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Tilt-Up Construction...

Build with tilt-up, the most advanced construction method for:

• warehouse facilities
• distribution centers
• office complexes
• shopping centers
• industrial buildings
• low-rise commercial
• waste water tanks
• low to mid-rise structures
• schools
• prisons
• motels
• homes

When you construct a new building, regardless of its purpose, you want a building that works, is attractive, reasonably priced, and efficient - a building in which you can take pride! You can have all of these benefits with tilt-up concrete construction.

Tilt-up concrete construction is not new; it has been in use since the turn of the century. Since the mid-1940s it has developed into the preferred method of construction for many types of buildings and structures. Nationwide, over 15% of all industrial buildings are tilt-up, ranging in size from 5,000 to over 1.5 million square feet. They are typified by their attractiveness, efficiency and longevity.

Design-build - the fast delivery system for your project where the building construction proceeds while the design is being developed, speeding completion. Tilt-up lends itself to this process because construction of the wall panels can proceed whle the rest of the building is being designed.

You'll get earlier occupancy - when you decide to build, you want to proceed quickly. With tilt-up, you get compression of disciplines - many phases proceed simultaneously. Therefore, you can move into your building sooner.

Assembly line prefabrication - load-bearing reinforced concrete wall panels are cast horizontally on the floor slab or a casting slab, and are tilted up into their final vertical position with high-capacity mobile cranes. The entire process is designed for efficiency and speed of erection.

Trades get in sooner - because the floor slab is poured first, the other trades can work sooner, and have a better work environment. That saves both time and money.

Materials and labor are more readily available - site-cast tilt-up uses ready mixed concrete usually available near the job site. Contractors use local labor.

In-place material costs are more competitive than precast, masonry and steel structures; fewer skilled laborers are needed to achieve high-quality construction. In addition, the speed of erection and the ease of other subcontractors' work, further reduces costs.

Costs are easier to control because there are fewer variables with tilt-up. Ready mixed concrete, made from readily available native materials, has price stability. Vertical forming and scaffolding are eliminated; less skilled labor is needed; and, the short construction cycle precludes cost run ups. Weather is less of a problem, since the floor slab provides a stable work surface for the trades.

Positive cash flow - materials are used as soon as purchased, allowing for early payment, unlike off-site fabricated building components requiring long lead times.

Less heat and air-conditioning will be required for your tilt-up building; and, smaller, less costly mechanical systems can often be used. The thermal mass inherent in concrete reduces the heating and cooling peaks and loads. Insulation systems are available that enable the construction of integral sandwich walls or lightweight interior insulation. The national Energy Policy Act of 1992 mandates improved energy performance in commercial buildings, and recognizes the effect thermal mass contributes to reducing heating and cooling loads.

You'll have lower insurance premiums because:

• concrete provides more fire resistance than comparable steel buildings or wood-frame structures;
  
• tilt-up concrete structures have been shown to withstand wind storms and earthquakes better than comparable buildings of other materials; and
  
• security is better with solid concrete walls.

Maintenance - Your new tilt-up concrete building will require less maintenance. The exterior can be left unpainted with no damage from the elements. If painting is desired, it need be repainted only every five to ten years. Concrete interiors are less subject to damage, and easier to wash down.

Expansion. Your tilt-up concrete building can be designed and built to allow easy expansion, simply by detaching and relocating the concrete panels or cutting new openings.

Sound Control. If you are in a noisy area, such as near an airport, you will enjoy the added benefit of the sound reduction properties of concrete. The mass absorbs the sound rather than letting it through as in metal and wood-frame buildings.

Safety. Most work is on the ground - there is no vertical formwork, no scaffolding, since walls are constructed horizontally. In addition, since the floor slab is poured first, workers have a safer working surface.

Labor crews are smaller - without vertical forming, or other costly erection processes, few workers are needed, especially during the lifting operation. The short project cycle presents less opportunity for accidents.

Architectural Aesthetics

Any tilt-up structure can be an attractive building in which you can take pride. The large tilt-up panels lend themselves to a variety of decorative treatments:

• An unlimited array of colorings that can be added to the concrete mix or textured paints of any color may be used for beautiful effects.
• Textures produced with improvised techniques and form-liner cast surfaces in a variety of patterns, including striated, fractured fin, stone, brick and woodgrains.
• Exposed aggregate and mechanical tooling surface treatments.
• Trompe l'oeil painting and simple forming on the casting surface can produce the effect of three-dimensional surfaces.

