A Modified FOSM Method for the Reliability Assessment of Cold-Formed Steel Members

Resumo

The FOSM (First Order Second Moment) method is a structural reliability analysis technique that estimates the probability of failure based on the first two statistical moments (mean and variance) of the variables involved. Structural reliability assessments are often conducted using the FOSM method due to its simplicity and the absence of advanced computational requirements. Unlike more complex approaches—such as the First Order Reliability Method (FORM), which involves variable transformations and iterative procedures, or Monte Carlo Simulation (MCS), whose accuracy depends on a large number of simulations—FOSM provides a straightforward and practical framework, suitable for the calibration of design codes. However, this simplification compromises the accuracy of FOSM. This paper proposes a modified version of the FOSM method (denoted FOSMₘ), which incorporates adjustment functions to better approximate the results of MCS in the reliability analysis of cold-formed steel members. The FOSMₘ method showed excellent agreement with MCS results for load combinations of the type D (dead load) + L (live load), with L/D ratios ranging from 1 to 10. Moreover, FOSMₘ proved to be effective when applied to typical ranges of load factors used in the design of structural members. The proposed methodology retains the simplicity of FOSM while significantly improving its accuracy, offering a robust and accessible alternative for structural reliability assessments.