LOCALISED BUCKLING in the north wall of Paris Charles de Gaulle Airport's Terminal 2E's vault roof was the primary cause of the dramatic collapse four week's ago, it was claimed this week.
Paris-based British structural engineer Henry Bardsley proposed the new mode of failure having studied a previously unpublished set of photographs taken just hours after the collapse.
The photographs, he claimed, showed no sign of the column head failure initially suspected by many experts, (NCE 27 May) and indicated to him that the failure began close to or actually between the openings for escalators.
'Steel stiffening sections which should have been in tension have buckled laterally or have been torn away from the concrete shell, ' explained Bardsley, referring to details he said the photographs revealed.
He said that it was likely that although this buckling could have been partially restrained by the footbridge structures, the concrete shell roof would have broken away at the insitu joint and fallen straight down.
His theory is that as the roof fell it would have pushed the southern composite sections off their column head bearings almost intact. This section then sustained serious impact damage when landing some 1m away from the column feet.
Bardsley said he was passed more than 40 pictures taken by an anonymous airport employee before rescue workers started shifting debris in the search for survivors. He has since passed them on to the official enquiry team.
He said the pictures were much more revealing than most so far published, as they were taken of the north side of the structure which, he said, had more 'extensive and significant damage ' and 'some important clues are visible'.
But Atkins structural design head Mike Otlet, who has studied the collapse over the past few weeks, said it was too early to rule out the original column head failure theory, particularly as recent research has showed that the type of column head wrapping used on the project would have been virtually useless (see page 6).
'This is a non standard area with complex load paths and there are a number of factors which could have triggered failure, ' said Otlet.