Finite Element Analysis And Experimental Research For Seismic Behavior Of Specially Shaped Knee Joint In RC Frame

With the diversification of architectural style and fuction of using,the special shaped knee joints such as joints between big beam and small column and joints between small beam and big column in RC frames are used increasing in the project, and the research on these joints is few at home and abroad. In order to verify the applicability of knee joints between big beam and small column to design and construction measures with the current standard, this study carried out as follows:â‘ Two different planar knee joints KYJ-1 and KYJ-2 with the ratio of beam height and column height was 2 and 2.5 were tested under reversed cyclic loading, and the seismic behaviors, failure mode and force-mechanism have been compared with test results of regular size knee joints.â‘¡Briefly described the basic theory of FEA.The models of KYJ-1 and KYJ-2 using concrete damaged plasticity were analyzed under monotonic loading and repeated loading by using ABAQUS software; According to the nonlinear analysis and comparison with the tested results of regular size knee joints ,the force mechanism of the knee joint was studied ,and the effect of factors such as concrete strength , strength of longitudinal reinforcement , stirrup ratio and joint sizes on mechanical behavior of knee joints between big beam and small column was examined.Compare the test results with finite element analysis, the conclusions of this paper are summarized as follows:â‘ Force-mechanisms and fracture characteristics of shaped knee joints are similar with regular size knee joints before the yield and are different after the yield. The higher proportion of the high between beam and column is, the more difference is.And damaged region of joints changed from the corner region to regional bond failure. Failure mode is bending failure along the surface occurred by bond-type damage, take the place of shear failure. When the ratio between beam stiffness and column stiffness is larger, the combination of deformation and damage region of speciment may be concentrated in column nose with small column stiffness.â‘¡The ultimate load of specially shaped knee joints is much bigger than regular size knee joints,so that reinforcing steel of coulmn in joints especially straight anchor bar is so likely to cohesive failure between bar and concrete that capacity of joint is decreased rapidly.And the seismic behavior of specially shaped knee joints is lower than regular size knee joints.â‘¢The finite element analysis of factors affecting the joint shows that:1)The increace of concrete strength is in favour of the improvement of bearing capacity and ductility of joint,and increasing degree is depends on size of joint and way lapped of negative moment reinforcement ;2)The increace of volume reinforcement characteristic value is advantage to the improvement of bearing capacity and ductility of joint,without enough shear stirrups. 3)All other factors being equal, using high-strength steel ,the stiffness of joint is degradate and deformation of joint is increases; 4)Eccentric beam-column will ruduce bearing capacity and ductility of joint.