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Investigators delay Paris airport wreckage clear-up

WORK TO clear the wreckage of Charles de Gaulle airport's collapsed Terminal 2E is on hold, operator Aeroports de Paris (ADP) said this week.

The company said nothing would be done until the judicial investigation into the collapse was finished.

The probe into why six sections of a concrete vault came crashing down, killing four passengers, on Sunday 23 May is expected to take up to six months.

ADP is conducting its own independent inquiry.

'Until we have discovered what caused this disaster we can't make any decisions about the future of Terminal 2E, ' said ADP projects director Hubert Fontanel.

He said that the rest of the stricken terminal structure is being checked daily for signs of weakness. But it, and the mess of concrete and steel resulting from the collapse, are otherwise being left untouched for the two investigating teams.

The collapse happened in one of two areas of the 680m long terminal that are structurally different from the rest of the building. Terminal 2E consists of 10, 68m long vaults.

Each vault is composed of 17, 4m wide precast concrete arches strengthened against buckling by external steel trusses.

Arches bear onto cast in situ longitudinal edge beams, which are supported on rectangular columns at 8m centres.

Failure of edge support is one of the key issues under investigation (News last week).

Most of the 4m wide arches are structurally independent of their neighbour - they are connected by non-structural locator bolts only. The only parts of Terminal 2E where this is not the case is in the collapsed area and an identical point on the other side of the building's centre line.

At each of these points, the landside vault wall is pierced by three walkways linking to an adjacent terminal hall.

These rectangular section steel tubes are non-load bearing.

Accordingly, vault arches have shear connections at the points where the walkways pierce the structure. This enables the load of the incomplete arches to be carried by those on either side.

How the terminal works

The vault of Terminal 2E is unusual in that it bulges outwards from its springing points, swelling from 27m wide to 32m at mid-height.

This introduces huge buckling forces in the vault's walls, which are resisted by external steel trusses. Vertical load is estimated to be 100t and horizontal load 20t.

The trusses have bolted connections at the tops and bottoms of the vault walls.

Struts connecting the outer chord of the truss and the concrete shell keep the walls in compression.

Arches making up the vault comprise three precast concrete elements, 4m wide and 300mm thick. Wall elements were delivered to site complete with their stiffening steel trusses.

During construction, the walls and crown element of each arch were supported on temporary props while insitu concrete stitch joints and longitudinal edge beams were cast in situ.

Longitudinal edge beams bear onto rectangular columns at 8m centres. Silicone bearings were installed to accommodate movement in the vault resulting from wind, snow and temperature change.

During construction of the terminal building, cracking occurred in the heads of 20 columns as a result of unexpected bursting forces.

As a result, the vault was jacked 1mm to 2mm off the columns while carbon fibre reinforcement was wrapped around the top 300mm.

Carbon fibre wrapping was also carried out on all of the vault's remaining, undamaged columns, as a precaution, in advance of vault erection.

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