Reliability-based capacity safety factor for G20Mn5 cast steel joints

Cast steel joints have complex geometries and great load-carrying capacity, and hence their resistances are commonly determined through FE simulations. Considering the significant variability in the material mechanical properties (that in fracture strains, in particular) and the model uncertainty inevitably involved in the FE analysis, a large safety factor (gamma R) should be adopted for the FE simulation-based design of cast steel joints. However, the gamma R-values specified by the current design specifications, e.g. the Chinese standard CECS 235: 2008 in which gamma R = 3.0, are deemed to be overly conservative. This paper examined the structural reliability of G20Mn5 cast steel joints to provide a rational gamma R-value for the practical joint design. The above-mentioned uncertainty of the material and geometric properties as well as the model uncertainty related to FE simulations are evaluated, and Monte Carlo simulations were conducted on nine representative joints to obtain the statistical characteristics of cast steel joints' ultimate resistance, allowing for both failure modes of material fracture and instability caused by large-scale yielding. FORM was adopted to calculate the reliability index beta for the assumed gamma R-values and different loading scenarios, and the recommended values for gamma R under target reliability indices are proposed. For snow load-dominant and wind load-dominant load combinations, the recommended gamma R corresponding to beta = 4.2 are 2.29 and 2.16, respectively, and the recommended gamma R corresponding to beta = 3.7 are 2.01 and 1.90, respectively.