Deformation characteristics of shear-deficient RC beams wrapped with CFRP

Abstract

The shear-deficient reinforced concrete beams generally have brittle failure, which does not use the yielding potential of stirrups. The fiber-reinforced polymer (FRP) retrofit technique can mitigate the shear damage by controlling the fracture process. Present experimental work deals with the response aspects of unstrengthened and strengthened beams as strength, ductility, and strain history. Proposed tests consist of six small-scale rectangular beams with same material properties and reinforcement configurations. In addition, research presents a scaling rule that preserves the physical similarity between constructed samples and existing full-scale beams. The retrofit material is carbon fiber reinforced polymer (CFRP) and covers the external surface of beams in unidirectional (UD) and cross-ply layups. Although whole wrapping is hard to handle in practice, present work uses this method to confine concrete in compressive and improves its crushing ductility. According to results, FRP wrap improves the strength and ductility simultaneously in shear-deficient members dissimilar to flexural retrofit where only strength is improved. At the onset of rebar yielding, longitudinal fibers provide higher hardening stiffness for cross-ply retrofit that UD case in load–deflection curve. FRP skin controls cracking of web and rupture of steel stirrups especially when it is in cross-ply form. UD layup provides the peak collapse ductility, but cross-ply retrofit maximizes the resisted load. Web strain analysis shows that UD and cross-ply retrofits increase the ultimate shear and vertical strains respectively. Therefore, retrofit design procedure should control the safety of web fibers in cross-ply retrofits especially. UD retrofit has bending failure mode with local and deep flexural cracks, but the cross-ply retrofit has bending-shear failure with redistribution of cracks. Web strains of beams with cross-ply wraps reveal a snap-back event versus load raise that is due to partial rupture of the longitudinal CFRP fibers.