| Concrete-filled steel tubular (CFST) is regarded as the new-type combined material, and has very mechanics performance when pressed. The steel tube itself can be used as formwork and supporting frame during construction. A lot of interim facility can be saved. And its indexes, such as fire-resistant, dynamical property, stability, are better than ordinary reinforced concrete, has been developed rapidly in bridge construction. After Wangcang East-river Bridges was build in 1990 in Sichuan Province, the applications of concrete-filled steel tubular arch bridges have been made more and more in recent years. But, as a new-type structure of bridge, the theoretical researches of CFST arch bridges gets oppositely behind the engineering practice, the study on design theories are incomplete, Structural reliability rating is some of the urgent problems need to be solved in the engineering field.The idea of designing and evaluating structure according to the reliability theory is a great improvement for structure engineering in the past decades, but the application is only limited to component level, otherwise most of the structures are structure systems which are composed of many components. Recently, how to solve the system reliability of large structures availably is a hotspot.Based on the CFST arch bridge of Shenyang hun-river Changqing Bridge, a whole bridge model is established to make a numerical simulation of the construction courses of the composite ridge. Main works which have been done in this paper are listed as follow:1) Activate-kill elements of ANSYS software are applied to simulate the different construction stages of this CFST arch bridge by the ullimate bearing capacity design method. To get the final computational staic force analysis results of this CFST arch bridge, programming techniques of ANSYS was taken into account to add and compositor the value of differenet construction stages, and so on. And then attain final computational results which offers data for static force and the evidence for the judgement of the main failure model of invalidation in the reliability computation.2) By study and analysis of language, ANSYS Parameter Design Language (APDL), which provided by ANSYS FEA software. The second development approach of ANSYS software was introduced to calculate the structural system reliability of complex large-scale structures.It is well-known, the failure mode in the structural system reliability of very large structure is unknown by the implicit nature of the limit-state function. Approximation methods such as the response surface method (RSM), which has been developed in the ANSYS FEA software, are widely used to alleviate the computational burden of engineering analyses. A mixed method for calculating reliability index is presented through combination of the advantages of the response method (RSM), ANSYS parameter design language (APDL), first order reliability method (FORM), which can calculate the reliability of complex large-scale structures of which the limit state functions are not known explicitly. The applicability, efficiency and accuracy of the mixed method are verified by numerical examples.3) The mixed method which combining of the advantages of the response method (RSM), ANSYS parameter design language (APDL), first order reliability method (FORM) is applied to calculate the reliability index of CFST arch bridge. For discussing effect of the error brought by closure in vault, this paper assumes the error of closure is -0.3m (account for 0.84 percent of the rise) , and calculates the deadweight's effect to vault, the result indicates that it is indistinctively. However, the data of the reliability index descends notable (it decend from 3.04 to 2.44) .
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