Cold-Formed Steel Beam-Columns Experimental Program, Numerical Analyses, Design Code Development, and Design Tools

This paper summarizes the newly proposed Direct Strength Method (DSM) for cold-formed steel beam-columns and introduces the developed design code and design tools. DSM is a robust and flexible design method available in the AISI Specification (AISI -S100) for designing thin-walled steel beams and columns. Currently, no explicit method is available in the Specification for designing under combined actions, as beam-columns are designed using linear interaction equations. As a result, the cross-section stability analyses are performed only under two simplistic stress distributions: i.e., stress due to isolated compression and bending. This study provides an integrated, explicit design method for beam-columns that uses new design expressions but still encompasses the current DSM method for isolated beams and columns. The new beam-column DSM has recently been validated against the results of an experimental program on lipped channels and Zee-sections. Further, nonlinear geometric and material collapse analyses have been performed on the tested specimens to establish a modeling protocol for cold-formed steel beam-columns. Parametric studies using the modeling protocols have been leveraged to validate the proposed DSM for a wide variety of cross-sections. To ease implementation of the new method, CUFSM (a finite strip method program for elastic buckling analyses) has been recently improved to incorporate the generalized definition of the combined actions in the stability analysis and also to provide yield and plastic strength surfaces, which are essential in the new DSM beam-column implementation. The proposed method has the potential to provide a more mechanically sound solution to the strength of beam-columns, increase performance, and enable a new generation of optimized and high strength cold-formed steel shapes across a variety of loading actions.

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