Ultra-low cycle fatigue performance of grid structure with bolted spherical joints

Abstract

This study aimed to investigate the effect of the specification of each grid structure component on the ultra-low cycle fatigue performance of the rod element of a grid structure with bolted spherical joints. Thus, an ultra-low cycle fatigue test of three identical composite steel tube and bolted sphere specimens was performed. The test was performed under three kinds of constant amplitude loading regimes for large axial cyclic plastic strain loads. Based on steel ductility damage and initial geometric defects, a finite element simulation of the test was then conducted using Abaqus/Explicit, which was calibrated according to the test results. In addition, parametric numerical simulations were performed to analyze the effects of different steel tube slenderness ratios, bolt diameters, and steel tube wall thicknesses on the seismic performances of the composite steel tube and bolted sphere specimens. The results indicated that the specimen dissipated energy mainly through material damage in the plastic hinge region in the middle of the steel tube. The steel tube slenderness ratio mainly affected the fatigue life and energy dissipation capacity of the specimen. Further, the ultimate tensile and compressive bearing capacity as well as deformation capacity of the specimen both increased with increasing steel tube wall thickness. Finally, the energy dissipation pattern of the specimen was most sensitive to the bolt diameter; thus, the energy dissipation capacity of the steel tube can be fully utilized only by selecting the bolt specification that matches the rod element.