BENTS EYED Vault during a troubled construction phase, when columns of concrete bents were reinforced. (Photo courtesy of Eiffel/Laubeuf)

Construction problems with supports of the vaulted concrete concourse that partially collapsed early on May 23 at the year-old Terminal 2E at Paris Charles de Gaulle Airport will likely be a focus of investigations into the cause of the failure, which killed at least four people.

Roughly 30 meters of the unusual freestanding vault enclosing the 650-m- long elevated concourse dropped several meters off its bearings with little warning.

On evidence available at press time, an independent structural specialist suggested faulty concrete bents.

"It looks like the roof is an innocent victim, along with the people inside," he says, requesting anonymity. Noises emanating from nearby structures warned of continuing instability a day after the fall.

State-owned Aéroports de Paris (AdP), which was responsible for the architecture and engineering of the $900-million complex, has not ruled out demolishing the entire concourse if fundamental faults are unearthed.

Serving 22 aircraft bridges, the concourse provides waiting areas in a tubelike space on an elevated concrete slab parallel to the main terminal building. It is enclosed in a flat elliptical reinforced-concrete vault, 30 centimeters thick. The vault is heavily perforated with window openings. A nonstructural aluminum framework supports glazing above the concrete.

The vault is divided along its length into 10 sections with gaps in between to let in daylight. Halfway along the concourse, the vault is interrupted by an "isthmus" building linked to the main terminal. The failure occurred immediately next to the isthmus.

Each of the roof’s 10 sections is made of 17 precast concrete vaults, spanning more than 30 m over the concourse. Though not connected structurally to each other, the 4-m-wide vaults are fixed to previously cast edge beams running between concrete portal frames rising from the ground, much like bents.

The beams’ neoprene bearings, supplied by Paris-based Freyssinet S.A., are seated on notches at the outer corners of over 80 concrete bents, spaced along the concourse. People and vehicles circulate under the bents.

CRUSH Collapsed section of elliptical vault is near the link to the main terminal (above, right, area circled) at Paris Charles de Gaulle Airport. (Photo top left by AP/Wideworld; above right courtesy of AXYZ/ADP)

Under a $32-million contract, Paris-based GTM Construction S.A. built the roof on top of supporting frames. The frames and other substructure formed part of a separate contract by Hervé S.A., Paris. Both contracts ran between April 2000 and January 2003. A separate joint venture of two French contractors installed the external glazing.

GTM erected the 4-m-wide rings of the vaults symmetrically, with two side elements and one at the crown, explains an engineer with Vinci Group, the contractor’s owner. GTM supported the elements on a rail-mounted frame until they were stitched together with reinforcing steel and concrete into spanning shell sections. No structural connections were made between abutting shell sections.

With AdP ruling out terrorism and sabotage, construction defects are seen as a possible cause. AdP concedes that columns had to be additionally reinforced, but...