Unified Flexural Resistance Equations for Stability Design of Steel I-Section Members: Uniform Bending Tests

The 2004 AASHTO and 2005 AISC provisions for flexural design of steel I-section members have been revised in their entirety relative to previous specifications to simplify their logic, organization, and application, while also improving their accuracy and generality. This paper evaluates the lateral-torsional and flange local buckling (LTB and FLB) predictions from these and previous specifications versus uniform bending experimental test results. A total of 154 rolled and 123 welded I-section member LTB tests, and 11 rolled and 36 welded I-section member FLB tests are considered. Reliability indices are estimated for load and resistance factor design (LRFD) of buildings based on the test statistics combined with established statistics for material and fabrication bias factors and the ASCE 7 load model. The notional reliability for LTB is found to be reasonably constant and consistent with the targeted level in the first AISC LRFD specification of 1986. The unified equations, combined with a design-oriented procedure for calculation of elastic LTB K factors, are shown to capture the test results accurately throughout the inelastic and elastic LTB ranges, leading to substantial liberalization of the calculated resistances in certain cases. The mean resistances for inelastic LTB and FLB are captured accurately by a linear equation in the corresponding slenderness parameters. The reliability for FLB is found to be slightly higher than that for LTB.