Experimental and numerical research on seismic performance of S-RC-SRC composite frame

The hysteretic behavior of upper steel-beam-to-column and lower RC-beam-to-SRC-column (S-RC-SRC) composite frame was investigated experimentally and numerically in this paper. Two 1:3 scale-reduced three-layer frame specimens (KJ-1 and KJ-2) were manufactured and tested under low cyclic loading. Both the KJ-1 and KJ-2 failed due to the plastic hinge (weld fracture) at the beam end of 2nd-layer. The hysteretic curves were smooth and plump, which indicated that the S-RC-SRC composite frames possessed excellent energy dissipation capacity. The seismic performance index, e.g. ductility coefficient, strength and stiffness degradation and energy dissipation coefficient were analyzed and the results showed that KJ-2 had larger initial elastic stiffness (2.37kN.mm) and slower strength degradation. Experimentally validated finite element models were established and parametric analysis was performed on three factors: strength grade of concrete (M - 1 series), axial compression ratio (M - 2 series) and slenderness ratio (M - 3 series). Ten finite element method (FEM) models were analyzed and the results showed that M-14's (FEM model with C60 concrete) horizontal load-carrying capacity and initial elastic stiffness had limited promotion (all lower than 9%) comparing with the benchmark M - 11 (FEM model with C30 concrete), but M - 2 and M - 3 series varied obviously. Finally, a practical skeleton curve model and hysteretic rule were proposed on basis of the modified angular displacement equation. The theoretically analyzed results were in good agreement with test and FEM results with an average error of 4.90% and 2.59%.