Influence of Span-Depth Ratio on Behavior of Externally Prestressed Concrete Beams

This paper describes a numerical study on the flexural behavior of concrete beams prestressed with external tendons, focusing on the effect of the span-depth ratio (L/d(p)) on the response characteristics and the ultimate stress in tendons and ductility behavior A nonlinear model, calibrated by the available experimental results of externally prestressed specimens, is used for the parametric evaluation. The results show that the second-order effects of externally prestressed beams with two deviators at third points become increasingly important with the increase of the L/d(p) and that, due to these effects, a higher L/d(p) registers a lower ultimate moment capacity. The effect of the L/d(p) on the ultimate tendon stress is dependent on the type of loading for internal unbonded tendons and on the configuration of deviators for external tendons. The analysis also indicates that, irrespective of second-order effects, the L/d(p) has an insignificant effect on the ductility of beams, and center-point loading mobilizes higher deflection ductility than third-point or uniform loading.