Security
Weather-related events are not the only potential threats buildings must be prepared for. Many, such as terrorist attacks, are man-made. The DHS/NIBS report considers blast resistance and ballistics as measures of building resiliency when it comes to security.
Determining a building’s level of protection against an explosive threat can be complicated. The U.S. Department of Defense’s (DoD’s) Unified Facilities Criteria (UFC) program developed guidelines to minimize the threat of mass casualties in the event of a terrorist attack on federal buildings, but these guidelines have also been adopted by many private sector projects. Mitigation strategies include maximizing standoff distance, preventing building collapse, and minimizing hazardous flying debris. Recent research demonstrates the overall stiffness and strength of cold-formed steel can be utilized to resist blast threats using conventional construction methods that add little cost to traditional designs.
Cold-formed steel’s performance against progressive collapse was recently demonstrated in the AIT Barracks project in Monterey, California. The 10,219-m2 (110,000-sf) facility was commissioned by the U.S. Army Corps of Engineers to serve as a modernized, private-sector residence. In addition to seismic considerations, the structure was required to adhere to DoD Unified Facilities Criteria (DoD UFC) 4-010-01, Minimum Antiterrorism Standards for Buildings, requirements for blast loading applied to the exterior framing, as well as DoD UFC 4-023-03, Design of Buildings to Resist Progressive Collapse, With Change 3.
Progressive collapse is defined by the American Society of Civil Engineers (ASCE) as the spread of an initial local failure from element to element, eventually resulting in the collapse of an entire structure, or a disproportionately large part of it. To meet DoD UFC progressive collapse requirement for the exterior walls of the AIT Barracks, the project team ran the CFS joist framing from demising wall to demising wall. The end joists at the exterior wall were then designed to support the wall and roof loading above. This allowed large sections of exterior wall framing to be removed, while still providing vertical support to the structure above. Additionally, structural steel tubes were designed in line with the joist framing at three end locations where the floor and roof were supported by the stud framing, allowing for progressive collapse requirements to be met if the bearing wall below were removed.
Environment and energy conservation
In addition to offering safety, security, and durability, resilient buildings are also judged on their energy efficiency and impact on the environment. Air tightness, thermal transfer, and the use of renewable energy all play a part. Environmental impact, which is often defined through life-cycle analysis (LCA) and also encompasses issues such as acoustical performance, is another area where cold-formed steel can really make a difference.
Steel framing contains on average a minimum 25 percent recycled content and is 100 percent recyclable at the end of its life. It is highly unlikely to end up in a landfill as other framing materials might. According to the American Iron and Steel Institute (AISI), nearly 70 million tons of domestic steel scrap is used each year in the production of new steel. When structures must be renovated or rebuilt after a devastating event, using a material that can be reused or recycled is beneficial from a cost, convenience, and sustainability standpoint.
Additionally, the steel industry as a whole has made great strides to reduce the environmental impact of manufacturing CFS products. Producing a ton of steel today in the United States requires less than half the energy that was needed to produce a ton of steel 40 years ago, resulting in a 50 percent reduction in greenhouse gas (GHG) emissions.
Designing for a resilient future
A greater understanding of the many forces a building must be able to withstand to be truly resilient reveals why cold-formed steel is a wise investment from a material specification standpoint. Its consistent strength and durability, along with its high ductility and strength-to-weight ratio is uniquely suited to resist seismic and high wind events. The fact it is an inorganic material that will not burn, corrode, harbor mold growth, or serve as a food supply for pests further reinforce cold-formed steel’s resiliency.
As the industry continues to embrace resiliency, it is certainly worth considering how one can incorporate this versatile material into their upcoming projects.
Greg Ralph is vice-president of business development for ClarkDietrich. He is actively involved with the Association of Walls and Ceilings International (AWCI) Construction Technology Council and also serves on the Standards Council for the American Iron and Steel Institute (AISI), the AISI Committee on Framing Standards, and the AISI Committee on Specifications. Addition, he holds active memberships with the International Code Council (ICC) and the American Society for Testing and Materials (ASTM) on committees C11, A05, and E06. He can be reached at greg.ralph@clarkdietrich.com.
