Research On The Mechanical Behavior Of Components And Joints In A Novel Composite Prefabricated Subway Station Under Open-cut Construction

In the process of achieving the strategic objectives of "carbon peaking" and "carbon neutrality" and in the context of the rapid development of urban rail transit in China,the prefabricated subway station structure has attracted extensive attention for its advantages of reducing consumption and carbon emissions.In this study,a new type structure system of composite prefabricated subway station under open-cut construction is proposed by our research team based on an actual engineering case.The novel structure system has the advantages of favorable integrity and water resistance,and relatively high on-site construction efficiency.It can be applied to the construction of prefabricated subway stations with open-cut construction method under the condition of foundation pit internal support in water rich soft soil regions.To promote the application of the proposed station structure in subway engineering,the mechanical properties and design methods of the composite roof slabs,composite sidewalls,joints between sidewalls and roof slabs,and joints between sidewalls and floors in the station structure were systematically studied by combining experimental research,numerical simulation and theoretical analysis,and the design method and process of the overall structure of the subway station were proposed.The main research work and conclusions are as follows:(1)The mechanical properties of prestressed concrete composite roof slab with concrete rib in the station structure are studied.4 full-scale composite slab specimens were designed and manufactured,and they were divided into one-stage loaded and secondary loaded composite slab specimens respectively through different monotonic static loading schemes.The strain of reinforcement and concrete,stiffness,crack development and flexural capacity of normal section of the one-stage loaded and secondary loaded composite slabs during the loading process were compared and analyzed.Based on the experimental study,the flexural capacity of the composite roof slab was numerically analyzed.The test and numerical analysis results show that the overall mechanical performance of the prestressed concrete ribbed composite slab is satisfactory,and there is no slip between the post-pouring concrete and the precast member during the testing process.In addition,the ultimate bending capacity of the composite slabs under two-stage loading is higher than that of the composite slabs under one-stage loading.However,the cracking moment,yield bending moment,and corresponding bending moment when the mid-span displacement reached the design limits of the secondary loaded specimens are lower than those of the one-stage loaded specimens.A theoretical calculation method suitable for the design of flexural bearing capacity of prestressed concrete composite roof slab with concrete rib is proposed.The comparison with the numerical simulation results shows that the calculation results are more accurate.(2)The mechanical behavior of the common position of the composite sidewall in the proposed station structure is studied.The eccentric compression test of a composite sidewall specimen and a monolithic cast-in-situ sidewall comparison specimen was conducted to investigate the eccentric compression behavior of one-sided partially prefabricated sidewall members.On this basis,the theoretical calculation formula applicable to the design of eccentric load bearing capacity of one-sided partially prefabricated sidewall members is proposed.The research results show that the deformation law of the composite sidewall section is consistent with that of the cast-in-place sidewall section under the compression and bending conditions,and both conform to the "average strain plane section assumption".The relevant design formulas about compression bearing capacity of normal cross section of eccentric compressive member in the current Chinese code GB50010-2010 can be extended to the calculation of the eccentric compression bearing capacity of composite sidewall members.The calculated results are in favorable agreement with the test results.(3)The mechanical behavior of the opening position of the composite sidewalls in the proposed station structure is studied.In this study,an entrance frame system suitable for the developed subway station structure and convenient for installation is proposed.This entrance frame is applied to the large opening position of the sidewall at the connection between the main body of the subway station and the entrance passage,and is used to strengthen the sidewall with openings.A 1/2 scale substructure specimen including the proposed entrance frame,sidewalls and roof slab was designed and manufactured.The mechanical behavior of the composite sidewall at the opening was studied by monotonic loading static test.Based on the experimental study,the numerical simulation analysis is carried out,and the preliminary design suggestions for the entrance frame are given.(4)The seismic performance of the joint between the composite roof slab and composite sidewall in the proposed station structure system is studied.3 full-size prefabricated joint specimens with different overlapping structures of longitudinal bars were designed and manufactured.Quasi-static tests and finite element analysis on 3 full-scale joint specimens were conducted.The failure mode,bearing capacity,deformation capacity,energy dissipation capacity of joint specimens under monotonic cyclic load were studied.In addition,the degradation law of bond stress between tensile longitudinal reinforcement and concrete in the joint area was revealed,and the deformation composition and failure mechanism of the joint were analyzed.On this basis,a strut and tie model was proposed to determine the minimum bending radius of U-shaped bars and 90-degree hooked bars in the developed joint between the roof slab and sidewall.(5)The seismic behavior of the joint between the sidewall and station floor in the station structure is studied.To investigate the seismic behavior of the assembly joint,3 full-scale precast sidewall and floor joint specimens with different positions of the lap connection,and one full-scale cast-in-place concrete joint specimen for comparison were designed and manufactured.The critical seismic performance measures associated with the joints,such as failure mode,bearing capacity,hysteretic characteristics,and mechanical performance of Ushaped bars overlapping connection were compared and analyzed based on the quasi-static test.Combined with the anchorage performance test of U-shaped bars,a theoretical calculation method for the reasonable lap length of U-shaped bars of the assembly joint was proposed.Based on the experimental study,the seismic behavior of the joint specimens between the sidewall and station floor was numerically analyzed.The effects of the design parameters such as the overlap length of the U-shaped bars,the stirrup ratio of the sidewall,the strength of the laminated layer concrete,and the axial compression ratio on the seismic performance of the assembly joint were systematically studied.Suggestions are put forward for the optimal design of the prefabricated sidewall and station floor joint.(6)In this study,the bending and shear capacity of the roof slab and sidewall joints,the bending and shear capacity of the sidewall and station floor joints,the shear capacity of the vertical and horizontal interfaces of the composite sidewalls and the shear capacity of the horizontal interface of the composite slabs in the composite prefabricated subway station are studied.Combined with the results of test and finite element analysis,the design method of joints and components in the developed station structure is further proposed,and based on this,the design method and process of the overall structure of the subway station are constructed.It can promote the further promotion of the new type structure system of composite prefabricated subway station.