March 1999
Executive Summary
Cold-formed steel is particularly suitable for residential floor framing systems. Conventional floor systems are usually constructed of more expensive, older growth lumber to meet the loading and span requirements. In addition, floor systems are often excluded from energy efficiency considerations since they are mostly contained within the building thermal envelope. Therefore, cold-formed steel (CFS) floor framing represents an effective utilization of this material within the context of traditional home building practice in the United States. However, there are some technical barriers that unnecessarily limit the use CFS residential floor construction such as the lack of horizontal diaphragm shear values used to design for wind and earthquake forces.
This report establishes appropriate design values for CFS horizontal diaphragms in support of safe and affordable housing design. Very few, if any, horizontal diaphragm tests have been performed on CFS floor systems. The need for diaphragm shear values has been primarily identified in instances where buildings are required to be engineered for higher risk regions of the United States (i.e. hurricane-prone coastlines and earthquake-prone areas). Furthermore, the steel joists used to construct the floor diaphragms contain large pre-formed holes to support an effort to develop a highly functional CFS floor system that meets both engineering and certain constructability requirements such as the routing of ductwork and large sanitary drain pipes. These innovative CFS joists provide similar structural performance in resisting gravity loads to
those without holes as confirmed in a separate study.
Prepared for:
U.S. Department of Housing and Urban Development
Office of Policy Development and Research
and
Dietrich Industries, Inc.
and
National Association of Home Builders
Prepared by:
NAHB Research Center
Upper Marlboro, MD
56 pages