FAILURE TO understand punching shear failure was one of the key factors in the partial collapse of Charles de Gaulle airport's Terminal 2E in Paris, British engineers said this week.
Punching shear has been identifi d as one of the main factors in the collapse on 23 May 2004 (News last week).
But French designers have little guidance on how to combat it, and punching shear failures are rare.
'Here in the UK there has been a lot of research into punching shear as part of the development of flat slab construction by the concrete industry, ' said concrete consultant Dr Jonathan Wood.
'And there have been a number of failures - the most recent being the partial collapse of the Pipers Row car park in Wolverhampton nearly eight years ago.' (NCE 27 March 1997) Wood, who investigated the Pipers Row collapse, pointed out that many engineers still did not understand that punching shear produced a brittle failure, and that there is no redistribution of local forces.
Wood and Waterman Group managing director Bob Campbell criticised the design of the cast in steel socket fixing intended to transfer loads from the external steel struts into the 300mm thick shell of Terminal 2E.
'This anchorage appears to reduce the effective thickness and shear resistance of the shell by almost 36%', said Campbell.
'In the area of failure the composite panels appear to be carrying higher roof loads. This could have increased punching shear stresses by up to 50%.' 'No wonder the investigators listed this recessing of the anchorages as one of the factors in the collapse.' Wood also expressed concern about the sensitivity of the design to errors during the assembly of the composite wall panels.
'Aligning the struts accurately is vital. Any misalignment could build in dangerously high stresses, ' he said.