Seismic Behavior Of Modular Prefabricated Steel Reinforced Concrete Column-steel Beam Composite Joints

Prefabricated steel-concrete composite structures are gaining more and more attention and application in the process of building industrialization,and have become the focus of research by experts and scholars at home and abroad.Beam-column joints are the core parts of the assembled steel-concrete composite structure system.It is necessary to study its mechanical properties and practical design methods.In this paper,the seismic behavior of a new modular prefabricated steel reinforced concrete column-steel beam composite joint(abbreviated as modular composite joints,MPCJ)is studied.The main research work and achievements are as follows:(1)Quasi-static tests were carried out on three external joints and three internal joints.The test variables include beam end connection mode(bolt-welded hybrid connection,welding connection,and bolt connection),beam-column stiffness ratio,and beam-column flexural capacity ratio.The influence of different parameters on seismic performance of joint specimens is studied.The seismic characteristics of the joints,such as performance degradation,ductile deformation and energy dissipation,are analyzed.The results show that the load-displacement curves of the joint specimens are full,the energy dissipation capacity is strong,the stiffness and bearing capacity degradation performance is stable,and the modular composite joint has good bearing capacity and seismic performance.(2)On the basis of the experimental results,the three-line restoring force model considering stiffness degradation and the nonlinear seismic damage model based on the two-parameter combination of deformation and cumulative energy dissipation are established by means of dimensionless processing and numerical regression analysis,respectively,and the validity of the experimental results is verified.The results show that the proposed restoring force model can fully reflect the degradation law of loading,unloading and reloading stiffness of skeleton curve,and provide theoretical basis and reference for elastoplastic time history analysis of modular composite structures.The established seismic damage model can correctly reflect the damage situation of modular composite joints under earthquake and make an objectiveevaluation.It lays a foundation for seismic design,post-earthquake damage assessment,and repair and reinforcement of modular composite structures.(3)The refined finite element models corresponding to the test joints model were established respectively through ABAQUS.The feasibility and reliability of the finite element model are verified,and the main stress distribution of the joint specimens is clarified.On this basis,the effects of the axial compression ratio,the concrete strength in the joint core area,the width-thickness ratio of the square steel tube in the joint module,column end connection bolt margin and aperture,the joint cover plate thickness on the seismic performance of the joint are systematically analyzed.The results show that when the axial compression ratio is less than 0.45,the bearing capacity and deformation performance of specimens increase with the increase of the axial compression ratio,but the increase is less than 5%.The bearing capacity,corrosion resistance,and fire resistance of the joint specimens can be effectively improved by increasing the concrete strength in the joint core area.The width-thickness ratio of square steel tube in the joint module has obvious influence on the peak load,the shear deformation,and overall stability of the square steel tube(joint module).Reducing the column end connection bolt margin is beneficial to improve the deformation performance of joint module,and increasing the bolt aperture is beneficial to the rapid assembly of field components,but the influence of both on the bearing capacity of joint specimens can be neglected.Increasing the joint cover thickness can effectively increase the joint bearing capacity,but increase the shear deformation inside the joint module.(4)In order to facilitate the popularization and application of this new type of joint in practical engineering,the experimental research,theoretical analysis and related research results at home and abroad are summarized,the stress and shear mechanism of the joints are expounded,and the calculation formula of the shear bearing capacity of joints are deduced.The results show that horizontal shear resistance of joints is mainly composed of ‘steel plate shear wall' mechanism and‘T-shaped steel frame' mechanism.According to the deduced formula,the theoretical value are in good agreement with the experimental value.The correctness andreliability of the calculation method of shear bearing capacity of the joint core area are verified.Finally,some suggestions on the construction of modular composite joints are given.