professor ben schafer's thin-walled structures research group - johns hopkins university


Inelastic bending in cold-formed steel members


Note: The research reported on this page was funded in part by the National Science Foundation.


Research Abstract

Inelastic bending capacity exists in cold-formed steel beams, despite their fundamentally thin-walled nature. In this research a simple design procedure to account for this increased bending capacity is proposed as an extension to the Direct Strength Method of cold-formed steel member design. Using an experimental test database of over 500 flexural tests on cold-formed steel beams approximately 100 tests are found where the bending capacity reaches 95%My or greater including observations as high as 118%My, where My is the moment at first yield. Using elementary beam mechanics, and assuming elastic-perfectly plastic material, the inelastic compressive strain at failure is back-calculated for the tested members. The tested members are augmented by a detailed finite element study of inelastic local and distortional buckling and the inelastic strains as well as the peak moments sustained are examined. The models demonstrate the limitations of the elementary mechanics model which can predict average membrane strains in the compressive flange reasonably well, but maximum membrane strains and surface strains are significantly larger. Simple relationships between local and distortional cross-section slenderness to predict average inelastic strain demands and a relationship between average strain demand and inelastic bending strength are established. These relationships are combined to provide direct design expressions that connect cross-section slenderness in local or distortional buckling with the inelastic bending strength of cold-formed steel beams.


Project Materials

SSRC Paper (pdf) and presentation (pdf) - April 2007

Research Report provided to AISI (pdf) - July 2008

J. of Structural Engineering Paper (under revision) - August 2010

AISI Ballot (spec) (commentary) - Passed! - July 2010


last updated 08/16/10