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Strong argument

Letters

It is stated that the square column heads (of the supports to Charles de Gaulle Terminal 2E) are wrapped with carbon fibre laminates to 'contain unexpectedly high bursting forces' (NCE last week). It is also stated that experience in wrapping square columns is limited.

It should be understood that to contain bursting pressures, external carbon fibre reinforcement will behave entirely differently on square and circular columns.

On circular sections such reinforcement is very efficient as it is able to work in hoop tension and a relatively small amount of reinforcement can be very beneficial. On square sections it is not possible to generate hoop tension forces in the same way without considerable deformation, which will often result in fibre fracture.

In such circumstances one solution is to transform the area of the square column requiring strengthening into a circular or elliptical section, externally reinforced with carbon, aramid or glass fibre.

This can be achieved using external FRP (fibre reinforced polymer) permanent formwork, incorporating the fibre reinforcement and avoiding the need for on-site laminating.

Such a solution, known as 'FibreShell' was developed by CETEC Consultancy (now part of White Young Green) and used successfully to strengthen 24 bridge columns on the A19 in Teesside.

David Kendall (M), director of specialist structures, White Young Green Consulting, Coopers House, The Horsefair, Romsey, Hampshire SO51 8JZ

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