Estimating Drift in Cold-Formed Steel Frame Structures

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Over the past decade, the cold-formed steel industry, both in the US and worldwide, has seen a significant increase in number of practical design guidelines and standards developed to facilitate structural design in residential, commercial and institutional buildings. One of these new standards, the 2004 American Iron and Steel Institute (AISI) Cold-Formed Steel (CFS) Design Standard – Lateral Design, provided designers with the necessary tools to better investigate, understand and engineer structures to comply with the wind and seismic provisions of the local building codes, particularly in regions with high wind and seismic risks. Where design for lateral loads is a concern, one important consideration is the distribution of lateral forces in accordance with the relative stiffness of the diaphragm and the in-plane wall bracing. Additionally, in seismic resistant design because interstory lateral displacements (drifts) are restricted, it is necessary to be able to computed expected inelastic lateral displacements. In this paper, the current provisions for estimating the lateral displacement of conventional CFS shear walls are reviewed and discussed. A comparison of inelastic drifts based on the Lateral Standard equations and inelastic estimates using the provisions of the 2003 International building is also presented and recommendations for future research are suggested.