Pre-stressed or prestressed concrete is a type of reinforced concrete that has been intentionally stressed during its construction to counteract the expected tensile stresses that may occur when the structure is subjected to loads. Unlike traditional reinforced concrete, where steel reinforcement is added to handle tensile forces, pre-stressed concrete places the steel reinforcement under tension before the concrete is poured.
The process of creating pre-stressed concrete involves the following steps:
Pre-tensioning: In pre-tensioning, high-strength steel wires or cables (known as tendons) are stretched between anchor points before the concrete is poured. The tendons are then anchored securely at the ends. After pouring the concrete, it adheres to the stretched tendons. As the concrete cures and hardens, the tendons try to contract back to their original length, resulting in compressive forces within the concrete. This compressive force counteracts the tensile stresses that would typically develop when the structure is loaded.
Post-tensioning: In post-tensioning, the process is slightly different. Ducts or sleeves are embedded in the concrete before pouring, and the tendons are inserted through them. Once the concrete has gained sufficient strength, the tendons are tensioned using hydraulic jacks and then anchored. As the tendons are tensioned, they compress the concrete, providing the necessary pre-stress.
The use of pre-stressed concrete allows for the construction of longer and more slender members compared to traditional reinforced concrete. It also increases the structural efficiency by optimizing the use of materials, reducing the weight of the members, and minimizing cracking due to tensile stresses. Pre-stressed concrete is commonly used in bridges, high-rise buildings, parking structures, and other large-scale infrastructure projects.