|FISSURES Investigators found dense and deep cracks in the concourses concrete shell near walkway openings to the main terminal.|
By mid-April, Aéroports de Paris will decide whether to demolish or repair the partially collapsed concourse at Paris Charles de Gaulle airport. To assist in determining the fate of the structure, which failed May 23, 2004, and killed four people, AdP will have its studies independently checked, in compliance with recommendations of the commission that investigated the failure.
AdP is planning changes, in response to findings and recommendations of the four-person commission headed by engineer Jean Berthier (ENR 2/21 p. 10). The commission found that procedural shortcomings as well as structural deficiencies contributed to the collapse. In response to that, AdP will separate in-house contracting and design activities.
Having ruled out faulty concrete, reinforcement or foundations, the commission identified four possible weaknesses in the then two-year-old, 650-meter-long concourse vault, that led to collapse: concrete cracks, possibly from construction caused by insufficient or badly placed rebar, accentuated structural deflections; lack of structural redundancy; weakness in the shells footing beams/supports; poor positioning of external struts.
Weakened by such factors, the shell was at risk of collapse, triggered both by concrete creep creating high localized stresses and thermal cycles aggravating the cracking, concludes the commission. Click here to view chart
While most of the vault is symmetrical, the collapse zone was special. It included three vault openings for walkways from the main terminal building. These openings existed to either side of a central building connecting the concourse to Terminal 2E proper.
The concourse is enclosed by 10 separate concrete shells separated by narrow glazed strips. Shells are made of 4-m-wide arches spanning 26.2 m between supports. The 30-centimeter-thick arches were assembled in precast segments, structurally connected on site.
Arches are united by a floor-level beam on either side of the concourse, supported by columns every 8 m. The vault is stiffened by external, curved steel tensile elements supported on the concrete by struts. These struts press on bearing plates within shell recesses.
The first sign of failure was concrete falling, probably between two struts, at a solid shell among walkway openings. Some 90 minutes later, a solid arch section on the north side around the walkways broke in bending. At almost the same time, a section of beam opposite fractured and fell to the ground. Six arches collapsed at 6:57 a.m. on May 23.
The terminal complex was designed and its construction was managed by AdP. Detailed design was by outside contractors. The commission recommends verification of designs of such complex buildings by independent mathematical modeling, as is done with civil engineering works. And, when the project manager and owner belong to the same organization, their relationship should be defined contractually, it advises. The commission also calls for a "rethink" on fee levels to secure adequate design resources.
The investigation, which did apportion blame, was based on documentary evidence and inspections of the remaining concourse. The team did not visit the collapse site during a parallel judicial investigation.