Edition: U.S. / Global

Weakened Concrete Is Cited in Collapse at Paris Airport

By CRAIG S. SMITH; Ariane Bernard contributed reporting for this article.
Published: July 7, 2004

The partial collapse of a terminal building at Charles de Gaulle Airport outside Paris in May was probably caused by steel support rods punching through the weakening concrete shell of the unusual building, according to a preliminary report released Tuesday.

The report, prepared by an investigative commission at the request of Transport Minister Gilles de Robien, did not assign responsibility for the collapse, which took four lives. It also said it was too early to say whether a design flaw or faulty materials were to blame.

But the commission noted that the stresses acting on the building, Terminal 2E, were of ''great complexity,'' particularly at the point where the collapse occurred, and its findings are likely to fuel further debate over whether the terminal's unconventional design contributed to its failure.

The damaged portion of the building, completed a year ago at a cost of $900 million, is an elliptical tube built with technology developed for underground tunnels. To simulate the pressure of the surrounding earth that keeps the concrete tube of an underground tunnel intact, the architect, Paul Andreu, used steel hoops attached to the outside of the tunnel with short steel rods.

Several of these rods punched through the concrete shell, and may have precipitated a cascade of failures as stresses built up elsewhere, according to the report.

''It's possible that the perforation could have prepared and facilitated'' the progressive weakening of the concrete, leading to its collapse, the report stated. ''It remains to explain the origin of the phenomenon and the reasons for which the accident occurred two years and four months after the construction.''

The commission said it would consider how the materials might have settled over time and whether changing outside air temperatures caused the steel framework to expand and contract against the concrete, which was kept at a more stable temperature by air-conditioning inside. Such movement may have weakened the concrete at the points where it is joined to the framework by the steel struts, causing the struts to punch through the concrete shell.

The commission cautioned, however, that the rods may have perforated the shell during the collapse and that the explanation for the building's failure may lie elsewhere.

The 100-foot section that collapsed, for example, is different from most of the rest of the 2,100-foot building because it has three openings for walkways that link it to another part of the terminal. The report said the building appeared to have ''folded like a wallet'' near the point where the curved wall connected with the three walkways.

''This zone is very asymmetrical and it certainly played a part in the collapse of the structure,'' said Jean Berthier, who heads the investigative commission.

Mr. Berthier noted that the report was based solely on observations from outside the building and from detailed photographs. He said the commission's engineers had not yet been able to enter the damaged building, which is still unstable.

A separate criminal investigation will determine who is responsible for the collapse. The commission's mandate is to determine how the collapse occurred.

The report distanced itself from several other hypotheses floated since the collapse, including the possibility that the pillars on which the building rested had crumbled under its weight or that the soil beneath the building had shifted.

Suspicion had fallen on the pillars when it was disclosed that hairline fractures had been discovered in some during construction, though at a different part of the terminal than the one that collapsed. The commission reported that the pillars at the collapsed portion showed no signs of breakdown.

Separately, a government association that regulates flight schedules said no flights would be transferred from Charles de Gaulle to the smaller Orly Airport as a result of the accident and the resulting congestion of Charles de Gaulle's remaining terminals.

Photos (Photographs by Brad Bellows) Drawing (Illustration by John Papasian) Chart/Diagram: ''Weak Concrete'' A weak spot in the curved concrete shell punctured by a metal strut most likely caused the collapse in the Charles de Gaulle Airport outside Paris in May, according to a preliminary government report. POSSIBLE CULPRIT The metal struts, which expand when heated and contract when cooled, may have weakened the concrete where they intersected it. Diagram of the cross section of Terminal E2 before the collapse highlights the following: Concrete shell Struts Windows and steel frame Concrete piling Bridge Street Level Waiting Area