Tilt Up Construction

SEMINAR REPORT ON

TILT – UP CONSTRUCTION

BY

ARJUNA.S. (4AI06CV003)

TILT – UP CONSTRUCTION

CONTENTS

INTRODUCTION

CONSTRUCTION

ADVANTAGES

What is Tilt-up Construction? How Are Tilt-up Concrete Buildings Constructed?

A tilt-up construction project begins with job site preparation and pouring the slab. During this phase of the project, workers install footings around the slab in preparation for the panels. The crew then assembles the panel forms on the slab. Normally, the form is created with wooden pieces that are joined together. The forms act like a mold for the cement panels. They provide the panels' exact shape and size, doorways and window openings, and ensure the panels meet the design specifications and fit together properly. Next, workers tie in the steel grid of reinforcing bars into the form. They install inserts and embeds for lifting the panels and attaching them to the footing, the roof system, and to each other.

The slab beneath the forms is then cleaned of any debris or standing water, and workers pour concrete into the forms to create the panels.

Now comes the point where tilt-up construction, or tilt-up construction, gets its name.

Once the concrete panels have solidified and the forms have been removed, the crew connects the first panel to a large crane with cables that hook into the inserts. The size of the crane depends on the height and weight of the cement panels, but it is typically two to three times the size of the largest panel. The crew also attaches braces to the tilt-up panel. The crane lifts, or "tilts up," the panel from the slab into a vertical position above the footings. Workers help to guide the concrete panel into position and the crane sets it into place. They connect the braces from the tilt-up panel to the slab, attach the panel's embeds to the footing, and disconnect the cables from the crane. The crew then moves to the next panel and repeats this process.

It's easy to be amazed as you watch the mobile crane tilt up a concrete panel from the ground and set it into its place. Massive cement panels weighing 50,000 to 125,000 pounds or more dangle from the crane's long lines. The crew works as a team, setting the braces and guiding the tilt-up panel with remarkable precision. The

speed of the process is also remarkable; an experienced tilt-up crew can erect as many as 30 panels in a single day.

Once all the tilt-up construction panels are erected, the crew apply finishes to the walls with sandblasting or painting. They also caulk joints and patch any imperfections in the walls. From this point the crew moves to the installation of the roof system and the trades begin their work inside the building.

Why do Design Build Contractors Choose Tilt-up Construction?

Tilt-up construction provides numerous advantages over steel buildings or traditional construction for warehouses, call centers, distribution centers, retail stores, office buildings, storage facilities and other types of industrial and commercial building construction projects. Generally speaking, a one- to two-story structure larger than 50,000 square feet with less than 50% wall opening space is an excellent candidate for tilt-up concrete construction.

But what are the advantages?

Savings in Construction Costs - Tilt-up construction provides numerous construction cost savings. This method of concrete construction uses locally available materials rather than ones that must be manufactured and shipped in. This means that raw material costs are lower, available when needed and less prone to price fluctuations. Tilt-up work crews are typically smaller than the crews used in traditional construction and are normally comprised of local labor. That translates to reduced labor costs. Because of the economies of scale, the larger the footprint for the building, the more these savings improve the project's total cost.

Fast Construction Schedule - Tilt-up construction offers several opportunities to "compress" the schedule and deliver the building very quickly. Erecting the walls with tilt-up panels is faster than building walls using traditional construction

techniques. The trades can begin work earlier in the process on a tilt-up project, which allows greater overlapping of project phases. Because the building is made of ready-mix concrete from local sources, the project is less likely to be affected by transportation delays as well. All these factors provide for a faster, more predictable schedule with fewer opportunities for delays and associated cost overruns.

Safety - Tilt-up concrete is a proven, safe method of construction. The vast majority of the project takes place on the ground rather than on scaffolding, reducing many of these risks normally faced by workers.

Aesthetics - Tilt-up concrete buildings are not prefabricated. Each one is custom-designed for the client's needs and preferences. A full range of building finishes, wall textures and adornments, colors, even curved walls, are available with this method. Tilt-up construction provides architects and designers with virtually unlimited flexibility in crafting a building that is functional, durable and aesthetically pleasing.

The benefits of a project built with tilt-up construction continue long after it is completed:

Durability - Tilt-up concrete buildings are extremely durable. Many structures created in the 1940s are still in operation today, with little apparent wear. A testament to the strength of tilt-up construction, general contractors in earthquake-prone California now use this method for 90% of their one-story industrial building projects.

Fire Safety - The concrete used in tilt-up panels meets the fire-resistance standards of even the most demanding building codes. For example, a 6.5" concrete wall offers a fire resistance rating of four hours or more. Tilt-up panels are also frequently used in the building's interior as fire walls. Tilt-up buildings offer real protection and safety for their tenants' employees, property and ongoing operations.

