Precast concrete is a versatile structural material and can be used as the structural system of a building, bridge or other structure. Precast structural systems are comprised of a variety of shapes and components. Most of these will fall into categories of beams, columns, or walls. However, since precast is a cast material, essentially any shape can be manufactured to meet a project’s needs. The basic beams and columns are discussed in this section. Precast structural systems are discussed in Building Engineering Resources.
Beams are typically considered structural components and are made in one of three key shapes:
- Inverted Tee Beams
Beams are horizontal components that support deck members like double tees, hollow-core, solid slabs, and sometimes other beams. They can be reinforced with either prestressing strand or conventional reinforcing bars. This will depend on the spans,loading conditions, and the precast producer’s preferred production methods.
Typical sizes: Practically any size needed to satisfy structural requirements
Typical depths: 16 to 40 in.
Typical widths: 12 to 24 in.
Typical span-to-depth ratios: 10 to 20
Finishes: Since beams are cast upright, the bottom, sides, and ledges are cast against a form and will typically be provided with an "as cast" finish that results in a smooth, hard finish. The top of the beam is troweled by the finishing crew and can be smooth, roughened to simulate the finish of supported double tees (as in a parking structure), or intentionally roughened to create a bond with cast-in-place concrete that may be poured on top.
Columns are typically used to support beams and spandrels in applications such as parking structures and precast concrete structural systems of all types. They generally are designed as multilevel components ranging from a single story to six levels or more. Sizes and shapes can vary to satisfy both architectural and structural requirements.
Square or rectangle
From 12 by 12 in. to 24 by 48 in.
Since columns are cast in a horizontal position, three of the four sides are created with a form. These finishes are very smooth and most often remain "as cast" in the finished construction, although they may have an architectural finish and be exposed to view. The fourth side is normally troweled to match the other three sides as closely as possible.
Raker beams are angled, notched beams that support stadium riser units. They are used universally in outdoor stadiums and arenas and in many indoor arenas and performing-arts theaters.
Sizes can vary as required structurally and to match varying riser sections that they support.
16 to 24 in.
Typically, three sides will have an "as cast" finish that results in a smooth, hard finish. The fourth side is troweled by the finishing crew to match the other sides as closely as possible.
Stadium riser components are discussed under Miscellaneous Components.