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Because of the increasing span of arch bridges, ultimate capacity analysis recently becomesmore focused both on design and construction. This paper investigates the static and ultimate behavior ofa long-span steel arch bridge up to failure and evaluates the overall safety of the bridge. The examplebridge is a long-span steel arch bridge with a 50 m-long central span under construction in Shanghai,China. This will be the longest central span of any arch bridge in the world. Ultimate behavior of theexample bridge is investigated using three methods. Comparisons of the accuracy and reliability of thethree methods are given. The effects of material nonlinearity of individual bridge element and distributionpattern of live load and initial lateral deflection of main arch ribs as well as yield stresses of material andchanges of temperature on the ultimate load-carrying capacity of the bridge have been studied. The resultsshow that the distribution patern of live load and yield streses of material have important effects onbridge behavior. The critical load analyses based on the linear buckling method and geometricallynonlinear buckling method considerably overestimate the load-carrying capacity of the bridge. Theultimate load-carrying capacity analysis and overall safety evaluation of a long-span steel arch bridgeshould be based on the geometrically and materially nonlinear buckling method. Finally, the in-planefailure mechanism of long-span steel arch bridges is explained by tracing the spread of plastic zones.