Study On Numerical Simulation Of Steel-concrete Composite Bridge Considering Interface Discontinuous Deformation

Steel-concerte composite structures consist of steel and concrete parts which are connected by shear connector such as the widely-used headed stud. Through the chemistry bonding, interface friction and mechanical action the two different materials parts are combined as a composite structure system. The mechanical behavior of interface between steel and concrete is complex, and it has important effects on the accurate assessment of steel-concerte composite bridge structures. Base the support from Zhejiang Provincial Natural Science Foundation of "Study on multi-scale analysis method for interface behavior of composite bridge structure", this paper focuses on the key problem of discontinuous deformation of the interface between concrete and steel, and numerical simulation analysis of steel-concrete composite structures considering discontinuous deformation was carried out. The main research contents are as follows:(1) Multiple broken lines mode conesive zone model theory was used to analyze the interface problems in bridge structures, and a zero thickness cohesive element was implemented via the user-defined element subroutine UEL in ABAQUS. Then through a numerical example, discontinuous deformation of the interface, the ultimate load-bearing capacity and the corresponding failure mode were obtained. The feasibility of the proposed method in steel-concerte composite structure simulation analysis is verified.(2) Multiple broken lines mode cohesive zone model was used to simulate the tangential sliding and normal separation of the interfaces. Then a three-dimensional numerical analysis model was established for push-out testing to analyze the load-displacement curves of the push-out test process, interface relative displacement, and interface stress distribution. And the shear capacity and shear stiffness of shear connectors were accurately calculated. The influences of the constraints of the concrete slab base were discussed. Then theoretical derivation was carried out upon the shear stiffness of shear connectors.Thus method to calculate the shear stiffness of shear connectors was determined. (3) The shear connectors are not only subjected to shear forces, but may also subject to tensile force in the loading process. The oncrete crack initiation and propagation of the pull-out process is one of the numerical analysis difficulties. A zero-thickness cohesive interface element based on the enhanced finite element method was introduced. And cohesive zone model was used to describe the crack initiation and propagation of the pull-out process. Then numerical simulation analysis of a pull-out test model was carried out. Results showed load-displacement curves of the structure, pull-out capacity, and crack propagation patterns of the concrete slab. Discontinuous deformation numerical simulation has been realized. Results of this study can be used for the pull-out capacity analysis and the size design of shear connectors of composite structures.(4) On bridge structures, vehicle load is generally perpendicular to the interface of concrete slab and steel girder, and the effect of the interface bond and friction can be more apparent during traffic loading. Thus consideration of bond and friction is needed, especially to accurately calculate the stress state of shear studs during the elastic stage. Mechanical analysis model considering interface bonding and friction was developed for steel-concrete composite bridge structures. A finite element model of a two span composite continuous box-girder was established. Internal force of shear studs, slip distribution and stress distribution of the interface were analyzed. It can carry out the analysis of composite structure without the need to rely on the constitutive laws of shear connectors obtained from push-out tests.(5) Strategy with separated mathematical and physical mesh was adopted, and zero thickness interface element was introduced to simulate the discontinuous deformation of the interface. A three dimensional enhance finite element model considering interface slip was developed. Then finite element models with different boundary conditions considering interface slips were established. Deflections, interface slips and the stresses of control sections were analyzed. Numerical results can agree well with theoretical solutions, and accuracy of the program was verified. With separated mathematical and physical mesh, the size and shape of mathematical elements can be chosen according to the needs of mechanical description of physical elements.In one mathematical element, the physical area can be divided into multiple sub-domains. Each sub-domain can have different materials and different mechanical characteristics. Thus it can greatly reduce the number of mesh elements. The proposed method can obtain high computation efficiency, and can be used for the large scale bridge structures with complicated mechanical behaviors.(6) Taking the Hong Kong-Zhuhai-Macao Bridge as the engineering background, three dimensional finite element model was established, and analysis of large span bridge structures with variable cross-sections was carried out. The three dimensional enhance finite element model considering interface slip was successfully applied to the analysis of actual large scale bridge structures with complicated mechanical behaviors. Thus the feasibility of the proposed method was verified.