Research On Hysteretic Performance Of Concrete Frame Joints

Earthquake and experimental at home and abroad show that frame joints is one of the weak link of the seismic frame structure.Shear deformation of joint core and beam longitudinal reinforcement bond-slip is the key of nonlinear analysis.On the basis of studying the mechanical characteristics of concrete frame joints,the thesis expounds the working mechanism of macroscopic mechanical model,using the beam-column joints unit of elastic-plastic finite element software,concrete frame joints calculation model is established,the author analysis the hysteresis curve of some concrete frame joints under low cycle loading at home and abroad,establishes the calculation model of concrete frame joints.Finally,the author analysis the mian factors that influence the hysteretic behaviors of frame joints,some meaningful conclusions are obtained which can be used to guide the concrete frame joints design.The main completed contents are as follow:(1)On the basis of extensive reading of literature at home and abroad,a brief overview of the research status quo and the working mechanism of concrete frame joints,experiment research and finite element analysis of frame joints at home and abroad are summarized.The thesis puts forward the problems of the hysteretic performance study of frame joints and in the necessity of further research on frame joints.(2)The thesis systematacially illustrates nonlinear analysis theory of frame joints based on macroscopic mechanical model.Introduced detailedly the method to determine the shear stress and strain skeleton curve based on the diagonal compression strut model.Through analysis the effect of the frame joints hysteresis characteristics under the low reversed cyclic loading by two major factors that reinforcement bond slip and shear deformation of joint core,Finite element model of concrete frame joints is established based on software OpenSEES,the thesis implements the nonlinear numerical simulation of concrete frame joints of Chongqing university FU Jianping,The experiment results are in good agreement with computed result,to verify the applicability and reliability of the finite element model.(3)Based on OpenSEES software,the thesis established the finite element model of prestressed concrete frame joints which considering the non-prestressed reinforcement bond slip and shear deformation of joint core,and carries out the nonlinear numerical simulation of prestressed concrete frame joints of Park?TANG Jiuru and CHEN Yong.Simulation results are in good agreement with experiment results,and provides a new way for seismic analysis of prestressed concrete frame joints.(4)through analysis the influence of concrete frame joints of the four main factors,namely,axial compression ratio,shear compression ratio,stirrup characteristic value and prestress degree,the thesis designed 26 concrete frame joints and 5 prestressed concrete frame joints,from the ultimate bearing capacity,displacement ductility and energy dissipation ability three aspects has carried on the finite element analysis of the hysteretic performance.Analysis results show that in order to make concrete frame joints has enough ductility,suggested the stirrup characteristic of concrete frame joints should not be more than the calculated value of seismic shear bearing capacity calculation formula of code,at the same time,suggest cut ratio should not be more than 0.3,When the axial compression ratio exceeds 0.5,the beneficial effect on the joints shear is reduced;In order to make the prestressed concrete frame node has enough ductility,the author recommended the prestressed degree shoulds not be more than 0.75.