Finite Element Analysis Of Concrete Structure Cracking In Subway Station

At present, most structure of subway station includes top slab, bottom slab, continuous wall and inner lining wall. Concrete structure will produce crack and leakage phenomenon under the combined effect of all kinds of loads, and the existent of crack and leakage is dangerous to subway regular running, faculty safety working, and will shorten the service life of concrete structure. Level of impermeability and waterproof for concrete structure of subway station, which directly affects construction quality, becomes an important index to evaluate subway station engineering. Because the crossbar proportion of subway station is relatively large, the simplified design method is mostly adopted. This kind of method uses cross section plane structure model to calculate and design structure reinforcement and considers loads are transferred in cross section. The vertical deformation and internal force caused by temperature difference shrinkage is considered by construction measure. Obviously, this method has certain of limitation. To solve such problems discussed above, the following studies have been carried out.A 32 meter long standard segment between induced joints in a composite subway station in Shanghai metro line 7 is studied using finite element method and reinforcement-concrete element, elastic matrix of link reinforcement element in induced joints and element material parameters are given. The main reason of concrete crack and leakage in the composite subway station is obtained through calculating the stress fields under most unfavorable equivalent temperature difference loads. There is shrinkage deformation in subway station concrete structure when temperature drop load is applied to it and eccentric tensioned stress field is produced because of the constrain of the link steel bar at the induced joint and lateral wall. I type crack appears when the first principle stress exceeds tensile strength, and leakage phenomenon appears when crack extends into transfixion crack and crack width exceeds the limited value.Make a spatial finite element model considering surrounding soil constraint and restrain stiffness according to practical situation of subway station to do FEM analysis and obtain stress distribution of subway station under prestressed load and combined load cases. Based on numerical analysis, prestressed concrete technology scheme design is finished including prestress loss and prestress cable quantity estimation, prestressed cable position choice, cable shape and stretching end anchorage location design. The in-suit monitoring datas show that the prestressed technology scheme used in this paper could effectively decrease the tensile stress of concrete and reduce or eliminate the structure crack.In order to get the all kinds of responds information before and after crack appears in subway station, concrete structure nonlinear analysis is making. This paper suggests a kind of concrete constitutive model which could consider compression strength decrease because of cracking, adopting elastic-plastic constitutive theory and considering concrete character after cracking and crushing. This kind of model uses less parameters and could reflect main mechanical properties. Then three-dimensions reinforcement concrete finite element model is studied and a model of three-dimensional embedded combined finite element of reinforced concrete structures has been proposed. This model overcomes the shortages of combined membrane finite element model and the compiled program could consider reinforcement embedded in concrete at any direction. The program should not consider the position of the reinforcement when dividing the concrete elements and the information of reinforcement could produce automatically by concrete element information. Compile a three-dimensional nonlinear finite element analysis program according to nonlinear analysis process. The program could consider combined embedded or membrane finite element model, orthogonal or non-orthogonal crack model and make tracing analysis to crack extending process of subway station concrete structure under temperature drop load.A field test is carried out used a 32 meter long standard segment between induced joints in a composite subway station in Shanghai metro line 7 as the experimental object. The temperature and concrete strain each measuring point is measured since the station construction using strain and temperature sensors embedded in experimental section. Comprise the effect of prestressed scheme, ordinary scheme and fiber concrete scheme by monitoring data and crack situation and then give the corresponding design suggestion to test the project effect of impermeability and waterproof technology. The comprising result of nonlinear analysis t and in-suit monitoring data shows that, the theoretical analysis and monitoring data could match well which verified that the three-dimensional nonlinear finite element analysis program developed in this paper could reflect the structure force mechanism, its changing law and high accuracy calculation result.