An out-of-plane bending hysteretic model for multi-planar CHS X-connections

The multi-planar circular hollow section (CHS) X-connection is one of common configurations in single layered lattice steel tubular structures. A hysteretic model, including the skeleton model and restoring force model is proposed to simulate the hysteretic performance of X-connections under cyclic out-of-plane bending moments (OPB) generated by vertical seismic action. Exponential function is adopted in the skeleton model and the Ramberg-Osgood function is adopted in the restoring force model. The parameters in the hysteretic model are determined by finite element (FE) analysis and nonlinear regression. Additionally, an improved out-of-plane bending hysteretic model considering the influence of brace axial stress and chord normal stress is developed to simulate the seismic performance of X-connections in engineering practice. The proposed hysteric model is verified by experimental and FE results and the improved hysteretic model can consider the effect of strength degradation.