Nontraditional Limitations on the Shear Capacity of Prestressed Concrete Girders

Code based shear design provisions principally use a sectional force design procedure in which it is assumed that plane sections remain plane. However, the shear capacity of a member may be limited by other shear related phenomena that are not captured in codes of practice. These nontraditional limitations on the shear capacity of a member can result from incorrectly evaluating the shear stress that needs to be transmitted across a crack, shearcompression failure along a web-flange interface, or insufficient capacity of longitudinal tension reinforcement at the support. A series of 20 shear tests were completed on ten 52-foot long and 63-inch deep prestressed bulb-tee bridge girders cast with high-strength concrete. An extensive amount of experimental data was gathered and advanced data analysis tools were utilized to evaluate these nontraditional limitations on shear capacity. It was determined that interface shear transfer resistance in high-strength concrete is predicted well by relationships developed from tests on normal-strength concrete specimens. It was further observed that the angle of web-shear cracking was generally steeper than the angle of principal compressive stress as given by the AASHTO LRFD Bridge Design Specifications. This difference in angles creates a significant shear demand on a crack that is not accounted for in the LRFD Specifications. A method is presented for determining if a shear-compression failure along a webflange interface is a potential mode of failure for a prestressed bridge girder. This approach provides a means of calculating the shear stress that must be transmitted across the interface as a function of the geometry and loading on the member as well as a means of calculating the shear resistance along the web-flange interface. This method can be used to guard against a shear-compression failure by placing a limitation on the maximum shear capacity a member. It was also determined that the requirement for longitudinal tension reinforcement near the support included in the 4th edition of the AASHTO LRFD Bridge Design Specifications may underestimate the demand on longitudinal tension reinforcement. Alternatively an equilibrium based approach is presented for determining demand on longitudinal tension reinforcement near the support.published or submitted for publicatio