The following article appeared in the Surveyor Magazine in July 1998. The text and photographs have been reproduced below with the kind permission of the Surveyor.
Bridges have been the abiding interest of a varied engineering career for David Yeoell, the City of Westminster's Assistant Client Director for Engineering Services and the new Municipal Engineer of the Year. Maureen Rose reports on his major contribution to the needs of the bridge strengthening programme.
Photo:Hugh NuttThe message from many of the leading highway authority bridge engineers has been clear for several years: properly carried out load testing of bridges can save the country millions of pounds in unnecessary strengthening works.
David Yeoell, as chairman of the London Bridge Engineering group (LoBEG), has been a particularly vocal champion of the load testing message for nearly a decade. Now, he is beginning to see the results of all the lobbying, public speaking and assembling of the arguments against the voices urging caution.
In November, the first-ever authoritative guidelines for using supplementary load testing are due to be launched. Meanwhile, work is going on to establish a methodology for safe use of the more controversial proving load test.
Although supplementary load testing is by no means new and is frequently used as part of bridge assessment, there has not previously been any clear guidance on how it should be used for bridges.
Proving load testing, many believe, carries greater potential risks, and members of the national steering committee for load testing of bridges decided that more research was needed.
The result was a Transport Research Laboratory review concluding that a methodology can be developed for using the test safely, but that more work has to be done on specific bridge types before guidelines can be issued.
‘We in LoBEG have always favoured the proving load test, but because of the resistance to it we agreed more research was needed. Even if the guidance just says that some types of structures should not be tested, we will have gained some knowledge of value.’
The steering committee, which Mr Yeoell has chaired for two years, since its first chairman, Andrew Leadbeater, retired, is notable for its inclusiveness, having members from all the country’s major bridgestock owners, as well as academics and consultants.
‘It’s good to see all the different interests coming together, from their different viewpoints and working together on this question,’ he says. ‘I am really passionate about the benefits of people working together and using their different skills to get the best results.’
The scarcity of capital funds for the bridges programme led him to bring people together to develop another innovative partnership, the London Package to bid for TSG for the capital’s bridges.
First taking up the chairmanship of LoBEG in 1988, two years after it was set up, Mr Yeoell has been developing co-ordination of the boroughs’ assessment and strengthening programmes for nine years. Four sector groups, meeting regularly and including representatives of other bridge owners, were followed by a special group to deal with the specific problems of the Thames crossings, ensuring that works are planned to cause minimum disruption to traffic. As well as the owners of all the crossings from Twickenham Bridge to the Queen Elizabeth Bridge, Police, Government Office for London, The Traffic Director and London Buses are all represented.
‘We got people working together, and this general co-ordination was going well. But it was still the Department of Transport dictating where the money for bridge strengthening should go. We each had to put in our own bids and it was pot luck who got what’ he says.
With the need for funds far outstripping the resources available, Mr Yeoell proposed a further step: bidding for one TSG allocation for the whole of London, with the money to be spent by agreement where it was most needed.
This involved ranking the works by priority. So WS Atkins was called in to help devise a strategy, based on risk management that would enable consistent comparisons to be made between different bridges. Each can be judged against a number of weighted criteria, including risk of failure, social impact of restrictions and cost of interim measures.
Photo:Hugh NuttThis has given us a powerful tool he comments. ‘It is robust and it is auditable. It underlies the whole package because we can show that the money is being spent on the bridges most in need of it. The money is not enough, but at least we can make sure that it is all spent, because if one borough falls behind its programme and cannot spend all its allocation, this system allows us to reallocate the money instead of seeing it go back to the Treasury.’
His package system went into action for the 1997/8 TSG round, when £22M was allocated to London and while less than half of the £48M the boroughs bid for, it was at least all spent. This year, the grant has gone down to £15.2M, a situation he describes as ‘very disappointing. It seems we are going to be looking at a lot more weight restrictions in the future’.
Mr Yeoell’s involvement with LoBEG started when he was with the structures division at Bromley, where he spent 13 years before joining Westminster. His work there was varied, but he particularly treasures the memory of being in charge of looking after a group of dinosaurs.
No ordinary dinosaurs, these were survivors of the original Crystal Palace and among the structures remaining in the borough’s Crystal Palace Park.
‘We had a contract with the parks department to maintain the dinosaurs,’ he explains. ‘They are Grade I listed beasts and because of their age they needed a lot of looking after.’
When he moved to Westminster in 1990, the problem of another listed structure landed on his desk, continued to be a top work priority for the next seven years and provided another opportunity to demonstrate the benefits of partnership.
‘Westminster Bridge had been inspected and it was clear that something was badly wrong,’ says Mr Yeoell. ‘A full assessment then showed that its weight limit needed to be brought down to 7.5t.’
A major programme of load testing followed, which, together with careful instrumenting, provided more information about how the bridge worked and enabled a strengthening strategy to bring the bridge up to the 40t standard, to be designed.
Then the contract started going wrong. A great deal more corrosion than expected was found, together with crucial misalignments that had not shown up in the assessments.
‘We had a serious problem. The contract’s first phase was going over time and over budget because of what we were finding,’ he explains. ‘A complete review was needed and the traditional contract method was not suitable in these circumstances. So we sat down with the consultants and contractors, reviewed all the constraints and came up with a lump-sum, fixed-price, fixed-term contract, with all the parties working as a partnership.’
The resulting partnering agreement worked so well that the project came in on time, below budget and with a high-quality result.
‘People can look at the bridge and ask where all the money has gone because it doesn’t look any different. But that is what we aimed for. It’s a Grade II listed structure and we wanted to preserve its appearance exactly.’
The last major scheme in Westminster’s strengthening programme is due for completion this summer, with the strengthening of the historic Lancaster Vaults abutting Somerset House. The vaults are the old flood arches, and the only remaining parts, of Rennie’s old 1815 Waterloo Bridge.
Then it is on from the old to the new, with the replacement of the Hungerford footbridge with two new bridges. A millennium project, for which Westminster is leading its sponsoring Cross River Partnership, the project hit trouble last year with conflict between the authority and the architects’ consortium which produced the design.
Patient negotiation resolved the problems and the project is all set to go ahead. Says Mr Yeoell: ‘It’s going to be absolutely marvellous. The design is for two cablestayed footbridges one on each side of the rail bridge and we are hoping to have the upstream bridge installed in time for the millennium celebrations.’