Specifying cold-formed steel for resilient buildings

All images courtesy ClarkDietrich

by Greg Ralph

With the number of weather-and climate-related disasters in the United States on the rise, the engineering and construction industries have rightly prioritized a focus on adopting methods for designing resilient buildings able to withstand hurricanes, wildfires, flooding, and other natural events. According to the National Oceanic and Atmospheric Administration (NOAA), there were 22 such events in 2020 to affect the country, with losses exceeding $1 billion each. This marks a new annual record, shattering the previous record of 16 events that occurred in 2011 and 2017.

Among the numerous strategies for designing resilient buildings, material selection is of particular importance—putting the specification community in a uniquely impactful position to help mitigate the risks associated with extreme events. A recent report from the National Institute of Building Sciences (NIBS) reveals an 11-to-1 payback for pre-disaster investments that include compliance with modern building codes versus the prior generation of codes and requirements.

When it comes to framing, there is no more resilient option than cold-formed steel (CFS). By analyzing resiliency in the context of the built environment, this article will explore the various attributes of a resilient structure, and make the case for why CFS performs best in each scenario.

‘Resiliency’ defined

Put simply, resilience refers to a building’s ability to withstand, respond to, and recover rapidly from extreme events in a cost-effective manner. Of course, fortifying a structure against hurricane force winds and minimizing loss from fire present entirely unique sets of design challenges. With so many potential forces at work against a building, it is important to take a holistic approach to resilient design.

A joint report from the U.S. Department of Homeland Security (DHS) and NIBS lays out five key attributes comprising resiliency: safety, security, durability, environment, and energy conservation. These attributes are presented as basic requirements for addressing natural and man-made hazards, as well as the environmental conditions of the building’s location. The building’s resilience corresponds directly to how well these attributes enable the structure to meet these demands.

Let us take a closer look at these attributes and how CFS is uniquely suited to addressing the design challenges of each.

Safety

The first attribute of a resilient building is whether it can protect occupants during a life-threatening event such as a hurricane or earthquake. CFS has a number of inherent properties that help ensure a building remains intact during and following an extreme event.

  1. It is highly ductile. CFS can easily bend or stretch without breaking when force is applied to it, and later return to its original shape without losing its material properties. This gives it a higher degree of resistance to lateral loads, uplift, and gravity loading, such as those imposed on a structure by seismic or high wind events.
  2. It has the highest strength-to-weight ratio of all commonly used framing materials. When CFS is formed into a C-shape, like a stud, the bends act as stiffeners and increase the strength of the steel dramatically, providing a significantly greater strength-to-weight ratio than that of dimensional lumber. This inherent strength, plus the fact cold-formed steel is such a relatively light material, also makes CFS-framed structures less susceptible to the forces of inertia that wreak havoc on buildings during seismic events.
  3. CFS is non-combustible. Since it will not burn, the material is eligible for use in Type 1 buildings (constructed with concrete and protected steel) where fire-resistance standards are most stringent. According to the Steel Framing Industry Association (SFIA), both load-bearing and non-loadbearing CFS-framed assemblies are fireproof up to four hours when subjected to tests conforming to ASTM E119, Standard Test Methods for Fire Tests of Building Construction and Materials. Cold-formed steel has also displayed resilience against fire exposure in tests that follow rigorous National Fire Protection Association (NFPA) 285, Standard Fire Test Method for Evaluation of Fire Propagation Characteristics of Exterior Non-load-bearing Wall Assemblies Containing Combustible Components, protocols.
  4. It is consistent. Wood and concrete have a number of variables that can affect their performance, but once a steel stud has been formed it will remain straight with no change to the thickness, width, or other dimensions, as well as strength and stiffness. Building professionals can be assured CFS framing members, produced under a third-party certification program, will arrive at the jobsite certified to comply with all standards.

Durability

Last year saw a record number of weather- and climate-related disasters that caused damage in excess of $1 billion each. As the specifier community looks for ways to design resilient buildings to limit the impact of such events, cold-formed steel (CFS) is an ideal material choice because of its ability to withstand, respond to, and recover rapidly from nearly any extreme event.

The second measure of a building material’s resilience is its durability, or how long it can be exposed to outside elements with minimal wear or damage. A key component of a resilient building is one that is designed to have a long life. Particularly in areas where atmospheric moisture, flooding, or any other inadvertent exposure to water is a threat, CFS is well-suited to help buildings stand the test of time.

Cold-formed steel is corrosion resistant, does not retain moisture, and will not harbor mold growth. When materials are underwater for any length of time, many are not salvageable when flood waters recede. CFS utilizes zinc or similar coatings to boost durability and will last hundreds of years before its corrosion resistance deteriorates. For areas prone to frequent flooding, CFS framing can be the difference between salvaging a structure or needing to completely gut and rebuild.

Of course, any level of moisture within a wall cavity can quickly become a structural and a health problem. Cladding failure or plumbing leaks can also create significant problems within a structure. The Environmental Protection Agency (EPA) states there is a 24- to 48-hour window to effectively reduce the potential for mold propagation following exposure to water. That time window can be even shorter if the materials used to build the wall absorb and hold water. This is not a problem with cold-formed steel, which is inorganic and does not function as a food source for mold. Also, CFS is dimensionally stable in a moist environment and will not warp like lumber does when it gets wet, so walls and floors remain plumb and level.

Finally, cold-formed steel is one of the few building materials that is completely impervious to termites and other pests in any climate or building type. According to Orkin, termite damage in the United States results in more than $5 billion annually. Not only are these infestations costly, but they can also compromise the integrity of the structure and limit its ability to respond to some of the more immediate events discussed previously in this article.

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