Prestressed concrete is reinforced concrete in which internal stresses have been introduced to reduce potential tensile stresses. How is the prestress commonly introduced?

• A. Tensioning the Tendons
• B. Increasing Cement Content
• C. Widening the Reinforcement
• D. Heating the Concrete

Answer: (A)

Prestressing introduces compressive stresses in concrete by tensioning internal steel tendons. This compression counteracts the tensile stresses that occur under loads, helping to keep the concrete from cracking and allowing longer spans or smaller sections. The common approach is to tension the tendons inside the member, either by pretensioning the steel before pouring the concrete (tendons are stretched and then the concrete is cast around them) or by post-tensioning after the concrete has gained strength (tendons run through ducts, are stretched with a jack, and anchored in place). In both cases, the applied tension in the tendons transfers into compressive stress in the concrete, which is the essence of prestressing.