prestressing is the deliberate creation of permanent internal stresses in a structure or a system in order to improve it’s performance under service loads. Such stresses are designed to counter act those induced by external loading. The application of prestressed concrete is widely used and is in away a natural result. Concrete is strong in compression and weak in tension. Prestressing the concrete would produce compressive stresses which will counteract tensile stresses induced by external loading, thus producing a crack-free material during service-steel is strong in both compression and tension. The benefits of prestressing composite steel beam are to increase the elastic strength, to reduce deflection with limited member depth, to reduce steel weight, to increase ductility by redistribution of internal stresses, and to improve fatique strength of a structural detail by reducing the tensile stress range.
Presteressing mechanisms and bending behaviour of prestressed steel beam are very important to fully utilize the member section. The analysis equations for the elastic state and fully plastic state are developed based on equilibrium of forces and compatibility of deformation. The comparison between bounded and unbounded tendons shows that the bond of the tendons in prestressed steel beams has small effect in improving their behavior. Beams with draped tendons are compared with beams with straight tendons. Draping the tendons reduce the shear stresses in the beam. The magnitude of the reduced shear stresses depends on the depth of the beam and the tendon profile.