Polymer-Bonded/Bolted Steel Plates Versus UHPFRC Overlay for Controlling Deflection in RC Shallow Beams with Planted...

Reinforced concrete (RC) joist slabs are common in Middle Eastern buildings, where architectural needs often necessitate planting columns on shallow beams. Although such beams typically satisfy flexural and shear design requirements, their serviceability is frequently compromised by excessive deflections. This study experimentally investigated the effectiveness of polymer-bonded/bolted steel plates versus an Ultra-High-Performance Fiber-Reinforced Concrete (UHPFRC) overlay, applied to the compression face, in controlling the deflection of shallow beams with planted columns. Four half-scale beams were tested under single-point loading, including two unstrengthened specimens to be used as reference beams. The first control beam reflected typical design practice-adequate in strength but exceeding code deflection limits-while the second specimen was designed to achieve similar flexural capacity with serviceable deflection. The remaining two beams were externally strengthened using either steel plates or UHPFRC overlay. Experimental results were analyzed in terms of failure mode, peak load, and deflection response. Both strengthening methods improved bending performance, stiffness, and load capacity, with UHPFRC showing superior effectiveness. Simplified analytical equations provided reasonable predictions of deflection and ultimate load. The findings highlight the potential of compression-side strengthening, particularly using UHPFRC, to enhance the serviceability of shallow RC beams supporting planted columns.