Ease of Maintenance - Tilt-up construction buildings require little in the way of ongoing maintenance, outside of periodic cleaning and repainting as desired. Concrete is impervious to insect or rodent infestation, so this problem becomes a relative non-issue as well.

Reduced Insurance Premiums - Because tilt-up concrete buildings have superior fire resistance ratings and have been proven to withstand severe weather and earthquakes, these cement buildings typically enjoy better insurance rates than steel buildings or other types of structures.

Reduced Operating Costs - Concrete provides excellent insulation, reducing the ongoing heating and cooling costs for the tenant. This insulation extends to sound as well as temperature. Workers in a tilt-up office building located in a noisy area will be less affected by the environment. By the same token, a manufacturing business that generates noise will have less effect on its neighbors and will find it easier to comply with local noise ordinances.

With a better understanding of these benefits, it's easy to see why many design / build contractors, construction managers and savvy building owners are opting for tilt-up over steel buildings or traditional construction for commercial building construction projects. Delivering value, speed and responsiveness, quality, durability, reduced construction costs, and ongoing cost savings in operating expenses, tilt-up construction is the best choice for a wide range of commercial construction projects.

Steel Buildings and Tilt-up Concrete Construction Together: Using the Strengths of Each

An important fact to remember is that the use of steel in building is not necessarily exclusive of concrete or blocks. In larger or more sophisticated projects the

different raw materials and construction methods are frequently used together.

Here are some very common examples of how steel, concrete and tilt-up construction are used together to provide the best quality and value:

A large steel office building or retail center may use tilt-up concrete panels for interior fire walls or exterior facades. The Mervyn's retail store in Dallas / Fort Worth, Texas pictured to the right was constructed in just this manner.

An existing manufacturing building or warehouse made of concrete blocks could be expanded by adding a steel lean-to structure to one of its exterior support walls.

A distribution center built using the cement blocks of traditional construction will frequently use a steel roofing system and a rigid frame similar to what a metal building might use. Regardless what material is used, this combination of a rigid frame and steel roof is necessary to provide a large clearspan.

These are just a few situations where the best choice for a project might be a steel building with tilt-up construction components, or a concrete structure with steel framework, roof system or steel add-ons or expansions. A general contractor who is well versed in the advantages and limitations of all methods of construction can help determine what is the best approach on any given project. Visit our Construction Links page for general contractors and construction managers who are experienced in tilt-up construction

Precast Concrete, Tilt-up Construction and Tilt wall: What's the Difference in These Terms?

Several terms - tilt-up panel construction, tiltwall construction, precast concrete building construction - are used to reference new or nontraditional cement building processes. Do they all mean the same thing? If not, what are the differences?

As previously stated in this article, tilt-up and tiltwall are two terms used to describe the same process. For a tilt-up concrete building, the walls are created by assembling forms and pouring large slabs of cement called panels directly at the job site. The cement panels are then tilted up into position around the building's slab to form the walls. Because the concrete tiltwall forms are assembled and poured directly at the job site, no transportation of panels is required. One major benefit of this is that the size of the panels is limited only by the needs of the building and the strength of the concrete panels themselves.

Tilt-up construction panels can sometimes be extremely wide and/or tall. Tilt-up concrete panels have been measured at just over 69 feet across and almost 93 feet from top to bottom. Thus, architects and tilt-up concrete contractors have a great deal of flexibility in planning and creating their buildings.

Because concrete tilt-up walls are poured outdoors, contractors are at the mercy of climatic conditions. When temperatures drop below freezing, curing the concrete panels becomes more difficult and expensive. This is why tilt-up concrete construction is particularly popular in southern parts of the United States, where cold weather occurs less frequently. Certainly, tilt-up concrete buildings are built in northern areas, but the window of time for temperate weather is much smaller and less predictable, which can make construction schedules more difficult to meet.

The precast concrete building process is similar to tilt-up construction, but it addresses the challenges presented by weather. For precast concrete buildings, work crews do not set up forms at the job site to create the panels. Instead, workers pre cast concrete panels at a large manufacturing facility. Because the precast concrete forms are poured indoors, this activity can take place regardless the weather conditions. After curing, the precast concrete panels are trucked to the job site. From this point, precast concrete buildings are assembled in much the same manner as tiltwall buildings.

The fact that precast concrete walls are formed at a manufacturing facility resolves the weather issue, but presents a different limitation

not found in tilt-up construction. Because the panels must be transported - sometimes over long distances - places a substantial limitation on how wide or tall each panel can be. It would be impossible to load precast panels that were 60 feet wide or 90 feet long onto trucks and transport them any distance. For a precast construction project, the panels must be smaller and more manageable to allow trucks to haul them over the road to their final destination. This places greater design restrictions on architects and limits the applications where precast construction can be used.

