In 1969 the Department of Housing and Urban Development (HUD) initiated Operation Breakthrough, a program designed to encourage the development and introduction of industrialization into the housing industry in the United States . Under the Breakthrough program a number of housing systems were selected , evaluated, and constructed on demonstration sites . The National Bureau of Standards, on behalf of HUD, drafted criteria [I]' which were used to guide the development and subsequent evaluation of these housing systems. These "Guide Criteria" contained a provision against progressive collapse under catastrophic loading which was not previously contained in any U.S. code or standard (Progressive collapse may be defined as a chain reaction of failures following damage to only a relatively small portion of a structure) . This report discusses the implementation of this provision.