High-performance hybrid system using pultruded GFRP profiles and replaceable LYP steel links

초록

Despite the significant advantages of fiber-reinforced polymer (FRP) composites, their inherently low ductility limits their application in moment-resisting frames (MRFs), in which plastic hinges typically form at the beam ends. To address this limitation, this paper proposes a novel ductile MRF system that employs pultruded I-shaped FRP profiles for the beams and columns, connected through replaceable steel links. These links are designed to develop plastic hinges in a controlled manner, intentionally confining the inelastic deformation to the steel components. This configuration ensures that the FRP members remain elastic and thereby enhances the energy dissipation capacity of the system. Finite element modelling and a parametric study covering twelve models were conducted to evaluate the influence of the steel link characteristics - including material type, flange thickness, and capacity ratio (psi) - on the overall performance of the proposed hybrid system. The results show that optimally designed links produce stable hysteresis loops with adequate ductility and no degradation in strength or stiffness. The system also exhibits excellent seismic performance when the steel links satisfy the AISC seismically compact flange criteria. Notably, substituting conventional A36 steel with low yield point (LYP) steel increases the system ductility by more than 2.1 times when the link geometry is preserved, and by 1.23-1.38 times when the LYP link thickness is adjusted to match the flexural capacity of the A36 benchmark. Increasing the link flange thickness further enhances the energy dissipation capacity by up to 4.39 times for LYP links, and the elastic stiffness improves by 1.34-1.40 times relative to the A36 benchmark when the LYP link thickness is matched for capacity. A capacity ratio of psi <= 0.7 is identified as the optimal design range, providing the most favorable balance between ductility and energy dissipation while limiting the peak FRP stress to below 0.7Fu. Overall, the results confirm that the steel link acts as an effective ductile fuse, allowing the connections and FRP elements to remain essentially elastic.

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