Stresses in External Tendons at Ultimate

This paper presents the research that led to the development of the equation for predicting stresses in unbonded tendons at ultimate that is currently embodied in the AASHTO LRFD Specifications and AASHTO Guide Specifications for the Design and Construction of Segmental Concrete Bridges. The research, performed by the late Robert J. G. MacGregor, involved the construction and testing of a 1/4 scale model of a three-span, continuous, precast segmental-concrete box girder bridge, erected using span-by-span techniques and post-tensioned with external tendons. This paper presents the results of the tests to ultimate that were dominated by flexural behavior. MacGregor developed an equation for predicting stresses in unbonded tendons at ultimate. Predicted tendon stress increases are compared to a large data base from other tests of beams and slabs with unbonded tendons. The equation results in conservative predictions of stresses at ultimate and provides a rational approach to predicting stresses in tendons that are continuous over multiple spans. [PUBLICATION ABSTRACT]