Experimental And Numerical Research On Seismic Behavior Of S-RC-SRC Composite Frame

To solve the problem of insufficient research on the multi-storey composite frame of steel upper column,steel reinforced concrete lower column and reinforced concrete beam(S-RC-SRC composite frame),the low cyclic load test was carried out on S-RCSRC composite frame to investigate the seismic performance.The experimentallyvalidated finite element model was established by ABAQUS and parametric analysis was performed.Finally,based on the modified angular displacement equation,a practical skeleton curve model and hysteretic model for this type of frame were proposed and validated.The results of test,finite element analysis and theoretical analysis showed that:(1)Under the design principle of "strong column and weak beam",the failure of the three frame specimens was all caused by the plastic hinge failure at the beam end of the second story of steel frame.The hysteretic loops of the three frames were full and smooth before the specimens failed,and the equivalent viscous damping coefficients at their ultimate state were all greater than 0.3,which indicated that S-RCSRC composite frame possessed good energy dissipation capacity.The μ+ of KJ-1(positive ductility coefficient)was 16.03%lower than that of KJ-2.Due to the constraint of the weld quality of the specimen,the energy dissipation capacity of the three frames could not fully display,especially for KJ-3,the fracture of weld occurred when loaded to 5Δy.(2)The numerical results of KJ-1 and KJ-2 were in good agreement with the experimental results.The parametric analysis showed that the improvement of concrete strength had little contribution to the overall horizontal ultimate bearing capacity,but it could increase the initial elastic stiffness and significantly reduce the degree of plastic damage of concrete;The increase of axial compression ratio had a significantly negative effect on the overall horizontal ultimate bearing capacity,but has little effect on the initial elastic stiffness;Reducing the slenderness ratio not only made a significant contribution to the overall horizontal ultimate bearing capacity and initial elastic stiffness,but also helped to reduce the range of plastic region at the bottom of steel columns.(3)Based on the modified angular displacement equation,the second-order elastic stiffness of multi-story composite frame was analyzed,and same for the incremental stiffness matrix and initial elastic stiffness;The practical skeleton curve model was established,and the maximum force PA in the elastic stage,horizontal ultimate bearing capacity PB and the relationship between PA and PBwere investigated.The average error and standard deviation between the theoretically-predicted value and the actual value of PA were 2.59%and 0.0179 respectively,the average error and standard deviation between the theoretical predicted value and the actual value of PB were 9.08%and 0.0553 respectively.(4)Based on the practical skeleton curve model,the hysteretic rule of S-RC-SRC composite frame was established.The stiffness at each stage was quantitatively analyzed by regression analysis.Most of the hysteretic curves predicted by theoretical analysis were in good agreement with the experimental and finite element results,which showed that the hysteretic model proposed in this paper had great practical value and reference significance for analyzing the seismic performance of S-RC-SRC composite frame.