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Pointing out the flaws in design argument

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Glad I wasn't the only one who saw some flaws in the article about building designers risking failure as a means to an end, 'Trial and Error' (AJ 18.4.02).

Bob Owston is quite right (Letters, 25.4.02) - most building failures are caused by leaving something out, either in design, construction or workmanship.

Sir Thomas Bouch's Tay Bridge collapsed in 1879 because the designer only allowed for a wind load of 17 lb/ft sq at a time when designers in the US, like William Le Baron Jenney, were designing for speeds of 50 lb/ft sq on railway bridges and early skyscrapers in Chicago, and Eiffel was using 55 lb/ft sq for his bridges.

Add to this the slipshod workmanship which bordered on the criminal, the deliberate leaving out of fixings, the use of Beaumont's Egg - lamp black, beeswax, iron filings and rosin to fill in holes in the castings - and it was not so much a case of, 'if the longest bridge in the world fell down', but when it did.

Individual parts of the bridge were quite strong. Some of the girders were reused in the rebuilt bridge. They are still in use today, but the completed structure was very weak. This was caused by the engineering concept and the way in which it was all put together.

In a number of respects Ronan Point (pictured) was similar. The original design wind loading put forward by the contractor's engineer for Ronan Point was to have been 17 lb/ft sq (40mph) for a building more than 200ft high in the Thames Estuary. The borough engineer insisted on 24 lb/ft sq (63mph).

The engineer should have been designing for an overall wind load of 45 lb/ft sq (105mph) with peak gusts of 65 lb/ft sq at the top corners of the building.

(para 135 of Inquiry Report).

I am not at all clear how Ronan Point 'collapsed progressively upwards', according to Clive Richardson's article. I always thought the small explosion just blew the loadbearing flank wall outwards leaving no support for the four floors above. Gravity, which has an uncanny effect of always working, just did the rest.

Sometimes we do appear to go round in circles. More than 150 years ago, Robert Stephenson said in an address to the ICE when he became its president that: 'The younger members of the profession would learn more by looking at failures and studying what went wrong and how to put them right than any amount of studying of successful structures.'

Sam Webb, Canterbury

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