Last month I postulated that incompetence, incubated by France's socialist system, was the ultimate cause of structural failure in Paris' new airport terminal. I cited the square windows in an arched concrete structure, and the use of structural concrete in a building requiring light and visibility. I blamed these unadvisable choices on the political dominance of a powerful but vain designer over the professional engineers charged with ensuring the safety of the building.
Public speculation at the time focused on cracks in supporting pillars during construction. Now there's a new theory:
Detailed photographs taken shortly after the partial collapse of a passenger terminal at Roissy-Charles de Gaulle Airport last month appear to offer an alternative to initial theories that cracks in the concrete pillars supporting the structure were to blame for the deadly accident.
Instead of the pillars, a section of the terminal's curved wall may have been the location at fault.
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in what he described as "today's best hypothesis," Bardsley said that the location of the structure's initial failure might have been elsewhere: in a section of the terminal's curved wall.
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"It appears that there was a bending failure at an insufficiently studied opening in the shell at about mid-height in the flank," where the tubular concourse connected with three pedestrian gangways, he said.
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Bardsley posited that the building's arched concrete roof suffered an "asymmetric," two-stage collapse that began on the north side of the building - an area that was not photographed by the news media on the day of the accident.
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Several of the new images depict the building's deflated blue-gray shell and the three glazed walkways, which appear to have dropped by about 1 meter from their original placement, which was level with the upper floor of the terminal's concourse.
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Ringlike sections of prefabricated concrete are also visible, and Bardsley identified a number of areas where "radial" steel ribs meant to stiffen the structure along an exterior wall had either twisted or had slipped out of their sockets. One image also clearly shows an external steel support boom that is bent by about 90 degrees.
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Bardsley posited that the high "load," or weight, of the walkways, as well as a flaw in the joints that connected the ribs to the concrete shell, caused a "lateral buckling failure" near the walkways.
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Once the wall of the north side failed, Bardsley said, the force of its collapse could have nudged the south side of the arch off its concrete pillars, sending that edge of the span crashing to the ground.
"Insufficiently studied opening?!" Translation of this phrase into plain language constitutes quite a condemnation of the professional civil engineers who were responsible for the "studying." Perhaps they feared for their jobs if they didn't go along? Or maybe they were merely incompetent.
And the explanation that an external steel frame was needed to hold up the "concrete goose," and that implementing the scheme proved problematic, supports my anti-concrete bias for this particular design.
Still no mention of square windows in the curved concrete walls but the fact they could buckle without their steel supports definitely raises the profile of these controversial (at least on these pages) elements.
For his part, the building's high-profile architect Paul Andreu is now witholding any public comment on the advice of his lawyer.
Posted by JohnGalt at June 16, 2004 06:02 PM