What is Precast, Prestressed Concrete?

Now. With large-scale precast projects, it’s best to start the process as soon as possible. Even if your project is still in the early stages, a precast trade partner can provide expert insights, help manage construction schedules and timelines, and develop tailored precast solutions to fit your project’s needs and get your structure erected faster. Reach out to a Tindall rep nearest you today to chat about what we can do.

Virtually any structure can be constructed using all precast components. However, certain structures benefit more from what total precast has to offer: cost competitiveness, schedule enhancement, durability, inherent fire resistance, thermal resistance, and sound insulation. The larger the footprint and more repetitive the layout, the more competitive precast concrete becomes. Because the cost of installation is largely dependent on the number of picks with the crane, the larger the pieces set in place, the greater the cost and schedule benefit achieved. Therefore, a multi-level precast structure will have fewer pieces per square foot, as one column or wall panel may support multiple floor levels. Employing the exterior walls for structural support eliminates the redundancy of perimeter framings such as steel columns and beams needed when precast wall panels are only used as cladding. In addition, these panels are fabricated without sacrificing aesthetics and include insulation capability. Modular components, such as those used in correctional facilities, are also very readily used as part of a total precast structure. These precast cell modules may be loadbearing and the exterior walls are able to be architecturally enhanced and contain rigid insulation making them an integral part of the building envelope.

After the precast components have been fabricated at one of our precast manufacturing facilities, the pieces are shipped on trailers to the construction site. The precast components are lifted into place using a crane according to an engineered sequence to ensure stability during construction. The precast drawings depict not only the construction sequence but the details of each connection of the final structure. Some building components, such as corbels, are pre-purchased, but much of the hardware necessary to build the structure is prefabricated at our precast manufacturing facility and shipped to the site ready for use. Tindall’s philosophy is to augment any third-party inspection with structural observation visits by our design engineers. This ensures that the structure has been built in accordance with the design intent.

Precast concrete construction offers a wide range of scheduling and safety benefits. The precast components are manufactured in environmentally controlled production facilities. This ensures that each element meets stringent quality control standards prior to being shipped to the job site. The precast concrete manufacturing process can be scheduled concurrently with the foundation and other on-site construction activities. Once delivered, all components including prestressed elements are erected rapidly with minimal lifts, contributing to significantly shorter construction schedules. Another benefit of precast construction is that it provides quicker access for other trades to complete their work earlier, further expediting the overall construction process.

Precast eliminates the need for shoring, scaffolding, and large installation crews, making site conditions substantially safer when compared to other construction processes. Precast concrete also dramatically reduces waste and debris, further reducing on-site safety hazards. This means that precast structures can be delivered and erected without substantial time investments for the setup and maintenance of general conditions.

Yes. Precast is widely considered to be one of the most sustainable construction materials on the market, making it a go-to option for many builders and architects seeking Leadership in Energy and Environmental Design (LEED) certification. Due to its low water-cement ratio, precast concrete is incredibly durable, and the thermal mass of concrete provides inherent insulation that helps reduce the need for mechanically assisted heating and cooling.

Another important factor in precast sustainability is the reduction in construction waste on-site. Precast construction helps reduce on-site debris, eliminates redundant members, and dramatically improves on-site safety by minimizing the size of the crew required to erect a structure.

Yes. Precast wall panels can be designed as both load-bearing walls and shear walls to provide lateral resistance for wind or earthquake loads. Precast wall panels typically have a minimum wythe (exterior or interior concrete layer) thickness of 2 1/2 inches, with greater thickness when needed for structural requirements. Precast panels may be designed as composite or non-composite, depending on the gravity load carrying requirements, as well as the applied wind forces.

Typically for load-bearing members, full composite action of the precast panel is desirable. The two wythes are tied together through the insulation layer to act together to resist loads. Thin wire steel trusses, as well as certain non-metallic proprietary systems, may be used to tie the panel together.

Experience and thermal imaging have both shown that a nominal amount of steel crossing the insulation boundary has minimal impact on thermal performance in precast structures. Solid concrete sections are typically avoided, especially between roof and floor. While tests have shown sufficient adhesion may exist between the concrete and the insulation to provide some degree of composite action, potential degradation of that interface suggests it shouldn’t be counted on for design purposes, as it may result in long-term serviceability issues.

Yes. Insulated precast wall panels are often a key component of thermally efficient building envelopes. Precast walls, with their high thermal mass, have an advantage over lighter-weight materials due to the ability to store and release heat as the temperature fluctuates. This is recognized in the International Energy Conservation Code, the insulation R-value requirement for mass walls is less than other buildings due to their ability to store and release heat.

