Steel - Concrete Composite Box Girder Stability Study

Two key factors that dominate the load carrying capacity of steel-concrete composite beams are lateral stability and local stability. The research approach in stability of steel-concrete composite beams is summarized. And this dissertation studies the stability of composite beam in the following aspects:1) Based on the theoretical analysis of steel-concrete composite box-beams' lateral buckling, analytical model on the stability of composite box-beams is put forward, and the formula which is used to calculate critical bending moment in negative bending regions is deduced. By comparison with other stability theories and methods, this dissertation indicates the design correction and suggestion about the stability of composite box-beams in negative bending regions.2) The rotation stiffness of the concrete slab and the fastener is brought in to asses the influence of the distortional restraint of the slab and the fastener on the steel top flange. According to above two models, composite beam's lateral buckling is studied in negative moment regions using the energy method, and the formulas which are used to calculate critical bending moment in negative moment regions in the elastic stage are deduced. By comparison with methods in second chapter, this dissertation indicates the design correction and suggestion about the stability of composite beams in negative bending regions.3) The mechanical behavior of steel webs with negative bending will be studied with combined stress loads of flexure, axial pressure and shear. The buckling coefficients for eccentric compression and shear are deduced. And the elastic local buckling coefficient for complicated stress loads is calculated based on interaction equation. The limiting height to thickness ratio was also determined for webs without stiffening ribs in the elastic stage based on the critical buckling load.4) The composite beams are assumed as sandwich beams ,the concrete slab is assumed as the top face sheet ,the steel web are assumed as sandwich beams' core, and the steel flange is assumed as the bottom face sheet. A two-dimensional mechanical model is developed to predict the global and local buckling of steel-concrete composite box-beams, using classical elasticity. The core is assumed to have two deformation modes: antisymmetrical and symmetrical with respect to the core geometric midplane. Characteristics of the two deformation modes and the corresponding buckling behavior are shown and it appears that they are identical when the buckling wavelength is short. Using programming software Matlab to analysis the relationship between the wavelength and buckling stress and the differences between antisymmetrical mode and symmetrical mode...