Spatial Stability Analysis of Butterfly-Shape Arch Bridges Based on Unified Theory

In order to investigate the stability of bridges, based on the unified theory considering the confining action of steel tube, the first- and second-class stabilities of butterfly-shape concrete-filled steel tube arch bridges were analyzed. The first-class stability safety factor was obtained from the calculation of eigenvalue. By considering the effects of the geometry nonlinearity and material nonlinearity on the ultimate bearing capacity, the second-class stability safety factor was gained by the load incremental iteration method. By taking the main bridge on south-central ring district of Taiyuan City as the research object, the spatial stabilities of this bridge at the construction and finished stages were analyzed. The research results show that the stability safety factors obtained by the transformed section method and the composite element method are less than those obtained by the unified theory, so the unified theory can be applied to the stability analysis of concrete-filled steel tube arch bridges. The lateral torsional deformation is the primary buckling form of a butterfly-shape arch bridge, and the structure stability is influenced by the initial imperfection, the distribution of live load, cross wind and so on. The second-class stability safety factor is lower than the first-class stability safety factor.