Web-Shear Behavior of Externally Prestressed T-Shaped Beams with Both Positive and Negative Moment Regions

To study the web-shear behavior of a region with an inflection point, five externally prestressed T-shaped beams with overhangs on one side were designed with different shear-span ratios and moment ratios. The specimens were tested to failure under corresponding concentrated loads. By investigating the crack-development behavior, failure mode, and mechanical behavior of the specimens, the following conclusions were obtained: both the shear span ratio and moment ratio could significantly affect the formation and development of diagonal cracks and the redistribution of internal stresses in the specimens. The web-shear failure mode of the specimens could be defined as a shear-compression-sliding failure that was notably different from that of specimens without external tendons. At failure, the concrete in the shear-compression zone was first destroyed in the region with a higher absolute value of moment. Subsequently, external prestressing tendons lost support, retracted elastically, and released a large amount of elastic strain energy. As a result, the two portions of the specimen separated by the failure crack slid against each other. The specimens all failed completely and violently as soon as the ultimate loads were reached. All the stirrups crossed by the critical web-shear cracks were ruptured, and the longitudinal steels in the top and bottom flanges had buckled. The capacity of two design codes to accurately predict the shear strength of the specimens-the ACI Code and the AASHTO LRFD Bridge Design Specifications-was investigated through the experiments performed in this paper.