Static And Dynamic Performance Of Steel-concrete Composite Box-beam And Frame Structure

Steel-concrete composite box-beams have been widely used in bridge engineering and high rise buildings. At present, there were many open questions on the dynamic and static performance considering the shear lag effect of steel-concrete composite box girder, such as the experimental study and theoretical analysis on the dynamic and static performance considering the shear lag effect of steel-concrete composite box girder concentrated on I-type steel-concrete composite girder, the computing method about distortional buckling critical bending moment of the steel-concrete composite box girder was too complex, dynamic response analysis methods considering the shear lag effect of steel-concrete composite box girder had not been reported, bending moment-curvature restoring force calculation models were mostly based on component, and the elastoplastic seismic response time history analysis program of composite structures were mostly based on layer model, and so on. The theoretical research laged behind the engineering practice seriously. By developing the experimental study and theoretical analysis on the dynamic and static performance considering the shear lag effect of composite box-girders, the composite box-girders can be used popularization and application in bridge engineering and super high rise building. The main research works completed in this paper are as follows:(1) Based on the consideration of longitudinal warp caused by shear lag effects on concrete slabs and bottom plates of steel beams, shear deformation of steel beams and interface slip between steel beams and concrete slabs, the governing differential equations and boundary conditions of the steel-concrete composite box beams under lateral loading was derived using energy-variational method. According to the virtual work principle, the unit stiffness matrix and equivalent nodal force vector of the composite beam were established in consideration of the slip effect, shear lag effect and shear deformation. The closed-form solutions and beam finite element method calculate results of stress, deflection and slip of box beams under lateral loading were obtained, and the comparison of the analytical results and the experimental results for steel-concrete composite box beams under concentrated loading or uniform loading verifies the validity of the closed-form solution. The parameter analysis of shear lag coefficient of concrete roof and steel baseplate had been proceeded using calculation method of this paper. The relatively accurate shear lag coefficient of concrete roof and steel baseplate was put forward.(2) Lateral bending buckling and lateral flexural-torsional buckling are both important buckling modes for steel-concrete composite beams in the negative moment region, and only the lateral bending buckling is considered in the existing computing method, so there is some limitations. Based on the rotational restraint stiffness and lateral restraint stiffness calculation formulas provided by the steel beam web plate to the lower cloud point flange and the thin-walled bar buckling theory, the calculation formulas of the lateral bending and lateral flexural-torsional buckling moment of the steel-concrete composite beams in the negative moment are derived. The example analysis shows that the existing computing methods all have some theory shortcomings, and the computing method of this paper is more reasonable. At the same time, the calculation results of this paper is more concise than the calculation formulas of the same type, easy to be applied, so it is suitable for engineering application.(3) Based on Hamilton principle, the governing differential equations and the corresponding boundary conditions of steel-concrete composite box girder with consideration for the shear lag effect meeting self equilibrated stress, shear deformation, slip, as well as rotational inertia were induced. Therefore, natural frequency equations were obtained for the boundary types, such as simple support, cantilever, continuous girder and fixed support at two ends. The ANSYS finite element solutions were compared with the analytical solutions by calculation examples and the validity of the proposed approach was verified, which also shows that the correctness of longitudinal warping displacement functions is reasonable. The proposed approach provided theoretical basis for further research of free vibration characteristics of steel-concrete composite box-girder. The vibration differential equations were solved using central difference method, and the dynamic response of steel-concrete composite box girder under arbitrary loading was obtained. The finite element computed results was compared with the difference computed results and the validity of the difference method was verified.(4) Four specimens of steel-concrete composite box-girders with different shear connection degree and height-width ratio of web plate under cyclic points concentrated loads were experimentally studied. The failure mode, load-deflection hysteretic curves, ductility, energy-dissipating capacity, rigidity degeneration etc were deeply studied. The shear connection degree and height-width ratio are considered as the experimenters parameters of the seismic performance. The influence of shear connection degree on bending rigidity of steel-concrete composite box-girders was considered by power function interpolation method. The positive and reverse elastic stiffness of bending moment-curvature considering the interface slip was put forward, and also the section yield moment. The trilinear skeleton model of bending moment-curvature was proposed, and the computing method of the model is very simple, which is convenient to be used in engineering. Best on the test data and theoretical analysis, The positive and reverse stiffness degradation rule was obtained, the trilinear bending moment-curvature restoring force calculation model was further proposed, and the computing method of the model is also very simple, which is convenient to hand computation.(5) The trilinear bending moment-curvature restoring force calculation model proposed in the text was programmed, the variable stiffness rod element stiffness matrix suiting elastoplastic seismic analysis on steel-concrete composite box-girders was proposed. The conversion diagram suit on numerical calculation of composite structures was programmed. Based on the conversion diagram and the variable stiffness rod element stiffness matrix, the elastoplastic seismic response time history analysis program of composite structures was programmed using Wilson-θ incremental numerical calculation method. Some steel-concrete composite frame structure specimens with different design parameter were calculated using the elastoplastic seismic response time history analysis program. The reasonable anti-seismicdesign suggestions were proposed.