Shear fatigue life of injected bolted connectors in GFRP sandwich web core panels: Effects of load ratio and aging

The durability of bridge connections is critical for the long-term performance of bridge systems with GFRP composite decks. This study investigates the shear fatigue behaviour of injected Steel Reinforced Resin (iSRR) connectors embedded in FRP composite decks, through a series of fatigue tests performed under different load ratios and exposure conditions. Twenty-four connectors are examined: twelve unaged reference specimens, eight specimens tested under varying R ratios, two connectors with deck parts submerged in water and two subjected to outdoor aging, both for a duration of one year. The results show that, despite the composite nature of the connector, the load ratio and mean load level have minimal influence on fatigue life. Instead, fatigue performance in the high-cycle regime is governed primarily by the applied load range. A unified F-N curve including all R ratios was developed, demonstrating the consistency of this trend and enabling fatigue-life prediction across different loading conditions. Environmental exposure led to measurable stiffness degradation but did not significantly alter fatigue life. These findings highlight the robustness of the iSRR connector and support its application in durable GFRP-steel hybrid bridge systems. • Shear fatigue behaviour of iSRR connectors is experimentally investigated under varying load ratios and environmental exposure. • A unified F-N curve is established across all R ratios, with a regression slope of –9.36. • Prolonged water immersion significantly accelerates stiffness degradation and reduces fatigue life. • Outdoor aging has a negligible effect on fatigue performance compared to unaged reference specimens.