Enhancing predicted shear strength for the assessment of existing concrete bridges

Abstract

This paper presents a method of calculating the enhanced shear capacity of concrete T-beams that arises from the increased concrete contribution provided by the flange overhangs of reinforced concrete (RC) T-beams in positive bending or sagging. The method applies recognised provisions in the Australian Concrete Bridge Design Code AS5100-5:2004 to enhance the prediction of shear strength of concrete T-beams based on failure mechanisms reported in published experimental work. The method is applied to specimens reported in previous experimental studies that report shear failure in RC T-beams in positive bending or sagging. It is shown to yield conservative estimates of shear strength enhancement that arise in a T-beam giving consideration to the flange overhangs. A discussion is provided to outline the application of this method for calculating shear strength of concrete highway bridge decks where T-shaped cross-sections resist an applied shear. The paper discusses the variability that arises in the prediction of shear strength from applying the method. The variability observed in the application is consistent with that observed in shear strength tests used as a basis for code-based formulations. All international codes use a lower value of strength reduction for shear than pure flexure to cater for this. It is recommended that confidence in the method be increased by applying the method to more testing targeted at isolating the flange proportions on the shear strength of RC T-beams in sagging.