Clearly, tilt-up concrete construction and precast concrete are similar processes. Because tilt-up affords more flexibility, it is the method of choice in locations where the weather allows it. Precast concrete is a suitable choice in circumstances where environmental factors and the construction schedule preclude tilt-up as a viable option.

When Does Concrete and Tilt-up Construction Make More Sense Than Steel Buildings?

There are several factors that may make other methods of construction, most notably tilt-up construction, a better choice than steel buildings.

The most obvious factor is the building's size. For projects less than 50,000 square feet, steel is generally the least expensive alternative. For a building of this size, the fixed or "open the door" costs of a tilt-up construction project (like the rental of a large crane, for example) make it more expensive than steel, even though concrete is usually a less expensive raw material. As projects become larger than 50,000 square feet, however, the lower price of concrete starts to offset tilt-up construction's fixed costs and this method becomes cost-competitive with a metal building. The larger the building, the more advantageous tilt-up construction becomes.

The cost of the steel building kit will usually be lower than a price quoted for a concrete building, even a tilt-up construction building. If customizing or modifications to the kit are necessary to meet the owner's needs, these design costs must be included when comparing the prices. Also, the kit price may not include costs that are normally incorporated into a quote for a tilt-up or traditionally constructed

building. Some of those costs include concrete foundation, permits, erection and assembly costs, taxes, electrical wiring, plumbing, environmental controls, ductwork, interior finishing, etc.

The location of the project will also influence whether a steel building is even an option. Builders in agricultural or lightly populated areas generally have fewer code restrictions placed on them. The closer a building is planned to a densely populated area, the more stringent the fire codes, building permitting requirements and other municipal standards become. In some cases steel buildings can not be used in certain areas for this reason. Other times, fire codes may require steel buildings to be built further apart than tilt-up concrete structures, requiring a larger plot of land for the project. This is why, in urban areas, buildings closer to the downtown area are generally made of concrete and steel buildings become more common on the outskirts of town.

The reason steel buildings face greater code limitations is that they generally offer less fire protection than tilt-up or other concrete buildings. While steel is not combustible, it is not considered fireproof because it can distort or lose its structural strength when exposed to heat. Further, a fire on one side of a metal wall can generate destructive heat on the other side, damaging the property inside. Steel building designers use a variety of technologies, from sprays to fire-retardant panels or blankets, to mitigate the fire-resistive problem. By comparison, a typical 6.5" concrete wall has a fire resistive rating of four hours or more. Tilt-up and concrete provide superior fire protection for the property and people inside a building.

The intended use for a building will also influence whether steel or concrete is the best choice. In general steel buildings work very well for storage buildings, indoor sports facilities, work shops, and aircraft hangers, but they are less suited for higher-trafficked buildings. Comparatively speaking, steel walls are less durable than concrete walls. This holds true in the face of natural forces (bad weather, earthquakes) as well as for truck or forklift accidents. When a building is damaged by a vehicle, the damage is generally more localized and less expensive to repair for a tilt-up or concrete building than for a steel building. For owners who want to build a warehouse or other facility where trucks or forklifts will be used, this can be a very

important consideration. Defense contractor facilities, prisons, or other buildings that require positive security also are much better suited to impenetrable concrete than to comparatively insecure steel.

While steel is reasonably durable, concrete remains the material of choice for buildings that require less upkeep and maintenance over the years. Concrete is impervious to corrosion, rotting, rust or insect infestation; tilt-up concrete buildings created in the 1940s are still standing today with little apparent wear. The fact that builders in earthquake-prone California now use tilt-up construction for 90% of their single-story commercial projects indicates that concrete buildings are cost-competitive and extremely durable.

When factoring in potential repairs and ongoing maintenance, it's apparent that the real dollar difference between operating a steel building and a concrete building can be significant. Further, the added fire safety and durability of a concrete building will usually be reflected in lower insurance premiums. If the owner decides to sell the property, they will most likely find that a tilt-up or other concrete building depreciates less and than a steel building will.

Innovations in Tilt-up Construction Help Contractors Overcome Challenges

The key to successful commercial construction is balancing quality with cost and schedule. While this is always a challenge, external forces like local building codes often make the balance even more difficult to achieve.

Such was the case with Northern Tool & Equipment Company's retail store in Lewisville, Texas.

