Failure mechanism of FRP-steel bonded-bolted hybrid connections after seawater exposure

Abstract

This study investigated the degradation behavior of FRP-steel adhesive-bolted hybrid connections in double-shear joints under various seawater exposure conditions: original salinity seawater with wet-dry cycles (1WD), triple salinity seawater with wet-dry cycles (3WD), and triple salinity seawater immersion (3IM). Quasi-static tensile tests delineated five distinct stages and three mechanical parameters—elastic limit, first peak, and second peak. Seawater exposure induced a decline in these parameters, with prolonged exposure exacerbating the deterioration. The most pronounced degradation occurred under 3WD conditions. A predictive model for elastic limit degradation was established, utilizing the final degradation rate (R_e-min) as a comprehensive index. The highest R_e-min of 1207 N/(30 d) was observed for 3WD at a pre-tightening torque of 1 Nm, while the lowest, 201 N/(30 d), was recorded for 1WD at a torque of 7 Nm. Stable degradation rates were significantly higher in 3WD and 3IM compared to 1WD. Additionally, the degradation rate was influenced by bolt pre-tightening torque, with higher preloads mitigating the rate of degradation. This study offers valuable insights for structural engineering, aiding in the design of more resilient and durable marine structures.