Effect of flange geometry on the shear capacity of RC T-beams

Abstract

In reinforced concrete (RC) beams, shear failure is sudden and brittle without prior indication of failure. As a result, extensive research has been conducted over the past century to develop design equations and models that combine the variables contributing to the shear resistance in RC members. Despite that, this essential phenomenon is still the least understood problem in reinforced concrete. In most current design codes, the nominal shear capacity of RC beams comes from superposition of concrete and steel reinforcement. The contribution of concrete in slender beams comes from three sources: shear resisted by concrete in the uncracked compression zone, shear transfer by aggregate interlocking at the edge of the diagonal crack, and dowel action from the longitudinal reinforcement. In most shear design equations, the shear is assumed to be resisted only by the web of the beams by aggregate interlock at the shear crack. The contribution of shear resisted by flanges of T-sections is usually ignored in the shear strength models even though it was proven by many experimental studies that the shear capacity of T-beams is higher than that of equivalent rectangular cross-sections. Ignoring such a contribution result in a very conservative and uneconomical design. Therefore, the aim of this research is to evaluate and compare the shear capacity of RC T-beams using shear strength models available in the design guidelines and the literature. Some of the chosen design models included the flange contribution to the shear capacity, while other models neglected this phenomenon. The models were evaluated against an experimental data base that included slender RC T-beams with different geometry, flexural and shear reinforcement ratios, compressive strength of concrete, and shear span-to-depth ratios. In addition, the effect of the ratio of flange width to the web width and flange thickness to the total height of the member on the shear capacity of the T-beams were assessed. The analytical results showed that the shear capacity is underestimated by most of the current shear strength models. However, the models that were developed in the recent literature to include flange geometry resulted in safe and accurate predictions of the shear capacity of RC T-beams. As a result, it is recommended that the effect of flange is included in the design equations to aid in a more economical design that is consistent with the true capacity of the member.