STRUT AND TIE MODEL FOR EXTERNALLY PRESTRESSED CONCRETE BEAMS

A model based on the strut-and-tie method is presented to predict the strength of simply supported, externally prestressed concrete beams subjected to a midspan concentrated load. The model defines a safe domain within which the beam would not collapse under the applied load. It predicts four possible models of failure, which may be broadly classified into shear-type failure and flexural-type failure. The actual mode of failure depends on the shear span-to-depth ratio of the beam, the ratio of the loading platen width to the beam depth, the longitudinal and transverse reinforcing indexes, the ratios of effective depths of reinforcements to beam depth, and the loading path relating the stress in the external prestressing tendons to the applied load. The model is able to predict the main events leading to the failure of externally prestressed concrete beams. The preidictions of the model are compared with available test results of prestressed concrete beams with and without external prestressing tendons. Good agreement between the predicted and observed values is obtained.