General Questions

Precast concrete can be used to design and construct a mixed-use facility faster, cheaper, and better than other alternatives. Precast fabrication takes place in an off-site manufacturing facility, where the economies of factory efficiency improve both the quality of the product and the bottom-line cost.

The precast concrete system provides a faster schedule than conventional framing because the entire structure is erected from the ground through the roof, including the exterior walls, in one operation. There is no need to return with follow-up trades to install the exterior wall system. The components also can be cast while site work is underway.

Integrating the exterior wall with the structural system can eliminate months from the construction schedule while reducing exposure risk to crews by limiting the need to coordinate multiple trades.

The total time needed to enclose the structure and achieve ‘dry-in' provides a huge advantage, especially here in the northeast with our unpredictable and often harsh weather.

The long spans afforded by the precast framing system maximize design flexibility for each tenant and allows for adaptations to future needs.

Precast manufacturers have engineers on staff who are very familiar with the requirements for all activities associated with these needs, including submittals, design, materials, concrete mixes, product delivery, storage, erection, field welding, and attachments.

It is customary for the precaster to perform the final engineering for the products supplied to the job. This includes loads specified by the Engineer-of-Record, embedded materials, handling, and shipping. Additional assistance can be provided throughout the construction phases to optimize design and construction, including:

Component Efficiency: The precast manufacturer can help ensure fast and efficient erection of components through early design consultation. These factors can include:

  • Mix durability and strength
  • Panelization (sizes and layout)
  • Bay sizes
  • Repetition possibilities for reducing form materials and cost.
  • Efficient shipping sizes and configuration
  • Seismic needs for joints.
  • Finish options
  • Connection issues
  • Scheduling, including production timing and sequencing of cranes.
  • Cost data, including assistance in creating a guaranteed maximum price

Design Aid: Precasters can provide designers with valuable input on a number of key design elements beyond simply manufacturing the components. These include:

  • Structural considerations
  • Code compliance
  • Aesthetics
  • Frame analysis
  • Durability

Construction Support: The precast manufacturer can help create an efficient construction process, providing input on:

  • Site restrictions
  • Scheduling
  • Site logistics
  • Owner restrictions
  • Project management

Long-Term Maintenance:All buildings benefit from a long-term maintenance program that ensures the project retains its durability and aesthetic appeal throughout its service life. Your local precaster can help create a maintenance timetable that ensures the structure receives the appropriate attention.

Your precaster can help create a maintenance timetable that ensures the structure receives the appropriate attention.

The total precast concrete system designed for mixed-use buildings is compatible with nearly any building occupancy that would benefit from long-span construction. The framing grid can consist of 30-, 36-, or 48-foot- wide bays that can be 60 feet long. This size creates a more column-free space than conventional framing systems, which increases useable/rentable space and adds design flexibility.

Yes to both. In particular, a precast concrete system can protect against:

Fire: Precast concrete’s organic composition is naturally noncombustible, allowing it to meet fire-code provisions without additional design techniques, coatings, or insulating material. It won’t give off lethal smoke and will maintain its structural integrity even when subjected to intense heat.

Precast concrete provides the basis for a passive fire-safety system, the value of which should not be overlooked. Codes generally emphasize active systems, but those include tradeoffs. Passive systems, based on compartmentalization, provide inherent protection that does not rely on activation. They include noncombustible floors and walls, such as those provided by precast concrete, to construct sections of the building as separate modules that confine fire to a specific area. Once incorporated into the building, these passive systems protect the building throughout its life.

Tornados/Hurricanes: Structures clad with precast concrete perform well against high wind loads, thanks to the durability of the material and the strength of the connections. Precast walls also have been tested to deflect hurricane-force winds and windborne debris.

Earthquakes: Precast concrete panelized systems can meet all seismic-zone requirements. New connection techniques help re-right buildings after a seismic event and minimize structural damage.

