"We're trying to meet people where they are," said John (J.) Seroky, President, High Concrete Group LLC, about a new transportation partnership to bring co-workers from Lancaster to High's Denver, PA precast concrete plant.
The ability to prestress concrete is an inherent advantage of precast concrete that allows the finished material to efficiently resist cracking as well as seismic, wind, and gravity loads using less concrete. Prestressing is most often accomplished in a precast factory under highly controlled conditions. The finished product is then delivered directly to the construction site.
Pretensioned prestressing is an active form of concrete reinforcement commonly used in precast concrete members such as precast walls, double tees, slabs, beams, and other components. The member can be considered to be pretensioned if the strand has been pulled to tension prior to the concrete being poured into the form. Post-tensioned concrete considers a prestressed concrete member with unbonded strand that is pulled to a desired tension most often on the job site.
How Is Concrete Prestressed?
To prestress a concrete member, high-strength steel strand is laid in the form before concrete is placed. The strand is anchored and then pulled until it reaches a desired tension. The amount of tension applied can range from a few thousand to tens of thousands of psi depending on design.
After tension has been applied to the strand, concrete is poured into the form. As it cures, the concrete bonds to the strand. When it hardens to roughly 75 percent of its specified strength, the strand is released and axial compression is transmitted to the cross-section of the member. The piece can then be stripped from the form and moved to storage.
Prestressed Concrete Can Help Resist Service Loads
Pretension prestressing can impart camber to the member that is useful in resisting service loads. This is frequently the case in double tees, which form the driving surfaces in parking structures. The cambered tee deflects slightly as cars drive over it, then returns to its original shape. The prestressed concrete doesn’t crack because the prestressing holds it in compression.
In some precast concrete members, such as walls and sandwich wall panels, no camber is desired. In these cases the strand is placed in the centroid of the wall, or of the wythes, to prevent the introduction of camber. In composite panels, stresses are adjusted so that the prestressing force coincides with the centroid of the composite section. Generally, precasters space strands uniformly across wall panels.
Common Applications of Precast Prestressed Concrete
In addition to the construction of parking garages, perhaps the most common application of prestressed precast concrete is in the building of the flooring in high-rise structures. Because it promotes the use of longer unsupported spans, prestressed concrete is also frequently used in the building of walls, bridges and roofs, which gives architects greater flexibility when designing these types of structures.
Prestressed Precast Concrete Benefits
The many benefits of prestressed concrete include:
Greater load resistance: In comparison to reinforced concrete, prestressed concrete offers greater load resistance. This is because the prestressed process prevents cracking in all stages of loading, while only the portion above the neutral axis is affected in reinforced concrete.
Improved structural integrity: The absence of cracking also reduces the possibility of the underlying steel rusting, while also resulting in a greater capacity for reversal of vibration, shock and stresses.
Faster and more cost-effective construction: Prestressing requires only about 1/3 of the material needed for reinforced concrete. This can result in faster constructions and reduced overall project costs. However, the precast prestressed construction process does require the use of high-tensile strength steel to ensure maximum stability of the finished product.
Reduced project costs: Prestressed precast concrete can offer the advantage of reduced thickness, resulting in a lighter product that can also help to reduce project costs.
High Concrete Is a Recognized Prestressed Concrete Innovator
For decades, High Concrete has been providing innovative precast concrete solutions that are widely used in the construction of high-rise buildings, parking garages, schools, sports facilities and other structures. We can provide a customized prestressed concrete solution that meets your unique project requirements.
To learn more about the many advantages of prestressed precast concrete, give us a call at 877-844-4418 today.