Hysteretic performance of CHS steel members under cyclically fluctuating axial loads and lateral displacement

Abstract

Circular hollow section (CHS) steel members have been widely used in large-span reticulated shells. However, both the axial force and bending moment fluctuate significantly in single-layer reticulated shell members during earthquake events. Therefore, to understand the hysteretic performances of CHS members under a complex loading status, in this study, laboratory tests were performed using eight full-scale CHS samples subjected to combined fluctuating axial force and cyclically increasing lateral drift. Then, the experimental results were compared to those of a numerical analysis. Through full-scale laboratory experiments, ultralow cycle fatigue data for five compressive and three tensile CHS specimens were obtained under different combinations of loading patterns to investigate the different factors influencing the hysteretic behavior of the CHS. These influencing factors include the fluctuating amplitude, frequency, and phase of axial loading cycles relative to unilateral drift. The CHS members under varying compressive axial forces were shown to have a more pronounced global deformation and asymmetric lateral resistance than the members under varying tensile forces. Members under an uncoupled combination of axial load and lateral displacement showed slightly asymmetric lateral force-displacement hysteresis loops. The uncoupled varying axial load and lateral drift slightly influenced the single-cycle energy dissipation capacity of the tensile specimens. However, with a longer fracture life, the total exhausted energy of the tensile specimens increased. In addition, the cyclic void growth model (CVGM) micromechanical fracture prediction theory, which is based on finite element numerical simulations, was also conducted in ABAQUS for comparison to validate the experimental findings. The CVGM theory should not be adopted when the Lode parameters extracted from a “cracked element” are close to 0 in the middle stress triaxiality range with fully developed plasticity.