Interim Design Rules for Flexure in Cold-Formed Steel Webs

摘要

The design of cold-formed steel webs in flexure is governed by section B2.3 of the AISI Specification. Harmonization of the AISI (1996) Specification with the Canadian Standard (S136 1994), for the development of the new North American Specification (NAS 2001) has brought to light shortcomings in both the U.S. and Canadian documents and lead to the adoption of an interim design approach in the NAS (2001). The interim approach employs the AISI (1996) rules for one class of members and the S136 (1994) rules for a second class. Assessment of the resulting method with existing bending tests on Cees and Zees reveals significant "scatter" in the prediction of cold-formed steel beams and highlights problems associated with ignoring web/flange interaction, as is done in current methods. Determination of the "classes" in which the two methods are employed is presented, as is the rejection of a specific exclusion for sheathed members which was proposed during the development of the interim method. Finally, the practical implications of the new design rules are explored in a design example with the step discontinuity in strength between the "classes" highlighted.