Carbon textile-reinforced concrete jacketing for strengthening of pre-cracked RC beams: role of shear span-to-effective depth ratio

This study investigates the effectiveness of carbon textile-reinforced concrete (CTRC) jacketing for strengthening pre-cracked reinforced concrete (RC) beams, with emphasis on the influence of the shear span-to-effective depth ratio (a/d). Twelve beams with a/d ratios of 1.6 and 2.3 were tested, comprising four unstrengthened control beams and eight pre-cracked beams. The latter were preloaded to approximately 80% of the corresponding reference capacity and subsequently strengthened with U-shaped CTRC jackets using two or three textile layers. Structural response was assessed through load–deflection behavior, reinforcement strain, and crack development, supported by nonlinear finite element analysis. CTRC jacketing significantly improved the residual load-carrying capacity and stiffness of damaged beams. Ultimate load increased by 35–51% for a/d = 1.6 and 68–93% for a/d = 2.3 compared to unstrengthened specimens. Increasing the number of textile layers further improved load capacity and crack control, although diminishing strength gains were observed at higher reinforcement levels. At low a/d, a predominantly direct strut-and-tie mechanism develops, with CTRC providing supplemental tensile ties. At higher a/d, load transfer becomes more distributed, with CTRC bridging multiple cracks and promoting tensile-force redistribution. The numerical model reproduced the overall experimental response and supported the proposed load-transfer mechanisms.