LRFD resistance factor for cold-formed steel compression members

Abstract

This manuscript summarizes recent work to determine if the LRFD resistance factor for cold-formed steel compression members can be increased above its current value of 0.85. An experimental database of 675 concentrically loaded columns with plain and lipped C-sections, plain and lipped Z-sections, hat sections and angle sections, including members with holes, was compiled. The predicted strength of each specimen was calculated with the American Iron and Steel Institute's Main Specification and the Direct Strength Method, with the Direct Strength Method making more accurate strength predictions, especially for columns with partially effective cross sections. The LRFD resistance factor, calculated with a first order second moment reliability approach, was consistent with that currently specified in the code for both the Main Specification and the Direct Strength Method. Capacity predictions of columns failing by the distortional buckling limit state were more accurate than columns failing by global buckling or local–global buckling interaction. The test-to-predicted strength ratios for single angle columns were highly variable, with capacity predictions becoming excessively conservative with increasing global slenderness.