Explosions: The dense mass of precast concrete components and the large panels used for cladding help meet federal requirements for blast protection. Precast concrete can also be used to create planters and other barricades at street level that are prescribed by governmental regulations.

Site Risks: The off-site fabrication of precast concrete components enhances safety during construction. It provides a controlled fabrication environment and eliminates several trades from the site.

Design Considerations

Precast concrete construction has the flexibility to create virtually any design shape, curve, or form, thanks in part to such innovations as self-consolidating and ultra-high-performance concrete. Precast concrete is capable of articulating a myriad of design concepts and aspirations. The designer is free to deliver an uncompromised vision for commercial, residential, or specialized structures.

Design flexibility is possible in color and texture by varying aggregate and matrix color as well as size of aggregates, finishing processes, and depth of exposure. Combining color with texture accentuates the natural beauty of aggregates. Many variables will impact the final color and consistency, including the type and color of cement, water-cement ratios, qualities of the coloring agent, batching and mixing techniques, impurities in the aggregates and fine materials, and uniformity in the curing cycles.

Working with their precast manufacturer, designers can specify a variety of aggregate colors and sizes, matrix colors, shape or form details, and surface finishes, as well as the depth of exposure of the aggregates, to achieve a wide variety of textures and meet numerous design objectives.

A wide range of precast concrete surface finishes are available, and two or more often are combined in one panel to create contrast and more interest. The most common finishes include:

  • Smooth or off-the-form finish
  • Exposed-aggregate finish
  • Form-liner patterns
  • Sand or abrasive blasting
  • Acid etching
  • Tooling, spalling, or chipping, usually called bushhammering
  • Hammered-rib or fractured-fin design
  • Sand embedment
  • Honing or polished finish
  • Painting
  • Cost data, including assistance in creating a guaranteed maximum price

Clay products, such as ceramic tile, terra cotta, brick, and other facing products, can be cast integrally. The clay product can cover the entire exposed panel surface or only a portion, serving as an accent band or contrasting section. Granite, marble, glass, and ceramic mosaics also can be cast integrally or applied to the hardened concrete.

The design recommendations for span lengths vary from product to product. These general rules of thumb should be remembered:

  • 6- to 12-inch deep hollowcore plank can span 20 to 40 feet.
  • 24- to 32-inch deep double tees can span 50 to 70 feet.
  • Beams come in variety of size and can span up to 60 feet.
  • Wall panels come in a variety of sizes. A typical wall would be 12 by 30 feet.
  • Columns can be multi-floor. The maximum length for one piece is 40 feet, and it can be spliced in the field for taller structures.
  • Factors such as heavy loads and openings can affect the span capabilities of the system. Your local precaster can determine the given loadings, fire-endurance ratings, span lengths, and slab thicknesses.

Your local precaster can help determined the given loadings, fire endurance ratings, span lengths and slab thickness for your project.

Typically the following information would be provided to the precaster on the drawings:

  • Span directions
  • Loading requirements
  • Connection information
  • Fire resistance requirements
  • Topping requirements
  • Opening sizes and locations

Yes, precast concrete wall panels are almost infinitely customizable and make great alternatives to CMU and steel-frame foundations.

Yes, hollowcore plank can be used to improve energy rating, reduce loads, create larger spans, and provide other positive attributes not easily attained with steel-deck construction.

All precast, prestressed concrete products have excellent fire resistance. Depending on the thickness and strand cover, ratings up to a 4-hour endurance can be achieved. A fire rating is dependent on equivalent thickness for heat transmission, cover over the prestressing strand for strength in a high temperature condition, and end restraint.

Underwriters Laboratory (UL) publishes fire ratings for various assemblies. The fire ratings should be considered in determining the slab thickness to be used during the preliminary design phase. The code does not require that UL listings be provided. These listings are the result of proprietary tests on specific precast units produced and tested by specific companies. If UL labels or numbers are required, the specific details in the UL Directory are exactly and only what will meet this requirement.

Model codes like the IBC have prescriptive fire ratings. This is the best way to indicate ways to accomplish specified fire ratings and should be the first choice.

