Prestressed Concrete

Prestressed concrete is a structural material in which internal compressive stress is deliberately introduced during manufacture, so that the concrete is already pre-compressed before it ever carries service loads. Because plain concrete is strong in compression but weak in tension, this built-in compression must be overcome by tensile service loads before any net tension develops in the material, dramatically increasing the effective tensile capacity of a concrete member and allowing longer spans, thinner sections and reduced material use compared with conventional reinforced concrete. The compression is induced by tensioning steel tendons either before the concrete is cast, in pre-tensioning, or after it has cured, in post-tensioning, a method that permits curved or profiled tendon paths tailored to counteract expected loads. The technique was patented by the French engineer Eugene Freyssinet in 1928 and has since become fundamental to modern long-span construction, from bridges to towers to iconic shell and shell-like roof structures such as the Sydney Opera House.