Study On Seismic Behavior Of New Cast-in-situ Joints In Reinforced Concreteframes

Due to its unique advantages,reinforced concrete frame structures have become the most widely used structural form in the field of building structures.The core area of the joint is the weak link when considering structure seismic problem.Due to the problems of design and construction,the traditional reinforced concrete frame structure frame joints have great hidden dangers.Therefore,it is of great engineering significance to develop a new frame joint structure with strong seismic performance.Based on the test results of the frame joints of a new hospital building in Qingdao,this paper combines the current research status of reinforced concrete frame joints,and proposes two different kinds of joint design schemes for the steel bar to penetrate the new cast-in-place joint and the profile steel through the new cast-in-place joint.Firstly,the finite element simulation of the experimental framework joints in the existing literature is carried out,and the finite element calculation results are compared with the experimental results.It is found that there is a certain acceptable error between them,which indicates that the seismic analysis model of reinforced concrete frame joints established by the finite element program is reasonable and feasible.The finite element simulation analysis of the seismic performance of two new cast-in-place joints is carried out,and the conclusions are as follows:(1)The hysteretic curves of new cast-in-place joints penetrated by steel bars and the profiled steels are full and of good seismic performance.the ultimate bearing capacity and energy dissipation capacity of the latter one is higher than that of the el bars,and it comes with a larger initial stiffness and overall stiffness,but its stiffness degrades faster and the deformation capacity is slightly weaker.(2)With the increase of the mass defect rate,the bearing capacity of the joint decreases gradually;and after the defect rate reaches 10%,the bearing capacity of the joint decreases rapidly,and the bump appears in the skeleton curve which accelerates the stiffness degradation of the joint.With the increase of defect rate,the phenomenon of stiffness degradation becomes more and more serious,the equivalent viscous damping coefficient of joints decreases gradually,and the deformation ability decreases.The existence of internal quality defects has certain damage to the seismic performance of the joints.The greater the defect rate,the worse the seismic performance.(3)the seismic performance of the frame joints can be improved by increasing the reinforcement ratio.With the increase of it,the hysteresis curve is more full,the bearing capacity increases,and the peak value of the skeleton curve increases.The stiffness of the joint increases overall,but which impose no significant effect on the stiffness degradation;the viscous damping coefficient increases gradually with the reinforcement ratio;the yield displacement of the joint increases,and the ultimate displacement has no obvious change,so the displacement ductility coefficient is reduced.Therefore,the design of the reinforcement ratio should be comprehensively considered to make the joints play its role full.