ABSTRACT
The purpose of Prestressed Concrete (PSC) is to minimise tensile stresses by inducing compression. This is achieved by the tensioning of high strength steel strands using hydraulic jacks. The strands usually comprise seven galvanised steel wires twisted together to form a rope. There are two main types: pre-tensioning and post-tensioning. Pre-tensioning involves casting the concrete around tensioned tendons. The chapter focuses mainly on post-tensioned concrete, where the tendons are stressed after the concrete has hardened. Post-tensioning is often used for curved structures. Prestressing strands can be bonded to the concrete using grout injected into the ducts, or they can be left unbonded. Experts in prestressing sometimes allow the section to crack, which is a state known as ‘partial prestress’. There are two types of prestress loss: short-term and long-term losses. Short-term losses occur immediately the tendons are stressed: whereas long-term losses occur during the working life.
