Stability Of Steel-Concrete Composite Curved Box Beams

Steel-concrete composite curved box beams have been widely used in bridge engineering and high rise buildings. Stability is a key factor that dominates the load carrying capacity of steel-concrete composite curved box beams. The design methods to stability of composite beams in the present Chinese codes are basically steel beams, which differ from the stability behaviours of composite beams. For this, the research approach in stability of steel-concrete composite curved box beams is summarized. And this dissertation studies the stability of steel-concrete composite curved box beams in the following aspects:(1) The mechanical behavior of steel-concrete composite curved box beams in common loads will be studied with combined on theoretical analysis of the composite structure, curved beams and steel thin-walled bar buckling theory after considering the cross-sectional warping effects. In an example of simply supported composite curved box girder, analy its cross-sectional moment and double-moment bending moments in the equal ends moment. Combined with restrained torsion box beam theory, find out longitudinal normal stress of steel beam web and the lower cloud point flange.(2) Based on the theoretical analysis of lateral buckling of steel-concrete composite curved box beams, analytical model on the stability of composite curved box beams is put forward. 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 curved box beams in the negative moment are derived.(3) Using the energy variation principe of box girder bottom, thin-walled bar buckling theory and variable axial force elastic foundation strut method to calculate critical bending moment in negative moment regions in the elastic stage. (4) A series of composite curved box beams with different slip stiffness, rations of width and thickness of floor, rations of height and thickness of box beam web, rations of height and length of box beam, section height ratio were studied, analyzing the changes of critical bending moment in negative moment regions of the composite curved box girders and getting the reasonable design parameter values.(5) The same way of Steel beam instability which used in Design of steel structure, we put forward the method of stability of steel-concrete composite straight box beams and curved box beams.