Fracture simulation and constitutive model of shear connections with bolt failure under low-cycle fatigue loading

Bolted shear connections are widely used in steel braced frames. The plate or high–strength bolt in shear connection is prone to low-cycle fatigue fracture under seismic loading. While the plate failure has been well–studied, research on bolt failure remains limited. Therefore, the fracture simulation and constitutive model of shear connections with bolt failure under low-cycle fatigue loading are investigated. The solid model effectively captures the low-cycle fatigue fracture of bolt, while a simplified modeling method–using improved constitutive model–reduces computation time by about 83 %. Based on experimental validation, both models predict shear capacity, low–cycle fatigue life, energy dissipation, and initial stiffness within a 15 % error margin. Parameters of the combined hardening model suited for high–strength bolts of diverse strength grades are given. The ductile damage initiation and evolution curves used in the solid model can provide a valuable reference for fatigue fracture simulation of bolts. It is recommended that the ratio of bolt diameter to the equivalent mesh size should be above 5.5 to make accurate predictions for low–cycle fatigue life and stress. Adjustments of ± 30 % in two damage parameters showed no impact on fatigue life. Under cyclic loading, thread simplification using nominal diameter and 78 % material strength maintains modeling accuracy. The constitutive models for bolted connections in finite element analysis are established through multiple connectors. Furthermore, this study outlines the methodology for determining the constitutive model and the superposition principle of multiple connectors.