Reliability assessment of cold-formed steel beams by the FORM method

Abstract

This article presents a procedure for the reliability assessment of cold-formed steel beams based on the Direct Strength Method (DSM) and the Effective Section Method (ESM). Using a comprehensive database, a statistical analysis of the test results was performed to determine the statistical properties of the professional factor random variable. The statistical parameters related to material strength, geometric properties and load effects were obtained from established references for reliability analysis. Safety levels compatible with the North American and the Brazilian codes relating to structural design of cold-formed steel members have been established. The first-order reliability method (FORM) was used to calculate resistance factors φ for usual nominal live-dead ratios. The results of the reliability analysis showed that the DSM and ESM design methods have similar levels of reliability. The same resistance factor as the DSM can be used for the ESM, without compromising the minimum level of reliability established. The results obtained with the LRFD calibration data, presented a good approximation with the load factor φ = 0.90, except for the distortional mode. With the LSD calibration data, values well below the specified were required in order to achieve the required level of reliability. It was also found that the load factor γ = 1.25, in the format of the Brazilian standard, could reach the safety requirements established for all buckling modes.

Resistance Factor Calibration for Perforated Cold-Formed Steel Compression Members

“…The Direct Strength Method The Direct Strength Method can be used to obtain axial compressive forces in cold-formed profiles. This is a method that uses properties of elastic buckling to calculate resistance (Toledo, 2021). To identify the buckling modes and their respective critical loads, software based on the finite strip method can be used, such as the CUFSM (Constrained and Unconstrained Finite Strip Method) adopted in this study.…”