Research On Restoring Force Model Of RCS Composite Joints

Reinforced concrete column-steel beam composite structure, shorted for RCS, is atypical composite structure composed of reinforced concrete column and steel beam.The advantages of the concrete and the steel are displayed sufficiently. So it will beused widely in the future. Because the species of the RCS composite joint structure arevarious, the force mechanism of it is complex and the bond-slip between concrete andsteel is powerful, the research progress of the RCS composite frame joint in the aspectof the calculation theory is slow. At present, the achievements in the study of restoringforce model of the RCS composite frame joint are rare at home and abroad.Based on the test of the reinforced concrete column-steel beam (RCS) conductedby our research group, hysteresis curves of three RCS composite joints with differentdetails are analyzed detailedly. According to the test result, a uniform skeleton curve,expressed by trilinear model is established by using regression analysis. As well as, theequation of the skeleton curve divided by six parts is given respectively. The stiffnessdegradation rules of RCS joints are got through regressive analysis on the circulationsin different loading stages. Then the restoring force model of the RCS composite jointsis obtained. Examples show that the skeleton curve calculated by the restoring forcemodel presented in this paper coincide well with the test curves. It is also concludedthat the restoring force model has a good applicability and can be used for the seismicanalysis of RCS composite frame structure.Based on the finite element software ABAQUS, three RCS composite joints in thetest are simulated. And the differences of the restoring force model got from the finite element software and the test are compared. Besides, by using ABAQUS thequasi-static tests of RCS composite joints with different axial compression ratios anddifferent concrete strengths are simulated. Combined with our group results, how theaxial compression ratio, concrete strength and joint structure affect the seismicperformance of the RCS composite frame joints is analyzed. It is concluded that theseismic performance of the RCS composite frame joints is proved when thecompression ratio and concrete strength are larger within a certain range (axialcompression ratio is less than0.3and concrete strength is below C60).