Modal analysis of steel-framed residential structures for application to seismic design

There has been a significant worldwide increase in the use of cold-formed s teel in low-rise residential structures as an alternative to timber. A majo r research project to assess the performance under lateral loading of cold- formed steel frames commenced more than 7 years ago at The University of Me lbourne, Australia, in collaboration with industry and other research organ izations. This paper reports key findings from an extensive experimental pr ogram. It details a particular aspect of the program that uses nondestructi ve dynamic testing to identify the basic dynamic properties of such structu res. Laboratory tests, employing a shaking table, have been conducted on un clad wall panels and a model test house to study the influence of different framing connection types and to assess the influence of nonstructural comp onents, namely, plasterboard interior lining and brick-veneer exterior clad ding. The findings from these tests were verified and further extended by t esting a full-scale prototype house at various stages of construction. This paper presents information concerning typical natural frequencies and mode shapes for such structures. It also details the contribution of nonstructu ral components to the lateral stiffness, which was found to be significant. The results have important implications for seismic design and performance of such structures, even in regions of low to moderate seismicity.