Concrete Filled Steel Tubular Symmetrical Bending Pressure Arch Branch Point Instability Problem

Arch bridge is the main bridge type in China and the building of Concrete Filled Steel Tube (CFST) arch bridge is in the ascendant. However the research of stability of arch is not systemic and in-depth and the research of power capability of CFST arch bridge is just to begin. In this paper, the model tests of CFST arch under symmetry-multi concentrated loads have been carried out and the results are analyzed with the comparison of the Steel Tube (ST) arch experiment. The stability of press-bending arch is discussed thoroughly in this paper. The phenomenon, characteristic and judge criterion of bifurcate bucking for the arch that is under symmetry-multi concentrated loads are introduced. The probability of bifurcate bucking for press-bending arch is emphasized. It indicates that the method of limit-point analysis does not take the place of bifurcate bucking analysis for press-bending arch. From the experiments, it reveals that the CFST bridge has good load carrying capacity and elastic-plastic behavior. With the comparison of the Steel Tube (ST) Arch, it will improve the ultimate strength and the capacity of anti-deformation by filling the concrete in steel tube. The design formula for calculating the linear-bucking ultimate strength of arch in some country codes is concluded and the model arches are calculated according to them. The results show that the formula which is based on the theory of pure-press arch bucking are not adapt to the bucking analysis of press-bending arch. The finite element method for bifurcation bucking of press-bending arch by considering the pre-bucking deformation is also carried out. The result shows that it will be more approaching the authenticity than the method of linear-bucking.