Overview of Prestressed Concrete
Concrete has significant strength, but its bending strength is very limited. Thus, designers use reinforcement in conjunction with concrete to make useful substances in buildings. Researchers have found out that bending stresses could be eliminated in concrete buildings by adding sufficient compressive stresses to balance them out. Then the element would have a stress distribution throughout that consisted of compression only.
Below sum shows a simply-supported beam with an applied distributed load w 1/4 800 lb/ft. The cross section of the beam is b 1/4 12 in. and h 1/4 18 in. If this beam is made of a similar elastic material, the stresses can be calculated as follows:
This value represents the constant pressure at the top edge of the section, and a similar magnitude of pressure at the bottom edge. Based on the discussions on the compassion strength of concrete , we end it that a plain (unreinforced) concrete beam would fail under this load.
Advantages of Prestressed Concrete Structures
One major advantage of prestressing is that it prevents cracks in the concrete structure by either limiting or completely eliminating tensile stresses in the structure. But prestressing has another very important advantage. Prestressed structural elements can be much deeper than normal reinforced concrete elements for the same span and loading conditions, while still maintaining good deflection ratios.