Abstract
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.
Highlights
Cold-formed steel (CFS) is the usual term for steel products molded by coldworking processes performed around room temperature using a bending brake operation, press brake operation or cold roll forming
North American Specification (NAS) includes design provisions for Load and Resistance Factor Design (LRFD) that is used only by the United States and Mexico, and Limit States Design (LSD), whose use is limited to Canada
This article shows a study of the level of reliability of CFS beam designed by the Direct Strength Method (DSM) or the Effective Section Method (ESM) available in Brazilian code
Summary
Cold-formed steel (CFS) is the usual term for steel products molded by coldworking processes performed around room temperature using a bending brake operation, press brake operation or cold roll forming. For the North American Specification, the resistance factor for cold-formed steel flexural members, φ=0.90, was calibrated with the First Order Second Moment (FOSM) method (Hsiao, 1989). The calibration data for LRFD are the following values for the nominal live-to-dead ratio (Ln /Dn), the load combinations, and the reliability index: Ln /Dn = 5, 1.2Dn + 1.6Ln, β0 = 2.5. 2. Strength prediction methods resistance factor, φ=0.90, given in this code shall be used to determine the available flexural strength, for both LRFD and LSD formats. This article shows a study of the level of reliability of CFS beam designed by the Direct Strength Method (DSM) or the Effective Section Method (ESM) available in Brazilian code. The assessment of the φ resistance factor was performed using the First Order Reliability Method (Hasofer and Lind, 1974), with LRFD and LSD calibration data.
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