Fatigue behavior of sleeved bolted joints with bonded inserts in pultruded FRP profile

Fiber-reinforced polymer (FRP) sleeved bolted joints with bonded inserts have demonstrated improved static performance, but their fatigue behavior remained underexplored, raising concerns in lightweight FRP structures with high live load-to-weight ratios. To address this research gap, this study experimentally and theoretically investigated the fatigue behavior of sleeved bolted joints for the first time. Tension-tension fatigue tests of conventional and sleeved bolted joints in multi-directional FRP profiles were conducted to evaluate the failure mode, fatigue life, energy dissipation, and stiffness degradation. Results show that adhesive filling establishes insert-hole contact at both the front and rear, transforming fatigue failure mode from one-sided bearing in conventional joints to two-sided bearing in sleeved joints. This failure mechanism prevents localized damage by spreading it over a wider region, yielding a significant improvement in the fatigue life of sleeved joints. Forward and backward insert sliding within the hole due to the two-sided bearing mode transformed the load-displacement hysteresis curve to parallelogram-shaped loops, significantly increasing energy dissipation capacity. Additionally, fatigue failure displacements are effectively reduced in sleeved joints due to the substantially enhanced joint stiffness provided by bonded inserts. Finally, linear and non-linear models based on stiffness degradation are employed to predict fatigue life for conventional and sleeved joints, showing good agreement with experimental results. These findings reveal the improvement mechanisms of bonded inserts and highlight the potential of sleeved bolted joints to prolong the service life of FRP structures. • The fatigue behavior of FRP sleeved bolted joints was studied for the first time. • Failure mode was transformed to a two-sided bearing pattern due to adhesive filling. • Fatigue life and energy dissipation were improved due to two-sided bearing mechanism. • Fatigue failure displacement was reduced due to the enhanced joint stiffness. • Predictive models for fatigue life were established based on stiffness degradation.