Precast wall panels with rigid insulation between two layers of concrete provide superior thermal performance by incorporating the required insulation in the exterior skin of the building. High R-values are achievable based on the type and thickness of insulation used.

In addition, precast walls reduce schedule time because the insulation is installed in the panels rather than being applied by another trade.

Yes. The major advantage of utilizing a precast floor system is the benefit provided by the prestressed, precast concrete elements themselves. Precast floor systems achieve longer spans and carry greater loads at shallower depths than other floor systems. Precast components also have inherent fire resistance, noise reduction, and vibration damping characteristics superior to most other materials.

Another major advantage of using a precast floor is the scheduled time gained by having the floor members installed at the same time as the exterior precast facade and interior framing. The speed of precast construction is vastly superior to other types of construction. Reducing coordination by using a sole provider for the structure is another benefit to the design and construction team.

Yes. Weight is precast concrete’s greatest asset in reducing the intensity of the vibration produced by airborne sound from one side of the member to the other. The member stiffness and vibration damping capability are other factors that make precast and prestressed concrete a superior construction material as it pertains to STC.

Precast walls and floors generally do not need additional treatments to provide adequate sound insulation. Charts and graphs showing results of acoustical tests of both airborne sound and impact insulation of various precast components are available in the PCI Design Handbook.

Yes. When the precaster is brought on board in the early stages of design, a significant level of accommodation can be made for cast-in items and blockouts in the precast members. This is especially evident in design-build projects, where a team of subcontractors works with the general contractor/construction manager and their designers to plan for cast-in openings, electrical conduits and boxes, drains, and other items required in the structure. By doing this as part of the prefabrication of the structural precast components, significant time and expense can be saved over performing this work on site. Prestressed, precast members are typically cast on long forms, so repetition is key to getting the most out of this approach. In any project involving precast concrete components, engaging the precaster and contractor as early as possible will provide the most cost-effective solution.

Yes. One precast member that may be used is a Bulb T which Tindall has used for roof spans of approximately 100 feet with a member only 28 inches deep. The Bulb T resembles a double tee with an enlarged “bulb” at the bottom of the stem. This bulb allows for more prestressing strands lower in the member which increases the capacity and allowable spans. Another precast member that may be used is a deep double tee. Precast double tees with depths of up to 4’-0” have been used for heavy loads such as those required for data center construction and manufacturing facilities. Both member types allow for large open areas unobstructed by columns.

Yes. Precast concrete components can be designed to meet any degree of fire resistance required by building code or project specifications. Unlike other building materials, precast concrete is non-combustible and does not appreciably lose strength under elevated temperatures.

As can be proven by code-approved empirical data or by calculation procedures, the steel reinforcing within the concrete, protected by the concrete cover, retains sufficient strength to support the design loads during a design fire. As defined by ASTM E-119, this is proof that the component meets the structural end-point criteria. The heat transmission end-point, or the ability of a component to inhibit temperature increase on the unexposed surface from exceeding a certain temperature gain from the side exposed to fire, is a function of the thickness and the type of aggregate used in the concrete. This information is readily available from graphs that show the thickness required for a given fire endurance by aggregate type, which has been derived from furnace tests per ASTM E-119.

Yes. For any type of construction, the more robust the material used to build the structure, the more capable it is to withstand the impact of weather events such as hurricanes or tornadoes. Precast structures are resilient. They not only remain standing through an event while protecting human life but also can quickly be placed back into service. The mass of a precast structure makes it very stable when resisting lateral forces, no matter the magnitude.

Each precast component is designed to withstand the localized forces, while the connections between the precast components are designed to tie the structure together. In addition to the direct pressure and the suction applied to the walls of a structure, precast concrete is more capable of withstanding the upward suction on the roof, particularly compared to a steel deck roof.

Prestressing precast concrete allows the individual components to absorb loads applied to the surface and regain most or all deflection experienced under load. Prestressing also helps provide resistance to wind-borne debris with minimal damage.

Yes. The two most common design methods for progressive collapse are Tie-Force and Alternate Path. Either method may be employed in total precast structures in much the same manner as cast-in-place concrete by adopting an emulative approach.

In Tie-Force for progressive collapse, the building elements are tied together with tension ties, in accordance with Unified Facilities Criteria, to ensure the overall system has enhanced continuity, ductility, and structural redundancy. For a precast system, this is achieved with a poured-in-place topping containing the required amount and placement of reinforcing steel. In addition, the vertical elements are tied to the topping.

In the Alternate Path progressive collapse method, the vertical load-bearing system must be capable of having one of the elements eliminated, while still supporting the structure to resist both localized and progressive level-by-level collapse. Either the floor/roof system must be sufficiently rigid to span the void created by the missing support element or the framing beams must be connected to accommodate the double span created by the elimination of the common support.