What is Prestressing?
Prestressing is a method of reinforcing different kinds of structural elements. It was based off of the use of rebar in concrete as reinforcement, with the main distinction being that an induced stress changes the properties of the concrete (PTI). In most applications, prestressing is used to overcome a materials’ weak tensile strength. A highly tensile steel strand or rod passes through the material, is pulled into tension and anchored on both ends to couple their properties. This prestressing applies a compressive stress on the material, which offsets the tensile stress the material might face under loading. A technique of prestressing is called post-tensioning, commonly used in concrete structures, in which the tension is applied after the material is in its final state, such as a concrete slab or a complete structure.
Post-tensioning has been in practice since the early 20th century, but only recently have companies really taken advantage of its structural and financial benefits. For example, to a stronger concrete slab means you can build with less concrete but still retain the same structural properties as a much larger slab without post-tensioning. Less concrete means it will be less costly to manufacture, lighter to ship, and easier to install. It also allows for new designs to take advantage of a lighter concrete slab without compromising its strength.
The method of prestressing has been implemented for several decades in all types of bridges, many kinds of elevated slabs (i.e. residential and high-rise structures, parking garages, etc.), as well as foundations, walls and columns. Post-tensioning has driven the potential for longer bridge spans, larger structures, unique constructions, and more structurally sound buildings (PTI). And because of its “rubber band-like” properties, which are very tolerant to lateral loads, prestressed members have long been used in seismic resistant structures (DSI).