Finite-Element Analysis For Nonlinear Stabilities Of Concrete-Filled Steel Tubular Arch Bridges

Owing to many advantages such as large-scaling ability, high load capacities, good fireproofing and earthquake resisting behavior and convenience for construction, concrete-filled steel tubular (CFST) arches have been more and more widely used in practical constructions. The fundamental failure modes of CFST arches are loss of stability and loss of material strength, and loss of stability comprises losses of in-plane stability and out-of-plane stability. For long-span CFST arch bridges, when reaching in-plane or out-of-plane buckling state the material in general enters the elastic-plastic deformation range and the resulting displacements are usually large. Therefore the in-plane or out-of-plane stability problem is that of double nonlinearity including material and geometric nonlinearity.In this paper the finite element method is used for analysis of the in-plane and out-of-plane stability problems for CFST arch bridges, considering the material and geometric nonlinearity. A refined finite-element model for division of arch ribs is first established, in which the four-node flat shell element is employed for the outer steel tubes, the eight-node solid element for the inner concrete and set two-node link (bar) elements for the reinforcing steel bars. Then using the total Lagrange (T.L) method the tangent stiffness matrixes for the eight-node solid element and the four-node shell element are derived. The resulting nonlinear algebraic equation set is solved using the step-by-step Newton-Raphson iteration. Using the current finite element model the in-plane ultimate load-capacity analysis for a CFST arch bridge experiment model is first performed. The obtained results are compared with those of the experiment and those using the single beam-element model. This demonstrates the effectiveness of the present analysis method. Then the out-of-plane stability of the above arch model is analyzed. The first four buckling mode shapes and the ultimate load-capacity due to the out-of-plane buckling under the action of different out-of-plane disturbing loads are found. Finally the in-plane ultimate load-capacity and out-of-plane stability for a practical example-Yiwu HuanYuan CFST arch bridge are analyzed. The obtained in-plane deflection is compared with the corresponding site-test result. The buckling mode shapes and the sequence of in-plane and out-of-plane buckling for this arch bridge are in detail discussed. Through the above analysis and discussion it is seen that the present finite-element model not only can be used for simulation of CFST arch ribs with any cross-sectional shapes and any boundary conditions under any loading, but also more accurately find the in-plane and out-of-plane buckling loads compared with the method using a single kind of beam elements.