Prestressed concrete is a form of concrete used in construction which is “pre-stressed” by being placed under compression prior to supporting any loads beyond its own dead weight. This compression is produced by the tensioning of high-strength “tendons” located within or adjacent to the concrete volume, and is done to improve the performance of the concrete in service. Tendons may consist of single wires, multi-wire strands or threaded bars, reinforced and prestressed concrete pdf are most commonly made from high-tensile steels, carbon fiber or aramid fiber.
The essence of prestressed concrete is that once the initial compression has been applied, the resulting material has the characteristics of high-strength concrete when subject to any subsequent compression forces, and of ductile high-strength steel when subject to tension forces. Prestressed concrete is used in a wide range of building and civil structures where its improved performance can allow longer spans, reduced structural thicknesses, and material savings compared to simple reinforced concrete. Typical applications include high-rise buildings, residential slabs, foundation systems, bridge and dam structures, silos and tanks, industrial pavements and nuclear containment structures. First used in the late-nineteenth century, prestressed concrete has developed beyond pre-tensioning to include post-tensioning, which occurs after the concrete is cast.
Tensioning systems may be classed as either monostrand, where each tendon’s strand or wire is stressed individually, or multi-strand, where all strands or wires in a tendon are stressed simultaneously. Whereas pre-tensioned concrete uses tendons directly bonded to the concrete, post-tensioned concrete can use either bonded or unbonded tendons. Pre-tensioned bridge girder in precasting bed.
Pre-tensioned concrete is a variant of prestressed concrete where the tendons are tensioned prior to the concrete being cast. The concrete bonds to the tendons as it cures, following which the end-anchoring of the tendons is released, and the tendon tension forces are transferred to the concrete as compression by static friction. Pre-tensioning is a common prefabrication technique, where the resulting concrete element is manufactured remotely from the final structure location and transported to site once cured. It requires strong, stable end-anchorage points between which the tendons are stretched.
These anchorages form the ends of a “casting bed” which may be many times the length of the concrete element being fabricated. This allows multiple elements to be constructed end-on-end in the one pre-tensioning operation, allowing significant productivity benefits and economies of scale to be realised for this method of construction.