Durability

The strength of tilt-up concrete buildings was proven in the Northridge, California earthquake, where tilt-up walls stood, even when roof connectors failed. What's more, buildings constructed in the 1940s show little sign of age after 50 years. In fact, buildings dating back to as early as 1906 are still in service today. Tilt-up structures withstand wind and hail storms and are impenetrable by the smallest rodent, insect, or even the most determined human.

Of minimal concern is localized damage to a concrete building from a truck or fork-lift. Metal or wood buildings will usually sustain substantial damage from similar incidents.

Fire resistance of concrete can extend the building's life, plus tilt-up panels may be used for the interior fire walls, and buildings may be spaced closer together under many building codes.

Tilt-Up Construction Guidelines...

Tilt-up construction is one of the fastest growing industries in the United States. At least 4,000 buildings enclosing 160 million square feet are constructed annually. This is due, in part, to the economics of tilt-up, which combine reasonable cost with low maintenance, durability, speed of construction, and minimal capital investment. These advantages are most evident in buildings greater than 10,000 square feet with 20-foot or higher side walls and repetition in panel size and appearance.

A successful tilt-up project begins long before concrete is poured. As with any project, the key is thorough planning. An experienced tilt-up contractor can be successful on a wide variety of projects. The beginner, however, should choose more carefully. This article explains the basic methods and skills required for successful tilt-up construction.

Site evaluation. Planning begins with an evaluation of the site. A large, flat, open site is ideal, but not common. Therefore, evaluate the site with regard to slab layout and the movement of materials and equipment around the slab. If the site is tight around the building, consider sequencing the pouring of slabs and panels from within the building. A plan or sketch showing the pouring and erection sequence relative to the site and floor plan of the building can identify potential problems.

Engineering. Engineering is a critical phase of tilt-up projects. Consult an engineer with experience or familiarity with tilt-up construction and current design methods. Current recommendations for many aspects of tilt-up, particularly engineering, are presented in ACI 551R (Ref. 1).

Engineering tilt-up panels to withstand service and lifting loads is critical. But using a design that is too conservative could produce panels that are thicker and heavier than required. The net result could be larger footings, bigger cranes, more panels, and more joints - all of which can increase the cost of the project to the point where it is not cost-competitive.

The thickness of a concrete panel usually is determined by a quantity called the slenderness ratio. This is the ratio of the unsupported panel height (usually the distance between the floor slab and the roof structure attachment) to the panel thickness. The generally accepted slenderness ratio on tilt-up walls is 50. However, a qualified engineer should make the final determination.

Floor slabs must be designed to support crane loads during erection. These loads may exceed building occupancy loads in some cases, so select the crane early in the project. Most contractors use at least a 5- or 6-inch-thick slab, unless structural requirements dictate a thicker one.

Panel connections to the footings, floor system, roof, and between panels also are details designed by an engineer, and must be determined before construction.

The loads applied during lifting generally have the greatest affect on the panels. Locations of openings, lifting inserts, and other parameters must be considered. Additional reinforcement usually is needed to accommodate these loads. Tilt-up accessory suppliers can be helpful in this aspect of design. Most will provide panel layouts indicating locations of lifting inserts and other information critical for erecting the panel.

A product of the design phase should be a drawing of each panel, preferably showing both the front and back, and insert and embed locations. The contractor or engineer should produce a building floor plan showing the layout of every panel on the slab and the erection sequence.

Several other items must be considered during the planning and engineering phases of the project. These include surface treatment, anticipated weather conditions, and material and equipment availability. For example, if the panels are to have deep reveals, a thicker panel might be required since the cross section of the panel could be reduced at a critical point by the reveal.

Careful consideration should be given to the size, location, and attachment of temporary wall braces. Here, again, tilt-up accessory suppliers can be helpful. Experienced tilt-up engineers also can offer economical bracing schedules.

