Optimum amount of CFRP for strengthening shear deficient reinforced concrete beams

Abstract

The behavior of shear deficient under-balanced reinforced concrete beams with rectangular cross-sections, which were externally strengthened with CFRP composite along shear spans, was experimentally investigated under vertical load. One of the specimens represents a reference beam without CFRP strengthening and the other specimens have different width/strip spacing ratios (w(f)/s(f)). The optimum strip in terms of w(f)/s(f), which will bring the beam behavior to the ideal level in terms of strength and ductility, was determined according to the regulations. When the w(f)/s(f) ratio exceeds 0.55, the behavior of the beam shifted from shear failure to bending failure. However, it has been observed that the w(f)/s(f) ratio should be increased up to 0.82 in order for the beam to reach sufficient shear reserve value according to the codes. It is also observed that the direction and weight of the CFRP composite are one of the most critical factors and 240 gr/m(2) CFRP strips experienced sudden ruptures in the shear span after the cracking of the concrete. It is considered as a deficiency that the empirical shear capacity formulas given for the beams reinforced with CFRP in the regulations do not take into account both direction and weight of CFRP composites.