The construction team, headed up by general contractor Bob Moore Construction in Arlington, Texas, decided this would be a tilt-up concrete building very early in the design process. Tilt-up provided substantial cost savings and made the proposed building schedule much more feasible than traditional a CMA concrete building would allow for. Steel buildings were competitive in cost and schedule to tilt-up, but local zoning did not allow for metal structures in this location and the client wanted the superior quality of a concrete building. Tilt-up was clearly the construction method of choice.

When the decision was made, however, another issue arose. Local building codes required new commercial buildings to have 100% masonry façades. "We built a Northern Tool and Equipment retail store the year before in Grand Prairie," said Curt Hellen, Senior Project Manager for Bob Moore Construction, "and we finished that with paint. We couldn't do this in Lewisville, however, because local codes required a masonry finish to the building."

The construction team decided the Northern Tool & Equipment store would be a tilt-up concrete building very early in the design

process because tilt-up provided substantial cost savings and made the proposed

building schedule much more feasible. When the decision was made, however, another

issue arose. Local building codes required new commercial buildings to have 100%

masonry facades. The solution was a product called Brick Snap. This product

allowed construction crews to attach a brick wall facade to the tilt-up construction panels

as the panels were cast rather than constructing a façade in a separate step after

the walls were cast and stood.

In previous years the alternative would have been to build a masonry façade along the walls' exteriors. This would have driven up construction costs and added crucial days to the schedule, all but erasing the benefits of tilt-up construction.

"We had to come up with a more innovative solution," said Hellen.

The solution was found in a product from Scott System called Brick Snap. This product allowed construction crews to attach a brick wall façade to the tilt-up construction panels as the panels were cast rather than constructing a façade in a separate step after the walls were cast and stood.

To use the Brick Snap system, workers placed individual masonry tiles connected by plastic trays into the tilt-up construction panel forms. The tiles, coated in wax to ensure their faces didn't stick to the concrete, form the walls' bricks while the trays define the mortar pattern between the bricks.

Once the work crews set up the tiles and trays, they poured the tilt-up panels and allowed them to cure, then stood and secured the panels to form the walls. Workers then washed the walls' exteriors with warm water to remove the trays and wax and leave the masonry tiles in the finished brick pattern.

To use the Brick Snap system, workers placed individual masonry tiles

connected by plastic trays into the tilt-up construction panel forms. The tiles,

coated in wax to ensure their faces didn't stick to the concrete, form the

walls' bricks while the trays define the mortar pattern between the bricks.

Once the work crews set up the tiles and trays, they poured the tilt-up

panels and allowed them to cure, then stood and secured the panels to form the walls. Workers then washed the walls' exteriors with warm water to

remove the trays and wax and leave the masonry tiles in the finished brick

pattern.

The Brick Snap system worked - the project satisfied the city's requirements while maintaining the cost and speed advantages that tilt-up construction provides. "Our team took a very innovative approach to solving the various challenges we faced in the design and planning phases," said Hellen. "The steps we took were very effective, and were successful at holding down the overall cost of the project."

The Brick Snap system is another example of how the construction industry is driving innovations to manage costs and schedule without undercutting quality - the key benefits of tilt-up concrete construction. As these creative solutions are improved and implemented, tilt-up construction will continue to evolve into the construction methodology of choice for an ever-growing circle of commercial building applications.

Tilt-Up Basics: Concrete Review the basic methods and skills of modern Tilt-Up

construction

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.

Tilt-Up Basics: Embeds and Inserts

Review the basic methods and skills of modern Tilt-Up construction

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.

Tilt-Up Basics: Engineering Review the basic methods and skills of modern Tilt-Up

construction 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.

Tilt-Up Basics: Footings/Floor Slabs Review the basic methods and skills of modern Tilt-Up

construction 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

Tilt-Up Basics: Insulation


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 Basics: 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.

Tilt-Up Basics: Panel Forming

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 2x's are the most common material used for side forms. Often the panel depth is designed to fit the depth of standard dimension lumber, so 5½- and 7¼-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.

Basics: Planning and 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.

Tilt-Up Basics: 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.

Tilt-Up Basics Review the basic methods and skills of modern Tilt-Up

construction

Tilt-Up construction is one of the fastest growing industries in the United States. At least 10,000 buildings enclosing more than 650 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.

Basics of Tilt-Up Construction

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. These pages explains the basic methods and skills required for successful Tilt-Up construction.

Benefits of Tilt-Up

You may be surprised at all of the advantages Tilt-Up construction has to offer.

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.

Explore the Benefits of Tilt-Up

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.

