Steel and concrete are the two most prevalent types of structural support materials used in the commercial construction industry. However, given the recent, troubling increase in the number and magnitude of earthquakes occurring globally, it begs the question: Which material performs better in response to severe seismic forces?
It’s a difficult conclusion to reach, because both materials offer strong advantages. Also, there are other factors that can influence or improve performance, such as steel-reinforced concrete or the addition of bracing. Still, there is enough evidence to demonstrate greater confidence in steel structures.
“The annual number of “great” earthquakes nearly tripled over the last decade, providing a reminder to Americans that unruptured faults, like those in the northwest United States, might be due for a Big One.
Between 2004 and 2014, 18 earthquakes with magnitudes of 8.0 or more rattled subduction zones around the globe. That's an increase of 265 percent over the average rate of the previous century...” *“Worldwide Surge in ‘Great’ Earthquakes Seen in Past 10 Years” by Linda Carroll, NBCNews.com/Science, Oct. 2014
The many benefits of steel for use in construction are widely acknowledged. What is less widely understood is why steel proves to be a better choice in the event of an earthquake.
An important thing to keep in mind is that seismic performance does not suggest a structure will survive undamaged. Rather, it defines a structure’s ability to sustain core strength and serviceability – avoiding collapse – after earthquake exposure. In many cases, the structure may even remain operational and require relatively minor repairs.
Three reasons to believe in steel’s ability to withstand seismic effects
1 Steel has the highest strength-to-weight ratio of construction materials.
Concrete buildings carry more dead weight (load) than steel buildings, and often building failures during earthquakes happen because the dead weight cannot be supported once the ground settles, especially structures built on softer ground. Steel’s relative lightness reduces earthquake loads in the frames and foundation.
2 Steel is much more ductile under stress conditions than concrete.
Ductility refers to a material’s ability to deform under extreme pressure without fracturing. Steel’s capacity to yield and recover (bend without breaking) is second to none. It can absorb the energy of earth movement, especially horizontal movements, which are often more destructive than up and down vibrations.
3 The quality of steel production is more consistent and reliable.
Structural steel members are fabricated in factories providing better quality control, whereas pouring of on-site concrete is subject to labor intensive systems, as well as potential inconsistency in material makeup and weather conditions, that may ultimately impact the overall quality.
With mounting evidence of more severe and unpredictable geologic and climate conditions, a strong case can be made for building with steel.