Before modern engineering and the ability to manipulate concrete and steel, the world of architecture consisted of wood, adobe, thatch, and cave dwellings. We’ve come a long way. Today’s cities reveal skies punctuated by buildings so tall and austere, even architectural tour guides experience the occasional pain in the neck. So, which material reigns supreme in the world of development today - concrete or steel? Both provide numerous benefits. As for whether or not one is better, Buildings lets you determine which side you’re on.
Concrete: The recent announcement by Ground Zero Developer Larry Silverstein regarding safety measures at the new 7 World Trade Center (WTC) building echoes what the concrete industry has been saying for years: Concrete is safer. The building’s core (where elevators, stairs, and power systems are located) will be encased in 2-foot-thick concrete for protection in the event of a fire or terrorist attack. “Cast-in-place reinforced concrete offers outstanding resistance to explosion and/or impact. Moreover, it can endure very high temperatures from fire for a long time without loss of structural integrity,” says Alfred G. Gerosa, president, Concrete Alliance Inc., New York City.
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Concrete requires no additional fireproofing treatments to meet stringent fire codes, and performs well during both natural and manmade disasters. Because of concrete’s inherent heaviness, mass, and strength, buildings constructed with cast-in-place reinforced concrete can resist winds of more than 200 miles per hour and perform well even under the impact of flying debris.
With proper design, engineering, and construction, the seemingly rigid structures built with concrete can exhibit increased ductility - a must in areas prone to seismic activity. However, according to the Skokie, IL-based Portland Cement Association (PCA), the performance of any building during an earthquake is largely a function of design rather than the material used in construction.
Steel: While recent reports issued by the National Institute of Standards and Technology blame the reduced structural integrity of steel for the collapse of the WTC towers, the jet-fueled fires are to blame. Experts acknowledge that steel can soften and melt with exposure to extremely high temperatures. However, with the addition of passive fire protection, such as spray-on fireproofing, buildings built of structural steel can sustain greater temperatures and, therefore, provide additional safety.
Don’t base your opinions about steel’s performance on the events of 9/11. In the October 2003 Modern Steel Construction article “Blast Resistant Design with Structural Steel,” authors Anatol Longinow and Farid Alfawakhiri recall the 1993 WTC attack. The article indicates that the inherent redundancy of the steel frames prevented the structure’s collapse. “We’re seeing a lot of structures constructed taking into account progressive collapse for blast conditions that are designed very effectively and very economically in steel,” explains John P. Cross, vice president, marketing, American Institute of Steel Construction, Chicago.
Steel’s strength and ductility, combined with solid engineering and design, make it a safe choice in seismic zones. “Steel framing does very well under high [wind] loads because it is ductile, which means it has the ability to bend without breaking and can absorb that kind of energy,” says Larry Williams, president of the Washington, D.C.-based Steel Framing Alliance, of cold-formed steel.