Fast Track Delivery - Planning begins with an evaluation of the site. Cost Containment - Engineering is a critical phase of each and every Tilt-Up project. Innovation - Once planning is complete, construction can begin on the floor and

footings Lower Operating Costs - There are a number of ways to form individual panels. Architectural Aesthetics - Patterns or texture can easily be added to the face of Tilt-Up panels. Durability - The use of plastic support chairs instead of steel chairs is

recommended to avoid rusting. Safety - Concrete placement methods for Tilt-Up panels are the same as those for floor slabs. Start thinking about Tilt-Up now!

Durability

You may be surprised at all of the advantages Tilt-Up construction has to offer. 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.

Fast Track Delivery You may be surprised at all of the advantages Tilt-Up

construction has to offer.

Design-build –the fast delivery system for your project where building construction proceeds while the design is developed, speeding completion. Tilt-Up lends itself to this process because wall panel construction can proceed while the rest of the building is 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 are completed 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 in a better work environment, which saves 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.

What wind velocity should panels be braced for?

Most panels are designed for a 70mph wind in accordance with the TCA's GUIDELINE for TEMPORARY WIND BRACING of TILT-UP CONCRETE PANELS DURING CONSTRUCTION

What safety factor is necessary for brace design? Most designers use a minimum safety factor of 1-½. How many braces are needed per panel?

A minimum of two 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.

When should the braces be attached to the panel? 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. When and how should braces be removed from panels?

The panel should be removed after the roof connections and/or diaphragm are completed. Braces should be disconnected from the floor first, and then carefully disconnected at the top and lowered to the ground. If they are dropped or allowed to slide down the wall, they may be damaged.

Is knee bracing and cross lacing of braces a good idea? It complicates and prolongs the lifting because it must be in

place before the crane is released. While it is expensive to do, it is sometimes necessary on tall panels in windy areas.

Is cable bracing adequate for panels?

If correctly placed and connected, it can be effective. It is more difficult to adjust or plumb panels with cables than with braces, but exceptionally tall panels may require it.

Are there any 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.

What do I brace to if the floor isn't available?

Have a deadman designed for job site conditions, including the soil type and grade elevations.

Can drill-in expansion type anchors be used? Some types can be permitted they are installed per the

manufacturer's guidelines. The majority requires some skill and certainty of setting that is not always obtained. Even when properly set, the working load with a 4-to-1 safety factor on ¾ inch expansion anchors is much lower than the design load of most Tilt-Up braces.

How do I brace and shore 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.

What is the best method for analyzing a panel in a two story or multistory building design?

It is conservative and perhaps most common to design multi-story Tilt-Up panels as simple spans between supports while accumulating axial loads from the stories 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-story 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-story panels.What is the recommended floor thickness?

A minimum of 5 inches is recommended to provide adequate brace anchorage and permit the crane to operate on it without damage. The use of the crane on the slab, however, does require attention to the load transfer through the outriggers and the pads they rest on.

What sub-base is recommended under the floor?

This depends somewhat on the soils report, but normally about 6" of crushed rock over 95 percent compacted soil.

Is a moisture barrier required under the floor?

Not under warehouse-type uses, unless specified by the soils report. However, it might be considered in floor areas where floor coverings are used and the water table is high.

What strength concrete, slump and type of mix is recommended in the floors?

ACI 302 – “Guide for Concrete Floor and Slab Construction” has recently been changed to ACI 302.1R-04. This revised guide specifies 3,000 psi compressive strength for Class 1, 2, and 3 floors and 3,500 psi for Class 4, 5, and 6 floors with a maximum slump of 5 inches. Because minimizing shrinkage and resulting slab curl is of prime importance, ACI 302 suggests paying special attention to selecting the best possible concrete mixture proportions. In general, the committee recommends a well graded aggregate mix design with a coarseness factor of 50% - 75% and a workability factor of 33% - 43%. The bottom line is the concrete mix design must have low shrinkage, good finish ability, good place ability and the required strength.

What type of joints and how frequently should they occur in the floors?

The typical floor will have joints both ways at no greater than 20 feet on center. They will be steel keyed cold joints in the long direction and control joints should be performed in the perpendicular direction using "Soft-Cut® International" or similar. The joints should be detailed on the panel layout plans.Read Joints in Slabs as published in the February 2005 edition of Concrete Construction for additional references to key ideas about joints in slabs.

What equipment is needed to cast the concrete floors?

The floor needs to be carefully built to act as the casting bed, the crane platform and the working surface of the building. It must be strong at an early age for the ready-mix trucks and crane, and smoothly finished since it will mirror the panel finish. For these reasons, it needs to be vibrated well and struck off in large widths. The Texas Vibratory Screed does this very well and also serves as a straight-edge for inserting the zip strip joint material. However, any

long screed apparatus can be used in conjunction with good vibration and finishing techniques.

How should the concrete floor be cured?

