Disproportionate collapse guidelines for U.S. Department of Defense (DoD) buildings were first introduced in 2001 to provide design requirements for reducing the potential of progressive collapse for new and existing DoD facilities in an extreme loading event, such as blast. The guidelines are published in the Unified Facilities Criteria UFC 4-023-03, Design of Buildings to Resist Progressive Collapse, and are applicable to buildings with three or more stories. Since cold-formed steel (CFS) framing is used in mid-rise load-bearing wall structures for DoD facilities such as barracks, design professionals need to learn practical methods to analyze and design CFS framing to resist disproportionate collapse. This presentation will provide the main concepts of structural design to mitigate the effects of disproportionate collapse in buildings and will also explain the differences between direct and indirect methods of design. Focusing on CFS load-bearing wall buildings, the presentation will discuss how to qualify the structural components of the building (walls, floors, and roof) for disproportionate collapse analysis. A worked design example for a multi-story building using the Alternate Path analysis will be presented with a focus on sizing framing members and connection details.


Nabil A. Rahman, Ph.D., P.E.
FDR Engineers, PLLC

Nabil A. Rahman, Ph.D., P.E.Dr. Rahman is a principal at FDR Engineers in Raleigh, NC. He currently serves as a member of the American Iron and Steel Institute’s (AISI) Committee on Specifications and the Committee on Framing Standards. He is a past chairman of the ASCE-SEI Committee on Cold-Formed Steel Structures and a past chairman of the Cold-Formed Steel Engineers Institute (CFSEI). He was the first recipient of CFSEI’s John P. Matsen Distinguished Service Award. Dr. Rahman has a wide range of experience in the design, fabrication, and installation of CFS framing, as well as product development and software development. He has served as a blast consultant on multiple CFS projects, including load-bearing wall barracks buildings and CFS roof structures. He is a named inventor on seven U.S. patents and is the author of more than 50 research papers and technical notes.