Keywords: concrete-filled steel tube, arch bridge, stability, nonlinearity, load combinations, ANSYS.

Concrete-filled steel tubes (CFST) are widely used in the arch bridges due to their high compressive strength and the efficiency and simplicity in construction. Presently, more than 300 CFST arch bridges have been built in China. Owing to high strength of the materials, the lateral stability is most pronounced in large span CFST arches. The Han River North Bridge (under construction) composed of five continuous spans is the largest CFST arch bridge without lateral braces in the world (160m of the main span). It is also the largest CFST arch bridge with back-to-back shaped ribs which are constituted by the Dumbbell-shaped CFST vertical arches and steel side arches. Such ribs have a better transverse stiffness than the single dumbbell-shaped one does. However, the bridge is located at the region with high typhoons and seismic risks (a 1000Pa of the basic wind pressure and 8 degree of earthquake intensity according to the related national standards of China), its stability will be the key problem. In this paper, a finite element 3-D model of the main span of the Han River North Bridge is developed with the commercial analysis package ANSYS.

Several numerical models were developed to investigate the back-to-back shaped ribs of the Han River North Bridge with ANSYS in reference [1]. Among them, a model using the constraint equation method and the one using double equivalent connecting bar method were thought to be more accurate and suitable for simulating the actual mechanical behaviour of the ribs. However, since the constraint equation is invalid for elements that undergo large deflections, the double equivalent connecting bars model was adopted in this paper.

The stability was investigated through four different methods: the eigenvalue buckling analysis, the geometric nonlinear analysis, the material nonlinear analysis, and the dual-nonlinear analysis considering the nonlinearity of both the material and the geometry. The differences of the predicted results using the four methods were compared and discussed. Some parameters were investigated on the bridge's stability, including the cross-sectional form of the arch ribs, number and locations of the wind braces, loads transferred from the adjacent spans, material strength, action of wind, pretension of the tied bars, and loading combinations, etc. Finally, the important factors among them were outlined.

The following conclusions can be drawn based on the finite element analysis of the Han River North Bridge:

• The material nonlinearity effects the stability of the arches greatly. And the dual-nonlinear buckling analysis considering the nonlinearity of both the material and the geometry is the most accurate method.
• The side ribs improve the transverse stiffness and the stability of the arch ribs commendably.
• In the ultimate state, it is the side arches on which the plastic hinges first appeared and a relatively large plastic region developed. Thus, the stiffness of the side arches should be strengthened at their bases in order that the stability of the arch can be further increased.
• Distributing the wind braces properly can raise the ribs' stability effectively.

1

Yu-yin Wang, Su-mei Zhang, Yue Geng, Gianluca Ranzi; Numerical simulation and research on the Han River North Bridge; ASCCS' 8th International Conference on Steel-Concrete Composite and Hybrid Structures 12nd-15th August 2006, Harbin, China

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