Effects of temperature variation on intermediate crack-induced debonding and stress intensity factor in FRP-retrofitted cracked steel beams: An analytical study

Fiber-reinforced polymer (FRP)-retrofitted steel structures in service are likely to experience significant temperature variations due to seasonal and diurnal service temperature changes. Even without the material system degradation, such temperature variations may influence the intermediate crack-induced (IC) debonding mechanism in FRP-retrofitted steel structures, mainly due to the interfacial thermal stress induced by the different thermal expansion coefficients of the FRP plate and the substrate steel. This paper presents a closed-form analytical solution for the full-range debonding process of an FRP-retrofitted notched steel beam under combined thermal and mechanical loading. A bilinear bond-slip relationship is used for describing the non-linear property of the bonding layer. The effects of thermal stress on the interfacial stress distribution, the IC debonding load and the stress intensity factor (SIF) at the notch are examined for the FRP-retrofitted steel beam at various service temperatures. The analytical solution is verified through the comparison between analytical and finite element (FE) results. Parametric investigations have indicated that a temperature decrease may lead to a reduced IC debonding load while an increased SIF, and vice versa. Such effect is more significant when a thicker and stiffener FRP plate is applied to retrofit the steel beam.