Flexural Performance of RC Beams Strengthened by Carbon Fiber Reinforced Polymer (CFRP) Laminates

Abstract

The use of composite materials and strengthening systems have gained attention for structural reinforcement and strengthening solutions in concrete, masonry and timber structures in need of repair or upgrade. While many studies have addressed external strengthening of undamaged concrete members with various spacing of the wrappings, design considerations such as member cross-section, stirrup and reinforcement ratio, and level of strengthening, little or no information exist on repair of previously damaged members. This paper seeks to consider the performance of prior-damaged reinforced concrete (RC) beams strengthened by externally bonded carbon fiber reinforcement polymer (CFRP) laminates to enhance the beam's load carrying capacity and failure mode. The five (5) beam specimens (1 plain concrete beam, 1 control RC beam-B1, 1 pre-loaded CFRP-B2 wrapped RC beam-B3, and 2 CFRP wrapped RC beams-B4 and B5) of dimensions of 100 mm × 200 mm × 1520 mm were reinforced with two 12.7 mm diameter bars as main reinforcements, two 9.5 mm diameter two-legged stirrups spaced at 150 mm with a clear cover of 25 mm. CFRP strips of width of 25 mm and a length of 400 mm were epoxy bonded to the underside of the CFRP wrapped beams with a centre-to-centre spacing of 120 mm. Ultimate loads, load-deflection relation and failure pattern were recorded for each beam as the beam failure progression and damage states were observed. The results of the study indicate that, 1) there is a marginal increase in first crack and ultimate loads. The first crack load increase was 15-40%, while that in the ultimate load was between 5-18%; 2) the CFRP wrapped beams experienced a flexural mode and found to be due to debonding of the FRP wraps.