Flexural Performance and Failure Modes of NSM CFRP-Strengthened Concrete Beams: A Parametric Study

The flexural performance and failure modes of concrete beams, strengthened with near-surface mounted (NSM) carbon fiber-reinforced polymer (CFRP) strips were investigated. For this, reinforced concrete beams (150x250x1400mm) were cast, and cured for 28 days, then strengthened with NSM CFRP strips at varying numbers (1-3), lateral spacing (50-100mm), and embedment lengths (150-450mm). The impact of staggering of NSM CFRP strips upon strengthening efficiency was tackled, as well. The flexural mechanical response, strain in strips at failure, and cracking and failure modes were evaluated for all concrete beams under a four-point loading test setup. The findings indicated that inserting NSM CFRP strips at a certain lateral distance from the main steel bars prevented end-cover peeling-off. Furthermore, staggering NSM CFRP strips contributed to increasing the residual flexural capacity and toughness of strengthened beams by as much as 30 and 51%, respectively, although it led to a slight reduction in their ductility. In general, the present study confirmed the findings of different literature works with regard to the effect of key repair parameters using NSM CFRP strips.