Anchorage of External Tendons in End Diaphragms

Abstract

External posttensioning tendons in concrete box girder bridges are usually anchored in very massive end diaphragms. Several incidences of distress of such diaphragms have been reported in the literature. This paper presents the results of an analytical and experimental research program on design and behavior of end diaphragms when used for the anchorage of external tendons. Finite-element analysis results, strut-and-tie models, and results of a physical test series of half-scale specimens are included. The strut-and-tie model approach is shown to be an effective method to describe the flow of forces in the structure and for design. Ultimate strength predictions based on simple strut-and-tie models were safe but quite conservative. Refined strut-and-tie models based on finite-element analysis results were required to arrive at satisfactory reinforcement arrangements for crack control.