Unified Flexural Resistance Equations for Stability Design of Steel I-Section Members: Overview

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, simultaneously improving their accuracy and generality. This paper provides an overview of these comprehensive developments with respect to the stability limit states. The updated AISC and AASHTO flexural resistances are, with minor exceptions, fundamentally the same. However, the organization in AASHTO facilitates the streamlined design of typical welded I girders. These members are often singly symmetric, have relatively thin webs, may utilize material with smaller yield strengths for the top flange and/or web, and are typically composite in their final constructed condition. Conversely, AISC emphasizes the streamlined stability design of noncomposite nonhybrid compact doubly-symmetric I-section members. This paper highlights the overall continuity of and the fundamental background to the new AISC and AASHTO provisions. The combined AISC-AASHTO rules are presented as a single set of flowcharts applicable for all types of steel I-section members. This comprehensive approach to the design equation developments leads to numerous improvements in the consistency and accuracy of the various specific provisions.