Shear Response of Prestressed Thin-Webbed Continuous Girders

While different design codes provide similar guidance for the flexural design of prestressed thin:
webbed continuous girders, the shear design provisions differ greatly. This paper investigates
these discrepancies with the help of eleven experiments and a number of analytical studies. Together these provide the basis for recommendations for engineers conducting the shear design for new girders or evaluating the shear capacity of existing girders. It is shown that the traditional ACI approach of taking Vc as the smaller of Vci, flexural:shear cracking load, and Vcw, web:shear cracking load, can significantly overestimate the shear strength of such girders particularly if they are highly prestressed and contain relatively small quantities of shear reinforcement. The other codes evaluated provided more conservative predictions. It is shown that the ACI predictions can be improved significantly by taking into account the effect of flexural stresses on web shear cracking. While the ACI code uses different shear strength equations for members subjected to external axial loads versus members subjected to internal prestressing forces, the studies summarized in this paper support the idea that unification of these ACI shear provisions is possible.