The PCI manual Design for Fire Resistance of Precast Prestressed Concrete illustrates the code-accepted practice of rational fire design for precast and prestressed concrete products. In the case of hollowcore plank, an equivalent thickness is calculated based on the cross-sectional properties of each brand of hollowcore. Rational fire design is used for situations not covered by the code.

Efficiency and economy in precast concrete construction is driven by repetition, standardization, and minimizing piece counts. Optimum bay sizes are most commonly based on the width of the standard double-tee module being used. A garage manufactured by a precaster who is fabricating 12-inch-wide double tees would optimally use 36- or 48-foot bays. Precasters in the project region should be consulted to determine what modules will be most efficient.

It is most economical to maximize panel size and minimize the number of precast units on a project. This results in fewer erected pieces, connections, and crane picks. However, efficient sizes may require panels of less than maximize size due to a variety of factors.

For example, the size may be limited by site conditions or the reach of the crane used to set the pieces. A site with limited access or one where the maximum panel weights are set by the crane capacity could create overriding factor in determining panel dimensions. Similarly, the size or weight of precast panels may be limited by shipping or fabrication considerations specific to a region or individual precast supplier.

Panels usually should not exceed a width of approximately 12 feet without consideration for a special permit or escort. Panels that exceed 40 feet in length may require prestressing to reduce handling stresses and minimize cracking. The maximum size also is a function of the design loads and locations of building supports.

Not always. While shear walls provide an economical option, there are multiple choices available to provide lateral bracing. These include interior and exterior moment frame systems. Often, discrete placement of shear walls at vertical stair and elevator cores can be effective when combined with moment frames. Your local precaster can provide advice on the most economical solution.

Your local precaster will be able to advise you on the most economical solution for your project.

Design Considerations

Penetrations may be provided in precast concrete products by designing and casting openings into the pieces at the plant, by installing steel headers, or by saw cutting in the field. In laying out openings for a project, the least structural effect will be obtained by orienting an opening parallel to a span.

The general contractor must coordinate with trades to provide the precaster with all pertinent information during the shop-drawing phase so the product can be design to optimize penetrations.

Small openings (less than 10 inches) are typically core-drilled in the field by the involved trade (plumbing, electrical, etc.) after the product has been installed. The location and size of these openings should be provided to the precaster during the shop-drawing phase to ensure accuracy.

Schedules and Cost

A total precast concrete system provides a single-source supplier. There is only one schedule and one field construction management, which minimizes coordination conflicts. The precast concrete components are cast off-site regardless of weather constraints.

Talk to your local precaster regarding schedule and estimates.

Sustainable Design

Yes, precast concrete construction can assist in achieving many sustainable attributes and will contribute toward a variety of LEED rating points. Some of the key contributions include:

  • Precast concrete walls act as thermal storage to delay and reduce peak thermal loads and may help reduce the requirements of mechanical systems capacity.
  • Precast concrete walls used with insulation provide energy benefits that exceed the benefits of mass or insulation used alone in most climates.
  • Precast concrete sandwich wall panels used as an interior surface can save material by eliminating the need for framing and drywall.
  • The raw materials used in precast concrete are generally local and the product is shipped locally as well.
  • Precast concrete walls can be designed to be disassembled for building function changes, saving material and extending the service life of the panels.
  • Precast concrete's durability creates a long life-cycle and low maintenance, which create less need for replacement and maintenance during the building's life.
  • As a plant-cast product manufactured under tight quality controls, precast concrete eliminates construction waste and minimizes transportation and disposal costs.
  • Using plant-manufactured precast concrete components with just-in-time delivery reduces site disturbance and material lay-down requirements.
  • Precast concrete contains recycled steel content and may contain recycled cementitious materials (fly ash or silica fume).

The use of insulated precast concrete wall panels, floor planks, beams, and a variety of other insulated components can maximize the energy rating and enhance the R-values desired.