Experimental study of notched steel beams strengthened with a CFRP plate subjected to overloading fatigue and wetting/drying cycles

Abstract

Previous studies have verified that carbon fiber reinforced polymer (CFRP) external bonding is a promising strengthening technique for steel structures. However, the adhesive bonding can be affected by both overloading fatigue and hygrothermal exposure, and the tendency has not been clearly understood yet. In this study, eight notched steel beams strengthened with a CFRP plate were tested under four-point bending after suffering from overloading fatigue and/or 400 wetting/drying cycles (WDCs) with 3.5 wt% NaCl solution. The effects of overloading and WDCs on the strength, stiffness, strain distribution and failure modes are discussed. The experimental results show that overloading fatigue and/or WDCs significantly affect the mechanical properties of retrofitted steel beams. The strength and stiffness of the overloaded damaged beams were continuously degraded by WDCs, whereas the beams without overloading damage only suffered from the first 90 WDCs. As observed from the strain distribution and debonding failure modes, the WDCs initiated debonding along the steel beam/adhesive interface and degraded the adhesive bonding over all the bonding surfaces. Meanwhile, overloading damage mainly occurred near the notch and resulted in bond degradation of the CFRP plate/adhesive interface, which induced salt solution penetration and thus further degraded the adhesive bonding.