| Large span catenary arch bridge is becoming more and more popular in recent years. But with the span grows larger and larger, structural stability will be a crucial problem during design and construction process. Due to uncertain factors during construction stage, initial geometrical imperfections can not be avoided.Spline functions can be used to approach arbitrary continuous curves with high accuracy. Here, spline functions are used to approach initial geometrical imperfections with different types and different magnitudes, as well as building spline finite element of 3-D curve beam.In this paper the Spline functions method is used analysis of the in-plane and out-of-plane stability problems for Catenary concrete-filled steel tubular arch bridges, considering the material and geometric nonlinearity. With the cubic B spline functions treated as displacement functions, building stability control equations to solve both out-plane and in-plane stability problems. Deducing inflexibility matrixes and load vectors by spline functions. Initial geometrical imperfections are taken into account in the equations and programs. Geometric nonlinearity adopt total lagrangian formulation, deduce double nonlinearity stability control equations of initial geometrical imperfections catenary arch, with corresponding programs complied in Matlab. The results show that :(1)the types of initial geometry imperfections which are familiar to the first order buckling mode will result in buckling earlier.(2)The infection to stability by initial geometrical imperfections is distinctness. So it's necessary to control initial geometrical imperfection range during construction stage. (3)The value of the stability factor only decreased a little when taking into account geometrical nonlinearity. But when the geometrical nonlinearity and material nonlinearity are all considered, the value of the stability factor decreased a lot, so considered material nonlinearity is important.
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