ACI 302 recommends the use of wet burlap, polyethylene film, combination burlap/polyethylene film or liquid membrane-forming curing compounds. Wet burlap, polyethylene film or combinations of both can result in the formation of salt deposits on the floor slab surface which appear as blotchy stains. If a liquid membrane forming curing compound is selected it must be compatible with the intended Tilt-Up bondbreaker or it will be necessary to remove it prior to application of the bondbreaker. Some tilt-up bondbreakers also serve the dual function of both a cure and bondbreaker. A combination cure and bondbreaker has the added advantage of minimizing the number of different products on the job site and the potential for a mistake.

What can you fill the necessary saw cut joints in a slab with prior to pouring panel on top of it that will not read or "telegraph" on to the face of the panel?

To our knowledge nothing exists that will consistently prevent saw cut joints from telegraphing onto the reflective panel surfaces. The problem boils down to whether you prefer grinding and patching or just patching panel surfaces. Some companies manufacture a vinyl rubber based temporary joint filler, which when properly placed in a saw cut joint, forms a uniform depression on the reflective panel surface which is easily patched using a tilt wall patching compound. Most Tilt-Up contractors would agree that it is far easier to apply a patching compound to a straight and uniform void than to carry a grinder 20-30 feet in the air in order to grind a concrete fin.

For painted faces, filling with silicone has been the most successful material. The ridge created when the bead cures is simply removed with a pass over from a grinder. Patching or sacking products are supplied by a variety of TCA Global Suppliers and can be used as needed to repair the grinding marks and fill any low areas. A durable concrete patching compound should be used that can be sanded with ease.

It is imperative that when preparing slab surfaces to produce an exposed aggregate finish, whether sand-blasted, acid- or power-washed or by other means, the joints in the slab must be concave to produce an “outy” on the surface of the panel. This “fin” that exists on the panel is much easier to grind and blend to the exposed aggregate. It is nearly impossible to patch an exposed aggregate panel requiring more extensive repair work.

Large construction joints are best filled with melted wax. One note on the finishing of panels, however, is that while previously a textured finish was required to hide blemishes, today the advanced technology of concrete placing and patching products allows an extremely smooth finish. A high quality patching product and paint is still recommended.

One contractor put it like this "you can't afford to cut corners because you're always remembered for your last project."

Will the crane damage the floor?

Not if it has been properly constructed with the correct sub-grade and compaction. The crane should extend outriggers when lifting heavy loads, and use rolling outriggers when driving with heavy loads. The crane should not be allowed to get near the edge of the slab, especially when deep fills are used.

How should electrical, mechanical and structural floor penetrations be blocked outs?

Wherever possible, electrical, mechanical, and structural objects should be stopped below the floor surface and the opening filled with sand. Place a thin layer of plaster over the sand and trowel smooth. Coat with bond-breaker to prevent adhesion. Joints in the floor that will have panels cast over them should also be filled with plaster and coated with bond-breaker.

Are isolated or continuous foundations better for Tilt-Up? This varies with soil conditions and the slope of the terrain.

Both can work well, but if there is much panel extension below the floor, the continuous footing will be needed to permit the back-filled soil pressure. If there are a number of openings in the panel, the continuous footing allows better support for the panel. The

continuous foundation also permits getting closer to property lines. The typical design today usually utilizes continuous foundations under the panels.

Where is the best place to cast the Tilt-Up panels?

On the floor slab as close as possible to their final position.

Is there a particular sequence or pattern in which the panels should be cast?

They should be cask 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 lift 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.

What is the best method to form panels?

The edge forms are usually of wood with a bracket or wooden block periodically connected to the floor. These brackets are spaced to reduce deflection in the edge forms during placement. These brackets are glued, nailed, or bolted to the floor, depending upon the acceptability of the required patching to the owner.

How do I hold reinforcing steel and embedment items in placed? All items should be adequately chaired for elevation and wired

in place. If possible, the critical connection inserts should be spaced off the edge form to maintain accuracy. Do not try to wet-set items as the concrete is placed.

What can be done with bolts or dowels that stick up and get in the way of screeding or sacked casting?

Use threaded inserts that are flush with the panels to replace protruding bolts. Use threaded inserts or bent dowels to replace projecting dowels.

How high can you stack panels?

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. It is generally necessary to slide the panels a distance equal to its thickness before attempting to rotate, or it will fall off the stack.

How do you form stack-cast panels?

There are several ways currently in use that have variations of jump forms. 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.

How do you stack-cast 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 trowelled to match the panel surface. Bond-breaker is then applied to the surface to seal it and prevent bonding of the concrete above it.

