Application of the finite strip method in cold-formed steel member design

The objective of this paper is to explore solutions and provide design recommendations for two practical issues that develop when integrating computational member analysis with the conventional finite strip method (FSM) into cold-formed steel member design utilizing the direct strength method (DSM). First, FSM often fails to uniquely identify the relevant local and distortional member buckling modes. These elastic buckling loads (or moments) are required inputs for predicting the design strength. Second, the recently developed constrained finite strip method (cFSM) which can uniquely identify local and distortional buckling in all cases suffers from its own limitations, specifically (a) cFSM does not yield the same exact solution as FSM even when unique minima exists in the FSM solution, and (b) cFSM cannot include rounded corners in the model of the cross-section. Two methods are examined herein for overcoming these limitations, both of which utilize cFSM in an augmented form. The proposed methods are explored for lipped channel cross-sections both for elastic buckling and for ultimate strength prediction via DSM. Particular attention is paid to methods for handling cross-sections with rounded corners (in both elastic buckling and strength) since cFSM cannot include rounded corners and still meaningfully identify the modes. Finally, based on the study of lipped channel members a recommendation is provided for a methodology that enables automated analysis of cold-formed steel member elastic buckling modes for use in DSM.