STRESS GRADIENT ON WEBS OF CEE AND ZEE SECTIONS Submitted to:

Distortional buckling of cold-formed steel C and Z members in bending remains an unaddressed problem in the current North American Specification (AISI 2002). When the compression flange is not stabilized by fastening to panels or sheathing, such as in negative bending of continuous members (joists, purlins, etc.) and wind suction on walls and panels (without interior sheathing) members are prone to distortional failures. Adequate experimental data on unrestricted distortional buckling in bending is unavailable. It is proposed to extend a recently completed experimental project on local buckling of C and Z members in bending, to a second phase on distortional buckling. Further, it is proposed to begin work on understanding the role of restraint in distortional buckling both experimentally and numerically. The experimental work may be completed by using geometry similar to that of the Phase 1 testing, but removing the through-fastened panel attached to the compression flange. Subsequently, exploratory work on fastener details and panel stiffness may be pursued. The experimental data will help develop and validate an efficient and reliable design procedure for C and Z members in bending with and without panels attached to the compression flange failing in local or distortional buckling and form the basis for more advanced design methods that account for situations of partial restraint