Pre-stressing is generally a way to overcome concrete weakness in tension. Generally, the concrete undergoes compression on the top flange and tension at the bottom flange. In pre-stressing the tendons are stretched along the axis and cement is poured, later when the tendons are released the compression is generated at the bottom which tries to counter-balance the compression due to loading at the top part of the beam. The upward force along the length of the beam counteracts the service loads applied to the member. The unique characteristics of pre-stressed concrete allow predetermined, engineering stresses to be placed in members to counteract stresses that occur when the unit is subjected to service loads.
Pre-stressing removes a number of design limitations conventional concrete faces on span and load and also permits the building of roofs, floors, bridges, and walls with longer unsupported spans. This allows architects and engineers to design and build lighter and shallower concrete structures without sacrificing strength. This also helps in the construction of longer spans thereby reducing the intermediate pier construction and making bridge construction economical.
Pre-stressed concrete has experienced the greatest growth in the field of commercial buildings. For buildings such as shopping centers, pre-stressed concrete is an ideal choice because it provides the span length necessary for flexibility and alteration of the internal structure. Pre-stressed concrete is also used in school auditoriums, gymnasiums, and cafeterias because of its acoustical properties and its ability to provide long, open spaces. One of the most widespread uses of pre-stressed concrete is parking garages.