Research On Structural Optimization And Shear Performance Of Steel Reinforced Concrete Upturned Beam In Metro Station

In order to leave enough headroom for the installation of integrated pipelines in the equipment area,the longitudinal beams of the top slab are usually set as upturned beam in subway stations.However,the upturning structure of the roof longitudinal beam not only increases the construction difficulty,construction period and project cost,but also affects the backfill quality of the station foundation pit,and even causes secondary diseases such as uneven settlement of the subgrade above the station and pavement cracking.This problem can be effectively solved by adding steel inside the reinforced concrete upturned beam to form the steel reinforced concrete upturned beam.With the advantages of high bearing capacity,large stiffness,small section size,good seismic performance and strong crack resistance,the steel reinforced concrete upturned beam can meet the requirements of underground structure for large span and effectively reduce the height of the upturned beam,as well as improve the bearing performance and seepage resistance of the top slab of the subway station structure.However,the stress state of upturned beam is different from that of underturned beam,and the existing calculation theory and construction regulations of steel reinforced concrete upturned beam is not perfect,especially the shear performance is not clear yet.Therefore,it is necessary and urgent to carry out in-depth research on the structural optimization and shear performance of steel reinforced concrete upturned beam.Based on the previous research on the spatial effect of the subway structure roof and the bending resistance of the steel reinforced concrete upturned beam,this paper deepens the design of the steel reinforced concrete upturned beam structure through BIM technology,and then use ABAQUS finite element software to optimize the steel reinforced concrete upturned beam.The numerical simulation is carried out to study the influence of the main parameters on the shear capacity of the steel reinforced concrete upturned beam,and the calculation method of the shear capacity of the steel reinforced concrete upturned beam is proposed.The main contents and conclusions of this paper are as follows :(1)Combined with the characteristics and advantages of BIM technology,the 3D visualization of Revit software was used to deepen the design of steel bar arrangement and concrete pouring of steel reinforced concrete composite structure joints,and Navisworks software was used to check the collision and 4D construction simulation.By optimizing the steel bar arrangement and concrete pouring of complex joints of steel reinforced concrete composite structure,the problems of steel bar collision and concrete pouring quality of joints in the actual construction process were solved,which greatly improved the quality and efficiency of structural design and facilitated the project construction handover and on-site construction.(2)Based on ABAQUS software,six groups of finite element models of steel reinforced concrete upturned beam and steel reinforced concrete downturned beam were established.By comparing and analyzing the failure mode,stress distribution,load deflection curve and ultimate load of upturned beam and downturned beam,the shear performance difference between steel reinforced concrete upturned upturned beam and downturned beam was analyzed.The comparative analysis results show that the shear performance of the steel reinforced concrete upturned beam is lower than that of the downturned beam,and the ratio of the two increases with the increase of the shear span ratio.The finite element simulation results are in line with the research conclusions of Tsinghua University.The weakening of the shear strength of the beam should be considered in the structural design.On this basis,24 groups of steel reinforced concrete upturned beams with different structural forms were designed and established.The finite element method was used to analyze the parameters.The influence of shear span ratio,concrete strength grade,steel strength,steel ratio and stirrup ratio on the shear capacity of inclined section was studied.The results of parameter analysis show that the shear span ratio and concrete strength grade have great influence on the shear capacity of steel reinforced concrete upturned beam.Specifically,the shear capacity is negatively and positively correlated with the shear span ratio and concrete strength grade,respectively,while the steel strength,steel ratio and stirrup ratio have little effect on the shear capacity.(3)According to the superposition method and the current code of our country,the finite element analysis results were regressed and fitted,and the calculation formula of shear bearing capacity of steel reinforced concrete upturned beam in subway station was put forward.The test results showed that the calculated values of the formula in this paper were in good agreement with the finite element calculated values and are safe,which can be used to guide the engineering design.