Blast Analysis and Design of Cold Formed Steel Roof Trusses

Cold-formed steel (CFS) roof trusses are one of the most commonly used roof systems in current construction due to their light weight, long-span capabilities, design flexibility, and fast erection times. When used in new DoD construction subject to the UFC 4-010-01 (2013) DoD Minimum Antiterrorism Standards for Buildings, the adequacy of CFS roof trusses to provide the required level of protection against blast loads must be demonstrated through blast analysis or testing. However, the UFC 4-010-01 standard is silent on the analysis methods and response criteria for CFS roof truss systems. This presents a challenge when using this type of roof system in projects subject to blast-resistant design. PEC engineers are leading the industry in the development of appropriate design and analysis methods for these systems.

PEC has developed three analysis approaches for the design of CFS roof trusses. The first is an equivalent static design method used to provide conservative design information for pricing purposes. While we do not use this approach for final design of CFS roof trusses, it allows for rapid sizing of truss systems to provide information for pricing. The second is a simplified SDOF dynamic analysis method that utilizes a detailed structural model to develop a simplified resistance function for the truss. This approach can be used on most common truss shapes and systems and results in lower cost for analysis than more complex finite element analysis. Finally, where complex geometry or loading conditions exist, PEC engineers can employ detailed coupled finite element analysis (FEA) models that allow ultimate design flexibility accommodating even the most complex architectural geometries and loading conditions.

With this multi-level approach, PEC engineers work with our clients to develop a solution that meets the project design criteria and budget. Some of our recently completed projects using CFS roof truss systems include:

• Mess Hall replacement at Marine Corps Base Quantico, VA
• TEC Dorm and Classroom Facility, Air National Guard, Alcoa, TN
• KC-46A ADAL Facility, McConnell Air Force Base, Wichita, KS
• P470 NGIS Visitor Quarters, Naval Air Station JRB, New Orleans, LA
• Specialty Care Clinic, VA Medical Center, Walla Walla, WA

For more information on blast analysis of CFS roof trusses for your next project, contact Dr. Marlon Bazan or Greg Rolater.