Negative Tactics of Concrete Promoter Infuriate Steel Boosters
...Charles J. Carter, AISC chief structural engineer. "But our work on fire, blast, progressive collapse and related topics," continuing with various publications and design guides, "began well before the events of Sept. 11, 2001," he adds.
Structural engineers who work with both concrete and steel systems agree. David Scott, the new chairman of the Council on Tall Buildings and Urban Habitat and a principal in the New York City office of Arup, calls the alliance's message about fire, nonsense. "What the building community has learned...is that tall office buildings that have no sprinklers and no fire protection on columns will not perform well in a fire," he says.
Even veteran concrete promoters are distancing themselves from the alliance. George Barney, senior vice president for market development and technical services at Portland Cement Association, Skokie, Ill., says: "PCA's 90-year reputation is built on technical excellence and integrity. That's our culture. We do not indulge in negative promotional tactics, nor do we disparage competing materials."
|Best of Both. Convention center has steel roof and concrete framing below,|
The alliance's message "is a source of confusion," says Michael Mota, PCA's New York regional structural engineer. "There's a place for both materials."
The alliance began fomenting the brouhaha as far back as April 2004, when Margrill sent out a press release via e-mail promoting a New York City Concrete Promotional Council seminar, on 505 Fifth Avenue. The building was touted as the first concrete commercial highrise in New York City—one initially designed in steel. "New York skyscrapers used to be built of steel," said the release. "Not anymore! From now on, cast-in-place reinforced concrete will be the material of choice in the Big Apple."
The claim was spurious. There are at least seven structural steel or hybrid (steel and concrete) office towers recently completed, under way, out for bid or in planning in New York City, reports AISC.
Still, the message was repeated in various industry publications, taking the local debate national. "It is critical that owners, architects, structural engineers, and developers make informed decisions based on accurate information, not misrepresentations spread by representatives of competing systems," replied AISC's then-president, H. Louis Gurthet.
The straw that broke the camel's back for AISC was the alliance's marketing blitz after a recent highrise fire in Madrid. The campaign included a full-page magazine ad. It began: "A demonstration of cast-in-place reinforced concrete over steel construction was the recent fire at Madrid's Windsor Tower."
Scott Melnick, AISC's vice president of communications and editor and publisher of AISC's Modern Steel Construction, shot back with an editorial: "Their latest fairy tale tells the story of the Windsor Tower in Madrid and how it was consumed by a fire that raged for 36 hours. In their story, they report how the building had a concrete frame below the 21st floor and it remained intact, while the building's steel frame from floors 22 to 30 collapsed. There are just a few problems with this story, however. The steel in the building was simply an unprotected steel perimeter framing system primarily supporting the cladding. Second, both the unprotected perimeter framing system and the concrete beams and columns experienced a similar collapse...."To further dispel such stories, AISC's Carter notes a survey of fire-induced collapses in buildings worldwide, performed for the National Institute of Standards and Technology. "The majority of buildings that suffered fire-induced collapse were in fact reinforced concrete," he says.
The alliance's push for concrete cores is self-serving at best, he adds. If society prioritizes hardening of cores, it can be done with steel frames with masonry infill, concrete shear walls or steel plate shear walls.
Choice of framing is not about safety, say designers. "You can provide adequate safety using either material, following a proper design and performance standard," says Ahmad Rahimian, president of WSP Cantor Seinuk, New York City.
And for many projects, such as convention centers, stadiums, airports and skyscrapers, the solution is often a hybrid system. "The question is not whether the building should be in concrete or steel but how to use the two most effectively," says Rahimian.