION: - From the time the floor slab is placed, the
           typical elapsed time from starting to form the panels until the building shell is
           completed is 4–5 weeks.

       3. DURABILITY: -Materials and methods of tilt-up construction ensure
           durability. Early tilt-up construction, erected in the 1940's, remains in good
           condition today. The use of plastic support chairs instead of steel chairs is
           recommended to avoid rusting.

       4. FIRE RESISTANCE: - Concrete is an obvious first choice for fire resistance.
           A 0.165 m thick wall, for example, has a four-hour fire resistive rating.




Dept. of Civil Engineering                  22             Govt. College of Engg., Kannur
Seminar Report 2007-08


        5. LOW MAINTANANCE COSTS: - Building                        maintenance requirements
              are limited to a new coat of paint every six to eight years.

        6. LOWER OPERATING COSTS: - There are a number of ways to form
             individual panels.

        7. EXPANDABILITY: - By planning for the possibility of expansion, panel
             connections can be designed so the panels can be detached and relocated.

        8. SECURITY: -Panel thickness and strength make them virtually impenetrable.
             Forced entry can only occur through door and window openings.
        9. LOW HEATING/COOLING COSTS: - The insulation value for tilt-up
             concrete often exceeds masonry and wood frame construction. Tilt-up walls
             can be economically insulated to give higher insulation values.
        10. ARCHITECTURAL AESTHETICS: - Patterns or texture can easily be added
             to the face of Tilt-Up panels.
        11. LOWER INSURANCE RATES: - The fire resistance of tilt-up concrete walls
             results in lower premiums.

DISADVANTAGES

            1. Lack of design flexibility.
            2. Not a factory controlled production to assure quality.
            3. It is a weather dependent construction.
            4. For erecting highly equipped machines are needed.


7. INTEGRALLY COLOURED TILT -UP
CONCRETE
             While most tilt-up buildings are still finished with paint or other coatings, the
wave of innovation in the industry has introduced integrally colored concrete as an
alternative for high-quality tilt-up projects.

Integrally colored tilt-ups can benefit concrete producers in three ways

            Colored tilt-ups help increase the overall use of concrete in a community




Dept. of Civil Engineering                       23           Govt. College of Engg., Kannur
Seminar Report 2007-08


           By strategically promoting colored concrete tilt-up and developing a
            reputation for product quality, a ready-mix company can position itself to
            become the preferred supplier to tilt-up contractors in its community
           Many ready-mix producers report more profit from value-added services like
            colors than from the concrete itself


8. STEEL AND TILT –UP TOGETHER: USING THE
STRENGTHS OF EACH
        A large steel office building or retail center may use tilt-up concrete panels for
interior fire walls or exterior facades. The Mervyn's department store in the Dallas / Fort
Worth, Texas area (fig .25) was constructed in just this manner.




                   Fig. 24. Mervyn's building in the Dallas / Ft. Worth




9. PRECAST AND TILT -UP CONCRETE
            Over the last decade joint precast and tilt-up parking garage construction is
probably the best-known combined application of the two systems. Concrete cast in the
position it is to occupy in the finished structure is called cast in place concrete. Concrete
cast and cured elsewhere is called precast concrete. Tilt-up concrete is a special type of
precast concrete in which the units are tilted up and placed using cranes or other types of
lifting devices.




Dept. of Civil Engineering                   24            Govt. College of Engg., Kannur
Seminar Report 2007-08


10. SITE CONDITIONS THAT LIMIT TILT-
UPCONSTRUCTION

      Access by the crane to the job site.
      Relatively flat terrain to allow the crane operation.
      Any power lines, ditches, railroad tracks, or other obstructions, which limit crane
       operation.
      Other buildings very close to where panels must be placed.




Dept. of Civil Engineering                    25               Govt. College of Engg., Kannur
Seminar Report 2007-08



11. CONCLUSIONS

      Tilt-up construction is a fast growing construction method. In comparison to other
modes of construction, it is economically and practically viable and advantageous. The
advantage that it can claim is manifold, and in comparison, its drawbacks are mere and
insignificant. The tilt–up construction technique is widely used and accepted in developed
nations such as America. Owing to its versatility, it can be said with confidence that this
technique can be applied to its full potential even in developing nations such as India.




Dept. of Civil Engineering                   26            Govt. College of Engg., Kannur
Seminar Report 2007-08


REFERENCES

         1. ACI 551-92, „Tilt-Up Concrete Structures’, American concrete institute,
            Detriot.

         2. Brooks.H.E, „The Tilt-Up Design and Construction Manual’, second edition,
            1990, H.B.A publications, Newport Beach.

         3. Edward sauter.J, ‘Special Formwork for Tilt-Up’, Concrete international,
            October 2002.

         4. Edward sauter.J, „Today’s Tilt-Up – Commingling Structural Design and
            Greater Aesthetics ’, Concrete international, April 2002.

         5. James. R. Batty, ‘A Convenient Marriage: Tilt-Up And Precast’, Concrete
            international, May 2004.

         6. Nick Paris and Michael Chusid, „Integrally Coloured Tilt-Up Concrete’,
            Concrete international, August 2000.




Dept. of Civil Engineering                 27            Govt. College of Engg., Kannur

				
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