Experimental Research On Seismic Performance Of Sidewall Joints In Partially Prefabricated Subway Station

As a representative of urban rail transit,the subway has the advantages of environmentally friendly,convenient,and efficient,which can effectively alleviate the problem of urban traffic congestion and reduce the occurrence of traffic accidents.With the development of economy,the process of urbanization has accelerated significantly,and the number of subway constructions in cities across the country is increasing obviously.Engineers are exploring more efficient and high-quality methods of subway to meet development needs.The subway facilities are mainly composed of two parts: the tubular passage and the subway station.The subway passage is constructed by shield machine,of which the technology is relatively mature.Subway stations can be divided into two types: underground stations and above-ground stations.At present,underground stations are basically made of open-cut foundation pits and cast-in-situ reinforced concrete.This construction method brings the disadvantages of long time-consuming,complex on-site procedures,and high pollution.Under the trend of the construction industry,domestic engineers began to design underground stations with the theory of prefabricated concrete structures.Prefabricated concrete structures have the advantages of high efficiency and convenience in construction,high degree of industrialization,easy control of the quality of prefabricated components,and low pollution.The development of prefabricated subway station is of great significance to the promotion of urban subway track construction.Domestic prefabricated subway stations started late.Stations are always dominated by fully prefabricated components which are connected by grouting steel sleeves or mortise joints.This paper reviews the literature of the research history and engineering practice of the seismic performance of sidewall joints in prefabricated subway stations by domestic and foreign engineers.Based on the prefabricated subway station project of Nanmen Station of Wuxi Metro Line S1,a new connection method of partially prefabricated sidewall joints of underground stations with U-shaped steel bar connection is proposed.In order to study the seismic performance of new partially prefabricated sidewall joints,this paper divides the single-sided prefabricated sidewall joints into two categories: the prefabricated sidewall roof joint and the prefabricated sidewall floor joint.A total of 8 full-scale sidewall joint specimens were designed for seismic performance tests,including 3 prefabricated sidewall roof joints and 3 prefabricated sidewall floor joints,1 in-situ sidewall roof joint and 1 in-situ sidewall floor joint.Then low-cycle reciprocating load tests were carried out on these joints.Through the seismic performance test,the cracking and failure modes of the specimens were observed and recorded,the load-displacement data of the specimens were obtained,the hysteresis curve,skeleton curve and stiffness degradation curve were drawn..Through the analysis of the data obtained from the test,the seismic performance of the prefabricated sidewall joint of the underground station is judged and summarized.In addition,ABAQUS software is used to conduct finite element modeling analysis on the joint specimens,and the validity of the model is verified by comparing the finite element calculation results with the test results.The simulation hysteresis curve,the simulation skeleton curve and the model stress and strain are compared and analyzed.The difference and reason of the actual measurement results,the axial compression ratio and the strength grade of post-cast concrete are set as parameters for parametric analysis,and the influence of key parameters on the mechanical performance of the semi-precast laminated wall panel joints is summarized.Finally,after seismic tests and finite element simulation results,the seismic performance of single-sided prefabricated joints are summarized,and the following conclusions are drawn:The results showed that:(1)The load-bearing capacity of the single-sided prefabricated sidewall joint meets the requirements of the design under normal use conditions,but under cyclic load,the seismic performance of the sidewall joint is insufficient.The sidewall roof joint specimens have certain ductility and energy dissipation capacity,and the specimens show the characteristics of bending failure;the sidewall floor joints have poor ductility,and the specimens all have brittle shear failure.(2)The load-bearing capacity and energy dissipation capacity of the roof joints of the precast side walls are not as good as those of the cast-in-place roof joints.The U-shaped steel bars in the joint have an earlier bonding failure,and their anchoring capacity is inferior to the longitudinal reinforcement bending anchoring.The connection has a sudden change in stiffness,which affects the bearing capacity of the fabricated bottom joint and the development of cracks.(3)The concrete at the connection part of the U-shaped steel bar at the roof joint of the sidewall is easy to crack.The concrete inside the U-shaped bar is subjected to the radial pressure of the steel bar,which causes the early concrete crushing and spalling to cause bonding failure,which is an important reason affecting the load bearing of the specimen.The ABAQUS finite element simulation shows that:(1)The hysteresis curve and skeleton curve obtained by finite element simulation can reflect the curve characteristics obtained in the test;the stress-strain cloud diagram of the model better reflects the actual stress damage situation of steel and concrete under the test of the sidewall joint specimen.(2)Through the parametric analysis of the roof joint of the precast sidewall,it can be seen that with the increase of the axial compression ratio and the strength of the post-cast concrete,the bearing capacity of the joint will gradually increase,but as the axial compression ratio increases,the deformation and consumption of the specimen Ability declineFinally,the paper sorts out all the research contents and conclusions,and proposes the design optimization method and improvement suggestions of the bending radius of the U-shaped reinforced bar in prefabricated sidewall joints of the underground station,and carries out the existing problems need to be solved and the future research directions.