In prestressed concrete, a prestress force is applied to a concrete member and this induces an axial compression that counteracts all, or part of, the tensile stresses set up in the member by applied loading. In the field of bridge engineering, the introduction of prestressed concrete has aided the construction of long-span concrete bridges. These often comprise precast units, lifted into position and then tensioned against the units already in place, the process being continued until the span is complete. Test your knowledge on design of concrete elements, Prepare for GATE , IES and other examinations. This test will also help graduate candidates appearing for interviews.
Design of Prestressed Concrete – Quiz and Interview Questions[mlw_quizmaster_leaderboard mlw_quiz=16]
Unlike in a pre-tensioned member without anchorage, the stress in the tendon of a posttensioned member attains the prestress at the anchorage block. There is no requirement of transmission length or development length.
The end zone (or end block) of a post-tensioned member is a flared region which is subjected to high stress from the bearing plate next to the anchorage block. It needs special design of transverse reinforcement. The design considerations are bursting force and bearing stress. The stress field in the end zone of a post-tensioned member is complicated. The compressive stress trajectories are not parallel at the ends. The trajectories diverge from the anchorage block till they become parallel. Based on Saint Venant’s principle, it is assumed that the trajectories become parallel after a length equal to the larger transverse dimension of the end zone. The following figure shows the external forces and the trajectories of tensile and compressive stresses in the end zone.