Combined bending and torsion behavior of externally strengthened RC beams via enlargement section and hybrid reinforcement

Abstract

Despite extensive studies on reinforced concrete beams with fiber-reinforced polymer sheets, uncertainties persist regarding their behavior under complex torsional bending loads. This study investigated the combined bending and torsional behavior of RC beams externally reinforced by hybrid expansion and reinforcement sections. In this research, nine beams were cast using normal-strength reinforced concrete (NSC), with cross-sectional dimensions of 150 x 250 mm, and a total length of 1750 mm. One beam was left untouched to serve as a control specimen, and eight of them were reinforced using a sectional expansion technique using self-consolidating concrete (SCC) reinforced with steel, glass fiber reinforced polymer (GFRP) or hybrid reinforce (steel and GFRP). The eight samples were classified into two groups. The first group included 4 samples with a magnification section of 50 mm (∆h = 50 mm) and the second group included 4 samples with a magnification section of 75 mm (∆h = 75 mm). Nine beams were subjected to combined torsional bending loads, and tests focused on the effect of raising the ∆h value, which increases the effective depth, and the GFRP replacement ratio (0% to 100%). Finally, the two groups’ samples were compared for ultimate torsional strength, torsional moment, bending moment, and maximum torsion angle. Expanding the section (∆h = 50) resulted in a 33.33% to 66.67% increase in bending and torsion resistance compared to the control sample. For specimens with an expanded section (∆h = 75), the combined torsional and bending strength increased from 60% to 100%. Due to GFRP’s brittleness, increasing the replacement ratio decreases the specimens’ capacity to resist combined bending and torsion.