Experimental Study on the Shear Behavior of UHPC-Strengthened Concrete T-Beams

Ultrahigh-performance concrete (UHPC) strengthening is an efficient technique to improve the capacity of shear-deficient members. However, the applicability of UHPC strengthening on a T-beam has been scarcely investigated, particularly with regard to repair configurations not reaching beam supports involving a higher delamination potential. In this study, the shear behavior of concrete T-beams with cast-in-place UHPC strengthening is investigated with 10 concrete T-beams, including different strengthening configurations, layer thicknesses, and anchors at the repair interface. Beams with a UHPC bottom layer ending before the support are investigated for the first time. Load-deflection, lateral, and cross-sectional cracking patterns in each beam are analyzed. Besides, strain distributions of the beams are recorded and analyzed through a digital image correlation system to distinguish different failure modes. The efficiency of UHPC strengthening for improving the shear behavior of concrete beams is clarified, and recommendations are provided for a UHPC-strengthened beam design to avoid delamination. The testing results show that UHPC strengthening using lateral layers is the most efficient configuration for improving shear capacity and does not increase the sectional height, while a U-shaped jacket configuration is recommended when a substantial increase of beam stiffness is required. A combination of shear and separation failure is found in beams with a UHPC bottom layer ending before the support, and it is, therefore, suggested not to use a UHPC bottom layer alone due to the development of separation cracks. More ductile failure modes obtained with 50-mm lateral layers and a 25-mm U-jacket are suggested. Installation of anchors at the repair interface is recommended to achieve more ductile failure modes.