Shear enhancement techniques for deep RC beams using self-prestressing heat-activated Fe–shape memory alloy plates

This study experimentally and analytically investigates the enhancement of shear capacity in deep RC beams having shear-span-to-effective-depth ratio of 2.08 using heat-activated iron-based shape memory alloy (Fe-SMA) plates in various transverse configurations. Four strengthening schemes were explored: vertical web-anchored plates, inclined web-anchored plates, wrapped top-anchored plates, and a dual strengthening scheme combining transverse (shear) and longitudinal (flexural) Fe-SMA plates. Fe-SMA plates function as smart materials that transversely prestress and confine beam cross-sections through their shape memory effect, eliminating the need for external prestressing forces. Activation is achieved by heating the plates and cooling them, which induces recovery stress within the anchored plates and transfers it to the concrete as prestressing. In this study, post-processing of activation responses showed an average recovery stress of 371.55 MPa at 200 °C. Five beam specimens, including one unstrengthened control, were tested under four-point loading to evaluate each configuration. Shear performance improved markedly, with maximum load capacity increasing by 33.2–81.6% and shear cracking delayed by 26–37% compared to the control beam. These gains were achieved while employing relatively low external web reinforcement ratios, underscoring the material efficiency of the proposed methods. Notably, the inclined web-anchored and wrapped configurations proved particularly effective, also enabling a favorable shift in failure mode from brittle shear to ductile flexural behavior. Analytical predictions of shear and flexural capacity closely matched experimental results, validating the proposed models. Compared to prior studies, this work achieved superior structural performance, controlled failure modes, and demonstrated greater practical potential for Fe-SMA strengthening systems.