Chicago — According to the American Institute of Steel Construction (AISC), the New York Times got it wrong. In the article, “Skyscraper at Trade Center Rises From the Inside Out” (May 25), reporter David W. Dunlap discusses why the contractor for the new 3 World Trade Center building pushed for a concrete core surrounded by steel framing rather than the more typical (for New York) steel core.
According to the NYT, the reason goes back to the design of the original World Trade Center. They wrongly characterize the original WTC as having a steel core. But the WTC didn’t have a steel core and instead relied on a series of small perimeter columns.
“The World Trade Center towers used an unusual and then-innovative shaft wall core system that was built with layered gypsum board — it was a drywall core, not steel-framed as the New York Times incorrectly stated,” explains Charles J. Carter, S.E., P.E., Ph.D., a vice president and chief structural engineer at the American Institute of Steel Construction.
“The reality is that steel-framed buildings are the most robust buildings on the market today,” Carter said. “The Federal Emergency Management Agency published their report FEMA 439A, which studied the Alfred P. Murrah Federal Building in Oklahoma City. It states clearly that all concrete-framed buildings need special design requirements to make them blast resistant, and that 85 percent of the damage seen there resulted because the Murrah Building’s concrete framing didn’t have it. In contrast, FEMA 439B reported that an equivalent steel-framed building would not have collapsed at all, even without any special treatment in design. Even the Oklahoma City Federal Campus building that was constructed to replace the destroyed Murrah Building shows that steel is more robust and as a result uses a steel plate wall system. Analysis demonstrates it takes a foot of concrete to equal the blast resistance of an inch of steel–and it still would not perform to the same level as the steel wall because the surface concrete always becomes flying debris in a blast, which could potentially injure any nearby people.” (For more information, visit http://tinyurl.com/FEMA439B.)
The decision of whether to select a concrete or steel core or framing system for a modern high-rise is not a safety issue, AISC said. Rather, the determining factors remain the architectural and structural design requirements, construction cost and scheduling, and the preferences of the specific contractor and designer.
According to AISC, steel framing is the preferred construction material for offices in New York City and throughout the nation. In fact, nationwide three steel-framed office buildings are built for every one concrete office building — and the ratio is even higher in New York City.