Study On Mechanical Performance And Seismic Design Method Of New Type Replaceable Connections In Prefabricated Frame Structures

In order to improve the seismic performance of connection joints in traditional fabricated frame structures,an innovative replaceable connection system,which combines the advantages of bolted connections in convenient construction,post-tensioned(PT)connections in resilient performance,angle steel connections in damage concentration and replaceable after earthquake,is proposed in this thesis.This connection system includes the replaceable beam-column joint and replaceable I-shaped column base joint,each of joint is composed of steel connector,web friction device(WFD),angle steels and PT strands.In this connection system,the self-centering capacity is provided by PT strands,the energy consumption capacity is provided by WFD and angle steels.This connection system fully integrates the bolt connection and pre-compression connection of PT strands,therefore shows the advantages of convenient construction,satisfactory self-centering and feasible replacement.By reasonable design,the joint has excellent seismic performance during earthquake and recoverable performance after earthquake.In this thesis,the seismic performance of the replaceable connection system in fabricated frame structures has been systematically studied by pseudo-static tests,theoretical modeling and numerical analysis.The main contents are as follows:(1)Quasi-static tests were conducted on thirteen groups of twenty-two beam-column joint specimens,and eleven groups of twenty I-shaped column base joint specimens to investigate the hysteretic behavior.Firstly,a joint connection form of setting steel connector and replaceable angle steels between beams and columns,columns and foundations was developed,which could avoid the damage of structural main components under earthquake.At the same time,a construction method of separately tensioning of PT strands in single-span beam and bottom column was proposed,which could avoid the complex construction of high altitude tensioning on site.The feasibility of the above connection form and tensioning method were verified by the pseudo-static test.Then,combined with the test phenomena and results,the damage evolution mechanism of the joint was analyzed.The influence of initial prestress,steel connector flange thickness,form and thickness of angle steel,replacement of angle steel with the same specification and thicker specification after earthquake on seismic performance of beam-column joint were analyzed.The influence of axial compression ratio,angle steel thickness,initial prestress after earthquake,whether to replace angle steel and replace thicker angle steel after earthquake on seismic performance of I-shaped column base joint were analyzed.(2)The mechanical analysis of the end-plate bolted connection interface was carried out.Based on the component method,the rotational stiffness of each component at the interface was considered,and a bilinear moment-rotation model was established.The mechanical analysis of the self-centering interface was carried out.Based on the bilinear elastic model of PT strand,the bilinear elastic-plastic model of angle steel,the rigid-plastic model of the WFD and the bilinear model of the axial pressure,a polyline moment-rotation model of self-centering interface was proposed,which considering the prestress loss of PT strands and the phased mechanical behavior of angle steels.Taking the bending moment of self-centering interface as control moment,and superposing the rotation of the two interface,a theoretical overall moment-rotation model which suitable for replaceable connection joint was proposed,and the calculated results were in good agreement with the test results.(3)Based on the ABAQUS software,the solid three-dimensional finite element(FE)models of specimens were established,and the hysteretic performance was studied.A method to calculate the residual prestress based on the theoretical formula of prestress loss to self-centering interface rotation,then input the target cooling value into the FE model by creating temperature amplitude table was proposed,which realized the accurate simulation of PT prestress,considering prestress loss under hysteretic load.In addition,the method of introducing the initial defect of steel connector through the buckling analysis and the residual stress of steel connector by editing key words was proposed,which realized the accurate simulation of the damage state of steel connector during the secondary loading.The reliability of the FE model was verified by detail co MParing of the simulation results and test results.Subsequently,the parameter expansion analysis for seismic performance influence factors and seismic recovery performance,which were not considered in test,were carried out.The hysteretic performance research of beam-column joints with concrete floor was also carried out.(4)Based on the analysis of experimental and FE analysis results,a performance-based seismic design method of prefabricated frame structures with replaceable connections was proposed.Firstly,the performance-based design objective was put forward,which described as "no damage under minor earthquake,self-centering under moderate earthquake,repairable under major earthquake,and no collapsed under mega earthquake".Then,the seismic design method was established,including the design of joint bearing capacity,PT prestress,steel connector,WFD and replaceable angle steel.Among them,the recommended values were given for the opening moment proportion coefficient,self-centering coefficient and energy consumption coefficient.Moreover,the suggestions were given for the selection of steel connector and angle steel,and the post-earthquake repair measures of the joint.