Influence of staggered floor and unequal height of left and right beam on seismic behavior of CFSST column-to-HSS beam composite frames

One-third scale models of three concrete-filled square steel tubular (CFSST) column-to-H-shaped steel (HSS) beam composite frames with two bays and three stories were designed and manufactured. A failure test of the specimens under lateral cyclic loading was conducted. The experimental parameters included a staggered floor ratio and unequal depth ratio, staggered floor ratios of 0 and 0.5, and unequal height ratios of 0 and 0.75. The skeleton curves, hysteresis curves, and the stiffness and strength degradation of the CFSST column-to-HSS beam composite frame were analyzed. The results showed that the test frames exhibited excellent seismic performance, and the order is KJ-1, KJ-2 and KJ-3. The drift ratio ranges of δy, δm, δu were 1/123-1/191, 1/37-1/38, and 1/27-1/29, respectively, indicating that the three test frames possessed sufficient ductility and met the seismic objective of not collapsing in large earthquakes. The equivalent viscous damping coefficients of the specimens in the failure stage were in the range of 0.24–0.18, meeting the earthquake protection requirements. A simulation model have developed to predict the P-Δ response envelope. The model results were consistent with the test results.