Effect Of Dual Nonlinearity On The In-plane Stability Of Long-span Arch Bridges

The stability of long-span concrete filled steel tubular(CFST)arch bridges play an important role in bridge design.Many nonlinear behaviors including geometrical nonlinearity,creep nonlinearity will affect the stability.In addition,debonding phenomenon will also decrease the rigidity of arch bridges.Those effects would increase long-term displacements,ultimately leading to lower buckling loads.Those behaviors will be taken into account in this study,utilizing analytical method and FEM method,to investigate the effects on the stability of long-span CFST arch bridges.Main research work is listed as following.(1)In order to investigate vertical displacements of arch bridges,this study introduces an analytical method from former research which is testified by finite element models in ANSYS.Nonlinear geometry is considered in this method and its influence on vertical displacements is explored.(2)A calculation method of vertical displacements considering creep nonlinearity is studied.Based on Age-Adjusted Effective Modulus(AAEM)method,the modulus of core concrete under early-aged loading conditions can be calculated.Combining with the effective modulus,the analytical method introduced before can be used to analyze the deformation of arch bridges.Based on this,how the equivalent stiffness reduction affects the stability of CFST arch bridges will be investigated.(3)The debonding behavior has also been studied in the term of its influence on long-term stiffness of composite cross section.The comparation between the results of shell-solid FEM models and experiments are processed to verify the rationality of FEM method.Parametric analysis has been done to investigate the effect of creep and debonding on the flexural capacity of arch bridges.According to the outcomes,long-term stiffness can be calculated by a fitting formula.(4)This study proposes an analytical method to analyze the vertical displacement of arch bridges which can consider geometrical nonlinearity,creep nonlinearity and debonding phenomenon.This study demonstrates that the combined effect of geometrical nonlinearity and material nonlinearity is much more obvious than any single behavior.Therefore,any single effect should not be neglected in the analysis of stability problems.(5)Equivalent vertical displacement is defined as vertical deflection calculated by equivalent long-term stiffness.Imposing equivalent vertical displacement as an initial imperfection on finite element model,the stability of long-span CFST arch bridge can be analyzed.It could be concluded that equivalent vertical displacements should be considered reasonably when calculating buckling loads of long-span CFST arch bridges.