French government blames concrete deterioration – but structural engineers point to a design oversight

Industry experts have cast doubt on the findings of a report into the cause of the collapse of Terminal 2E at Charles de Gaulle airport in Paris, which said deteriorated concrete was probably to blame.

The interim report, which was published on July by the French transport ministry, suggested that steel struts connecting the outer steel reinforcement structure punched through weakened concrete in the inner shell.

The report said the building “folded like a wallet” in the vicinity of the failed connection on the north side of the terminal. It indicated that further investigations would focus on differential expansion between the concrete and steel caused by temperature differences on the inside and exterior of the building.

Chris Wise, director of structural engineer Expedition Engineering, said this explanation sounded unlikely.

He said: “What doesn’t sound plausible is that one piece of concrete got weaker over time. The temperature variations between the outside and the inside aren’t sufficient for the structure to fail.”

John Roberts, director of engineering firm Babtie, agreed that temperature changes were not a likely cause. He said: “It’s possible the steel was varying much more in temperature than the concrete and weakened it, but it seems very unlikely after a year.”

Temperature variations aren’t sufficient for the structure to fail

Chris Wise, Expedition Engineering

Henry Bardsley, an engineer at Paris firm RFR, dismissed the deteriorated concrete theory and suggested that poor concrete reinforcement design where the steel strut connects to the concrete may have caused the disaster.

The precast concrete section that failed was unusual as it had a large cut-out in it to accommodate a walkway allowing passengers to get to Terminal 2E.

Bardsley said: “The behaviour of the concrete module was substantially modified to accommodate the link bridge, so the failure occurred in an atypical place. There’s been an oversight in the way the reinforcement was detailed for this special case.”

Bardsley suggested that it was a mistake to adopt the standard modules used elsewhere in the terminal for the walkway access section because it was not easy to adapt a building for a special case.

He said: “I don’t think the special case was checked as thoroughly as the standard elements, which often happens. When you have a standard precast element you should not adapt it but specially design it for its purpose.”