SECRET TESTS carried out last week on London's notorious 'wobbly' Millennium Bridge have convinced structural engineer Arup that its chosen solution to the opening day sway problem will be accepted by the client.
Last night, around 2,000 volunteers were due to march across the bridge to test the damping mechanism installed to minimise lateral sway. Cleveland Bridge has fitted more than 90 dampers in an attempt to minimise the sway which developed when thousands of pedestrians crowded the bridge during its opening day in June 2000.
The tests were to be observed by WS Atkins, advisor to the London Borough of Southwark and the Corporation of London, and Professor John Newlands of Cambridge University on behalf of the Millennium Bridge Trust.
They were seen as the final hurdle before the £18M crossing could re-open.
But last week, without any publicity, Arup put 700 of its own staff onto each of the three spans in turn, in a larger scale repeat of an earlier series of tests which had satisfied the Arup team that their damping concept would work (NCE 22 February 2001).
On Tuesday, in an exclusive interview, Arup chief executive Bob Emerson said the bridge had performed 'better than expected'.
He added: 'In the absence of any performance criteria in current bridge codes, we had long since agreed with our client's advisors to use figures for maximum lateral accelerations similar to those specified for office buildings.
'Last week, it was impossible to see any lateral movement and, although there was some very slight vertical movement on the southern span the tie-down dampers there were only moving 1mm.'
Readings from 24 acceleration sensors on the crossing provided the final reassurance to Arup last week.
Similar readings from this week's test will be studied by the client's advisors before a final decision to re-open the bridge is taken.
Paying tribute to the 'great job' done by Cleveland Bridge and the US and German damper suppliers, Emerson added: 'We believe that this is the most onerous test ever applied to any footbridge anywhere. Results from this and previous tests will be fed into the appropriate bridge code committees and will ultimately result in the codes being updated.'