This paper is to introduce a new approach to analyze the ultimate load bearing capacity of arch bridges. Based on the nonlinear stress strain relationships of concrete and reinforcement, a nonlinear finite element program is proposed. The following factors are considered in this program: the bond slip effect between concrete and reinforcement, the non-homogeneity of reinforcement stress after concrete cracks, the material nonlinearity as well as the second order effect. Also, M-Φ and N-ε curves of each section under different load grades are calculated in pure numerical method from the beginning of adding loads to the failure of the bridge. Therefore, the accurate stiffness EI and EA together with their distribution patterns can be obtained from these curves. As the result of comparison, the theoretical P - Δ curves are in good agreements with the measured ones. This paper provides an accurate and practical method for the analysis of the ultimate load bearing capacity, maintenance, reinforcing, and studies on seismic behaviour of arch bridges.
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