Enhancing shear capacity of wide RC beams with planted columns: steel rods vs. conventional stirrups

Reinforced concrete (RC) wide beams supporting planted columns are frequently employed in non-seismic regions, particularly throughout the Middle East, to transfer concentrated gravity loads from upper floor levels. However, inadequate shear reinforcement in older or improperly detailed members makes these continuous load paths highly susceptible to sudden, brittle shear failures. While existing literature extensively documents the shear retrofitting of standard RC wide beams, the specific structural behavior and shear strengthening of wide beams subjected to highly concentrated loads from planted columns remains a significant research gap. This study addresses this by presenting a comprehensive experimental investigation evaluating two practical rehabilitation techniques. An experimental program comprising four large-scale RC wide beams, each measuring 1900 mm in length with a 650 × 200 mm cross-section, was conducted. Two unstrengthened beams served as baseline controls: one intentionally designed to experience shear failure, and another detailed with adequate internal shear reinforcement. The two remaining shear-deficient specimens were retrofitted using either vertically planted steel rods or near-surface mounted (NSM) U-shaped steel stirrups. The structural response of all specimens was critically evaluated based on crack propagation patterns, ultimate load-carrying capacity, load-displacement responses, and internal strain distributions. Experimental results demonstrated substantial performance enhancements; strengthening with planted steel rods and NSM stirrups increased the ultimate load capacity by 65% and 88%, respectively, compared directly to the unstrengthened shear-deficient control beam. Furthermore, analytical models were utilized to predict the theoretical shear capacities of all tested specimens, which demonstrated a highly accurate correlation with the observed experimental laboratory test findings.