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Beam of light


Using 'out of date beam designs' (NCE 24 February)?

Brunel- Please think again.

As the engineer checking the new steel-concrete composite bridge being launched at Paddington I have been following intently the findings on Brunel's cast iron bridge over the canal at Paddington.

I have carried out my own calculations on Brunel's structure. To me they indicate that rather than being out of date, Brunel used his famed engineering logic to overcome the problem confronting him.

Far from being worried about compression, he actively encouraged it to offset cast iron's untrustworthy tensile capacity.

Brunel's beams are arched and have a clever detail at the springing to transfer both vertical and horizontal loads.

The relatively large top bulb raised the arch axis further above the relatively flat soffi t, increasing the arching action to the extent that there is no tension in the lower flange of the beam under normal conditions.

Furthermore, the top flange is encased in a strong structural concrete surround, possibly the earliest recorded use of a composite metal-concrete bridge. Not so out of date then!

David Collings (F), technical director, Benaim, David.Collings@benaimgroup. com

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