How do you form small block-outs and feature strips in panels? Wooden, plastic, polystyrene, or metal blocks or strips are

used. They should be non-corrosive and non-staining, firmly fixed in place so they will not move during placement. Those that have to be removed should be tapered for easy stripping.

Should exposed aggregate be cast up or down? With proper care, either can be done effectively. Exposed

aggregate up has the advantage of you being able to see what the aggregate job will look like, but requires patching the lifting holes in the aggregate, and if it is large aggregate, there can be problems with the lift inserts.

If greater than 1½" rock exposure is used, the quick disconnect lifting system cannot be used, and the coil bolt system will require grout pads for bearing to be pieced at each lift insert. Exposed aggregate up will also require that the bracing be attached after panels are lifted, which slows down the lifting procedure. The exposed aggregate down leaves the finish a mystery until after the erection is complete. With aggregate down, the rock can be carefully pressed into a sand bed, and the concrete cast over it.

Care must be taken that workmen finishing the panel, vibrators, or concrete coming out of the ready-mix chute do not disturb the rock pattern. Retarder can be used for smaller exposures

What is the typical thickness of panel?

The minimum thickness for commercial walls is generally 5½ inches with 7¼ inches the most typical thickness reinforced with 1.3 to 2.5 psf of reinforcing.

What is the minimum size building that is economical?

Some as small as 5,000 square feet can be economical, if they are relatively tall. Several small buildings clustered together may also prove economical. Special finishes on the walls, such as exposed aggregate or form liners may make Tilt-Up an economical choice.

What is the minimum height buildings that is economical?

Panels up to 96 feet in height have been used in some areas, but special cranes and spreader bars are required for panels over 30 feet in height. It is generally better to have the panels all nearly the same height and less than 30 feet.

Are there any limits to the number or location of openings?

There is no real limit to the number or location 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-eighth the eave height, or two feet, whichever is less.

What size crane is needed to lift the panel?

It is best to let the crane company determine this, based on the size and weight of panels involved. A rule of thumb for the size, however, is two to three times the weight of the panel.

Are there any site conditions that limit Tilt-Up?

Yes, the following should be considered:

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. What really holds the Tilt-Up panels in place?

The roof structure 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 contraction without cracking. The panels are only positively connected to the roof at their centers near the top.

What information is needed to bid a building, and how long does it take?

With the preliminary floor plan, desired height, wall finishes, mansards, type of roof, preliminary soil report and building code jurisdiction may permit it to be completed in a week.

What information is needed to design and detail a building, and how long does it take?

The finalized floor plan, the soil report and decisions on all the bid options are needed, along with any planning commission requirements. With this information, the design and detailing for plans to submit to the building department will take a minimum of four weeks.

How do you insulate a Tilt-Up wall?

Tilt-Up, much like most structural envelopes can receive insulation on the inside through the use of furring systems or the outside with EIFS. 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 independant from each other except for the connection through the insulation. TCA Member Companies that supply these sandwich systems include Composite Technologies Corporation and Owens Corning.

What is the fire resistance of a Tilt-Up panel?

The fire resistance of Tilt-Up walls is easily referenced and/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. Whether a solid concrete panel or an insulated sandwich panel, Tilt-Up fire resistance can be determined with little effort.

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.

Fire Resistance of Single-Layer Concrete

Walls

(UBC/IBC Tables) 1 hour 1½ hour 2 hour 3 hour 4 hour Aggregate Type Minimum equivalent thickness (inches)

Siliceous 3.5 4.3 5.0 6.2 7.0 Carbonate 3.2 4.0 4.6 5.7 6.6

How are inserts held in place during casting of the panels? They should be firmly wired to the reinforcing steel so that they

won't be displaced during the placing and vibration operations. You should not attempt to wet-set these inserts for any reason.

Are there any precautions necessary with inserts?

They should be accurately located vertically, horizontally and for depth.

They should not be placed closer than one foot from any edge or opening.

They should not be placed in line vertically with the brace inserts that might interfere during the panel setting. The concrete should be vibrated well around the inserts. There should be a positive method of preventing concrete from entering the attachment portion of the insert. If there is need to move a lifting insert, consult the erection engineer for proper relocation.

What are the safety factors for lifting and bracing inserts? The Federal OSHA and American National Standards Institute

use a two-to-one safety factor inclusive of all loads for Tilt-Up, and a four-to-one safety factor for precast lifting inserts. Bracing inserts do

not have a standard, but manufacturers and designers normally Up one-and-a-half-to-one or two-to-one.

Are there any safety checks required with erection hardware?

Make sure all hardware is in good working order, unbent and free of cuts and defects.