Footings and floor slabs. Once planning is complete, construction can begin. Install footings as level as possible, with attachment plates (if used) placed properly. 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. Setting a panel down after it has been lifted interrupts the construction schedule. Also, panel lifting hardware may be designed for only one pick, so repeated handling can reduce the safety factor for that hardware.

Minor mistakes in floor slab 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 contraction joints should be positioned where they will have minimal impact on the panel. If the joint must fall beneath the panel, clean the joint and fill it with caulk. Floor sealing or hardening compounds must be compatible with any chemicals or paints used on the panels or there may be problems when the panels are stripped or painted.

Forming tilt-up panels. The standard practice in laying out panels is to snap a chalk line on the floor slab. These lines indicate panel perimeters and the forms should be placed against them. Wood 2xs are the most common material used for side forms. Often the panel depth is designed to fit the depth of standard dimension lumber, so 5 1/2- and 7 1/4-inch-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.

There are several ways to form individual panels. One way is to form the perimeter of a series of panels, then use 1x or 2x strips to divide the area into panels. Advantages of this method include less forming and reduced forming lumber costs. Close joint tolerances from panel to panel can be maintained since adjacent panels share a form.

A variation of this method is to cast a large slab, then saw joints into the slab to form individual panels after the concrete has been troweled.

Use cant strips at the juncture of the side form and slab. They reduce spalling when stripping forms, help close off the bottom of the form to reduce concrete leakage, and give a neater appearance. A bead of caulk often is added as an additional seal between cant and reveal strips and the slab.

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

Apply form release agent and bond breaker to the slab and forms as recommended by the manufacturer. A wide variety of materials are available. 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.

Surface treatments. It is popular to impart a pattern or texture to the face of tilt-up panels using reveal strips. Typically, these strips are anchored to the base slab after side forms are erected, but before reinforcement is 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. A reveal strip that is 1 inch off is difficult to correct once the panel is erected. Other finishes include exposed aggregate, sandblasted, and brick or stone facings.

Reinforcing. The steel grid for reinforcing tilt-up panels is typically tied in-place after the side forms are erected. Standard Grade 40 or 60 bars are used. The use of plastic support chairs instead of steel chairs is recommended to avoid rust on the panel face. If steel chairs must be used, use a type that is plastic-tipped. Check to make sure the tips are in place just before the pour. If insulated panels are used or the pour is on a sand bed, use chairs with sand feet. The weight of the steel can force a standard chair foot into the sand or insulation. Use the correct chair height to maintain the proper depth of the reinforcing.

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 supplier, who also should furnish engineering drawings showing insert locations. Install inserts according to the manufacturer's recommendations. If there is a field change in panel size, opening location, or other conditions, the insert supplier should be contacted to confirm the location and selection of hardware.

Concrete placement. Before placing 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.

Concrete placement methods for tilt-up panels are the same as those for floor slabs. Since the panels are structural members, make sure the concrete mix meets specifications. Direct chute placement is the most economical 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.

Panel erection. The erection sequence should be determined well in advance, but it's a good idea to review it immediately before panel erection. Also, thoroughly review safety procedures with all tilt-up crew members to help prevent accidents. Discuss crane operation, bracing and anchorage details, cable releases, and job communication.

Locate and clean inserts and embeds and attach braces 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 braces are removed, workers can patch holes in the floor and complete other finish work.

Panel finishing. The finish of a panel is limited only by the creativity of the architect and the abilities of the contractor. Common sandblasted 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. Sandblasting eliminates most of these inconsistencies. Washing also can improve appearance, but most tilt-up panels are eventually painted.

Before cleaning and painting panels, caulk joints and correct significant imperfections. The most frequently used paints are acrylic-based. Textured paints can be used for special effects. Banding or striping is a popular technique to produce variety and interest in tilt-up buildings. Reveals or recesses cast into the panel often are painted a contrasting or darker color for accent. The trompe l'oeil, or "fool-the-eye," effect is quite striking and popular.

Insulated panels. Insulated tilt-up panels are a rapidly growing market providing new opportunities to experienced and new tilt-up contractors. Several proprietary systems enable contractors to insulate panels during their construction or after the building is erected. The basic forming and pouring process must be modified slightly to accommodate the sandwich wall systems. 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. Usual applications include coolers and freezers.

Tilt-Up FAQ