Research On Structural Mechanical Characteristics And Seismic Performance Of Prefabricated Underpass Tunnels

In recent years,China has set off a wave of building prefabricated concrete buildings.Compared with cast-in-place concrete structure,assembly technology has significant advantages of high efficiency,economy and environmental protection.Therefore,it is in line with the transformation and upgrading strategy of the construction industry advocated by the government.However,the technology is widely used in housing construction and bridge engineering,and rarely used in underground engineering,especially in open cut large section underground engineering.The research on prefabricated underground structure in China is still in its infancy,and there are many key technologies to be solved.Such us: the selection of prefabricated component type,joint design and joint waterproof,seismic performance of prefabricated structure,etc.In view of this,it is of great practical significance to study the mechanical characteristics of open cut prefabricated underpass tunnel.This paper is based on the fabricated underpass tunnel project of Moziqiao in the first ring road of Chengdu.According to the mechanical characteristics of shallow buried large-span open cut prefabricated underpass tunnel,through the numerical calculation.laboratory test and theoretical analysis are used to do some research.The main achievements and conclusions are as follows:(1)The stress and deformation characteristics of the structure under the load in the operation stage are analyzed,and compared with the whole cast-in-place concrete structure.The most unfavorable section and joint stiffness reduction factor are obtained.(2)By changing the relevant parameters(Number of steel box,Thickness of steel box,Material grade).The bearing capacity difference of the whole structure under different working conditions is further analyzed,and compared with the whole cast-in-place concrete structure.The conclusion of scientific and reasonable structure combination is obtained.(3)The local joint model of "bolt + shear steel box" hybrid connection is established by using numerical simulation software.Calculation of mechanical characteristics of joints under low cycle reciprocating load.By changing the relevant parameters,the stress distribution,failure mode,hysteretic curve and skeleton curve of the joint are analyzed,and compared with the whole cast-in-place joint model.In order to evaluate the seismic performance of the joint used in this project.(4)The indoor experimental study on temperature propagation law of reinforced concrete structure under high temperature environment is carried out.The internal temperature propagation law of reinforced concrete beams subjected to single side fire is proved;The finite element method is used to reproduce the test process and verify the feasibility of the finite element model.Based on the indoor test results,the heat conduction parameters of concrete are optimized,and the transient thermal stress coupling analysis is carried out for the actual prefabricated underpass tunnel,and the most unfavorable section of the structure under fire condition is proposed.