Cyclic Behavior of Four-Limbed Circular CFST Latticed Beam-Columns

Experimental tests to investigate the behavior of four-limbed circular concrete-filled steel tube (CFST) latticed beam-columns under constant axial compression and cyclic lateral force were carried out. Attention was paid to the effect of diameter-to-thickness ratio of limb tube D/T (51.5 and 24.9), axial compression level n (from 0.05 to 0.5) and type of limb [circular CFST and steel circular hollow section (CHS)] on the overall behavior, failure modes and force versus deformation relationship of the specimens. Additionally, the cyclic deterioration of stiffness, ductility and accumulated energy dissipation of the specimens were assessed for seismic design. According to this experimental study, it is found that, due to the interaction between limb tube and its concrete core, the seismic resistance of composite specimens is better than that of steel counterparts. Moreover, the seismic resistance of composite specimens generally reduces with the increase of D/T and n. A finite element (FE) model is further established to replicate the behavior of the specimens, and the simulated cyclic behavior of four-limbed circular CFST latticed beam-columns subjected to constant axial compression and cyclic lateral force agree well with experimental results. Parametric study on the lateral force versus displacement hysteretic curve of four-limbed circular CFST latticed beam-columns was performed using the verified FE model. Finally, an accurate restoring force model (RFM) to predict the lateral force versus displacement relationship of four-limbed circular CFST latticed beam-columns is developed, and the predictions are in good agreement with the numerical and experimental results.