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Building Engineering Resources

Precast For Buildings

Precast concrete is used for both architectural and structural applications on all types of buildings from low-rise to high rise. The information and resources in this section focus on the structural design of buildings.

A qualified, registered structural engineer should be retained to provide structural engineering services for the final design.

Precast Structural Systems (Total Precast Systems)

Precast concrete is a structural material that can be used as the primary structural system of a building transferring roof, floor, and lateral loads. Precast enables designers to integrate structural and envelope (architectural) systems reducing thetotal materials, detailing, costs, construction complexity and more. Sometimes, this is referred to as "Total Precast Systems, or TPS.

The design versatility of precast concrete allows for almost any shape element such as curved and radial sections, with flexibility in connection points and load paths. High strength, prestressed concrete structural members also deliver exceptional load-carryingcapacity, which can result in smaller sections, longer spans, or both when compared to other structural systems.

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TPS-1

The design of precast, prestressed concrete structures depends on the integration of the structural system as a whole, the connections, and the individual components. Each aspect must consider the others as well as the functional requirements imposedby the building use.

It is essential that design loads follow a load path from their point of origin to the final support or foundation. Although not always required by code, it is desirable to design the members and their connections to achieve a ductile, rather than abrittle, failure mode.

In addition to resisting gravity loads, a principal consideration in building design is the lateral force-resisting system. There are a variety of precast concrete designs that can be used to achieve these goals economically and effectively.

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Precast structural systems can be designed as shear wall, moment resisting, or hybrid systems.

Shear Wall Systems and Load Bearing Walls (interior/exterior)

Shear wall systems use combinations of columns, beams and walls to transfer gravity loads to the foundation, but relay on walls and/or specially designed sections such as an elevator shaft to resist lateral loads such as wind. Precast concrete structuresare mostly designed as simply supported shear wall systems. Shears walls can either be located on the interior, or exterior of the structure.

Shear int
Shear ext

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Moment-Resisting Frames

Moment-resisting frames are those in which a degree of rotational restraint is provided between vertical components (usually columns) and horizontal components (usually beams and/or spandrels). This system then resists lateral loads imposed on the structure.

Moment Frame

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Hybrid Systems

HybridPrecast concrete components can be combined with other construction materials, particularly steel or cast-in-place concrete, to create a "hybrid" system. Examples include architectural precast concrete cladding supported on a structural steel or cast-in-placeconcrete frame as well as precast, prestressed double tees or hollow-core used as the floor system on a parking garage where the main structure is steel.

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Diaphragms

In structural systems the floor and roof components support not only gravity loads, but also act as diaphragm to transfer lateral loads (such as wind and seismic forces). These components also provide bracing to vertical elements and protect them againstabnormal loading.

Precast concrete floor and roof systems can be designed and used as diaphragms. Hollow-core systems may utilize perimeter reinforcing and grouted joints or may use a reinforced concrete topping.

Double tee systems may include untopped or pre-topped tees, pretopped tees with pour strips at the ends, or tees with cast in place topping.

More information on diaphragm design can be found on the PCI Design Handbook.