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Sydney Lenssen
The events that dominated my time as editor actually predate the launch of NCE, but the detailed analysis of these events, right from the launch issue, really captures what the magazine set out
to do.
It was the collapse during construction of three box girder bridges of similar design that led to the UK government’s Merrison Committee of Inquiry, which featured on the cover of NCE’s launch issue. The bridges at the centre of the inquiry were the West Gate bridge in Melbourne, Australia which failed in 1972 and claimed 35 lives (pictured); the Cleddau Bridge in Milford Haven, South Wales which also collapsed in 1970 killing four people; and the 1971 failure of a bridge over the River Rhine near Koblenz in Germany that killed 12 people.
Box girder bridge collapses
Box girder construction was rapidly developed in the 1960s and was used on the Severn suspension bridge. Many similar bridges were planned to be built in the early 1970s. Alec Merrison, who was vice chancellor of Bristol University at the time, was charged with leading a team of respected civil and structural engineers to uncover what had gone wrong and make recommendations to prevent further failures.
The first issue of NCE announced that the final report was expected within months but that the team had already acknowledged that allowances for imperfections in the steel and in fabrication of the box girders must be accounted for in the design analysis. Nonetheless, Merrison would not be pressed on what recommendations the final report would set out.
In reality, the industry had many months to wait for the final verdict, which was published in September 1973.
I was in Australia when I heard that the report was imminent and received a call from the Department of the Environment asking me to get back quickly to London to write an article for The Times explaining the findings and changes required. I was surprised that any government ministry could be able to place such an article, let alone on the front page of The Times.
Immediate impact
The impact of the report on the industry was immediate - 26 bridges of similar design already in use and a further 28 under construction had to be strengthened with additional steelwork. Until then traffic lanes would be closed where possible to reduce the load.
The government was concerned that the public would be panicked by the bridge closures. The department did not wish to see a repeat of the public’s shocked reaction which followed the Ronan Point disaster in May 1968.
The reaction from designers was that the report had taken an ultra-safe approach.
The impact of the report on future bridge designs is still felt today as it brought in the process of independent design checking for the permanent design and erection and temporary works for larger bridge structures.
Division of responsibilities
The recommendations also included clearer division of responsibilities between the engineer and the contractor. This saw the engineer directly charged with considering the temporary loadings of the bridge at the design stage, although the contractor remained responsible for the execution of the erection process.
While the report was focused on box girder bridges, the inquiry’s report on the tragic events at Koblenz, Melbourne and Milford Haven had a strong warning for all civil engineers: do not become overconfident and carefully check all procedures.
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The aspect ratio of box girder bridges was similar to aircraft wings, and ex-aircraft engineers were recruited to re-analyse them and devise strengthening schemes. They had the advantage of knowing how to deal with shear lag. The Merrison guidelines were based on Stephen Timoshenko’s “Theory of Plates and Shells” rendered into a form that could be used directly in a design office. It was said that Timoshenko spent his whole career reproducing his lecture notes from the university of St. Petersburg in the early 1900s.
Hi Sid, you haven’t changed a bit – guess you’re still playing squash. Those box girders…they were researching the failures when I was at Imperial in the early 1970s, and still writing stories abt them when I joined NCE in the late 1970s. Enjoyed my time immensely, and relieved to have switched from the worry of designing the next box girder bridge to simply writing about the intrigues of engineering via the great publication that you created …would love to catch up, bill (billoneill@cix.co.uk)