Influence of low-cycle fatigue loading patterns on the shear performance of headed stud shear connectors

Abstract

Seismic actions exhibit randomness and complexity. In steel-concrete composite structures, headed stud shear connectors may be subjected to either unidirectional or bidirectional low-cycle fatigue loading due to varying spatial positions and stress states during seismic actions, resulting in different shear performances. The shear performance of headed stud shear connectors under bidirectional and unidirectional fatigue loading patterns, as well as different amplitude variation types, was compared through six push-out tests for the first time in this study. The specific shear performance indexes include the failure mode, shear capacity, skeleton curve and residual deformation. A systematic comparison of the performance degradation mechanisms under various low-cycle fatigue loading patterns was conducted though nonlinear finite element modelling. A parametric analysis was performed to evaluate the impact of stud diameter and concrete strength on shear performance under different loading patterns. The results show that although push-out specimens under low-cycle fatigue loading typically fail via stud root fracture. The maximum shear capacity of bidirectional fatigue loading specimens is 8.3 %-16.0 % lower than unidirectional specimens due to faster and larger accumulation of equivalent plastic strain (PEEQ) at the stud’s fracture section. The residual slip follows an exponential function of the cycling maximum slip in the early loading stage, transitioning to a linear relationship once the slip exceeds 1.0 mm. This function is slightly affected by the stud diameter, concrete strength, loading pattern, and direction.