If coil bolts are used, be certain all bolts are unbent, have washers, and penetrate clear through the coil. If hardware is used that bears on the panel surface, be certain it bears well, using grout pads if necessary with exposed aggregate or textures.

Any strongbacks or added reinforcing specified for lifting must be correctly in place at the time of the erection. All cables, hooks, swivels, and bails must be free to rotate in the line of action or the load.

What are the tolerances of placing the inserts?

The inserts should be placed within one inch horizontally and vertically, and within ¼" for depth.

Tilt-up Concrete Construction Photos

First Step - Preparing the Concrete Panels' Forms

Prior to the tilt-up construction process beginning, the cement slab is poured to create the floor, where the tilt-

up panels will be created.Photo courtesy of constructionphotographs.com

The first step in creating the tilt-up panels is to draw lines on the cement floor slab where the concrete

panels will be formed and poured.Photo courtesy of constructionphotographs.com

Once the lines have been drawn, workers place brackets to outline where the tilt-up panels' outside boundaries, windows and door openings will be.

Photo courtesy of constructionphotographs.com

http://www.constructionphotographs.com/



Ensuring the exact placement of the cement forms is critical to the success of the project. The tilt-up concrete panels must be sized and positioned in precisely the right dimensions and location.


Workers build the tilt-up panel forms out of wood connected to the braces.Photo courtesy of constructionphotographs.com



Once assembled, the tilt-up construction panel forms create a jigsaw puzzle pattern on the floor slab. But the random appearance to the forms' placement is deceiving; each form is positioned precisely to allow the crews to

tilt them into their final spot in the coming days.Photo courtesy of constructionphotographs.com

Rebar is placed in the completed cement panel forms. Rebar is a critical component of tilt-up construction. The rebar strengthens the tilt-up concrete panels, making them safer to lift into a standing position and more durable

once in place.

Rebar is placed in the completed cement panel forms. Rebar is a critical component of tilt-up construction. The rebar strengthens the tilt-up concrete panels, making them safer to lift into a standing position and more durable

once in place.Photo courtesy of constructionphotographs.com



Workers also position embeds and inserts into the tilt-up panels so they will become part of the tilt-up concrete panels once the pouring takes place.


With the wood forms securely constructed and the rebar and embeds / inserts in place, the tilt-up concrete panels in the photo above are ready to be poured with concrete.




Tilt-up Concrete Construction Photos

Second Step - Pouring the Tilt-up Construction Panels

To create each panel, workers pour the cement into the forms in a manner very similar to the way floor slabs are

poured.Photo courtesy of constructionphotographs.com

Once the cement has been poured, workers trowel the panels for a smooth, consistent finish.


Workers use a variety of equipment, including power trowels, to make sure the panels are level and smooth. These concrete panels will become the exterior (and sometimes interior) walls of the building, necessitating a

consistent smoothness or texture on all the panels.Photo courtesy of constructionphotographs.com




The process for building the forms and pouring the concrete tilt-up panels goes quickly. An experienced crew can take a large project from bare slab to completed tilt-up panels in a matter of two weeks.


Once the concrete has cured, workers remove the wood forms and brackets to leave the tilt-up panels lined up on the floor slab.




Workers do last minute detail work on the tilt-up construction panels, including drilling places for the

brackets to be connected.Photo courtesy of constructionphotographs.com

The tilt-up panels have been fully prepped and are ready to be tilted into place.


Third Step - Tilting the Concrete Panels into Place - Tilt-up Construction!

The tilt-up concrete panels are poured into forms that provide the exact size, shape and door openings to meet the design specifications. The tilt-up panels can be massive; this

cement panel weighs about 50,000 pounds. The largest concrete panel used for a tilt-up construction project

weighed six times as much, over 150 tons.

The moble crane lifts the tilt-up panel and tilts it into position over the footing. The row of concrete panels already in place give evidence to just how fast the process for putting up tilt-up panels goes. An experienced crew can tilt up as many as

30 cement panels a day.



The crane lifts the concrete panel and tilts it into position over the footing. Workers help to guide the tilt-up panel and

keep the braces from getting tangled in the lines.Photo courtesy of constructionphotographs.com

Once the cement panel is set in place, the crew attaches the braces to the slab to keep the panel standing until it is

attached to the other tilt-up panels and the roofing system.Photo courtesy of constructionphotographs.com

Workers help to guide a large mobile crane as it lifts a tilt-up concrete panel into place.


Once the cement panel is set in place, the crew attaches the braces to the slab to keep the panel standing until it is

attached to the other tilt-up panels and the roofing system.




REFERANCES1. Wikipedia.com 2. Tiltup.com3. Tilt-Up Concrete Association4. Civil Engg. & construction journal .

Tilt Up Construction

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