The council's specialist engineers Mott MacDonald devised the alternative stabilisation plan which will bring savings of £24m and has now been chosen to replace the existing Pell Frischmann scheme.
H&F commissioned Dr Steve Denton, Head of Civil, Bridge and Ground Engineering at consultants WSP, to compare the two options to stabilise the bridge’s cast iron pedestals. He concluded that the one proposed by Mott MacDonald would be technically superior, implemented more rapidly and more cost efficient than the £30m scheme presented by Pell Frischmann.
As well as saving £24m and reducing the works programme to 46 weeks, the new plan – which has been favourably reviewed by Heritage England – is expected to reduce the need for temporary closures. Engineers believe it will also avoid the need to divert the gas mains on the bridge for the stabilisation work.
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The proposal was presented to engineers and officials from the Department for Transport (DfT) and Transport for London (TfL) at a meeting with Dr Steve Denton and H&F engineers held on 9 August 2021.
The bridge was reopened to pedestrians, cyclists and river traffic on 17 July. Safety experts have stated that the use of the temperature control system, which enabled the reopening, can only be temporary.
In order to move at speed to begin the full stabilisation works, H&F Leader Cllr Stephen Cowan has agreed and signed an Urgency Report.
The Mott MacDonald solution involves the use of elastomeric bearings which allow any pressure to be applied equally to all four corners whilst protecting the vulnerable 134 year-old cast iron structure.
Dr Denton said the Mott MacDonald proposal benefits significantly from the insight gained from the refined pedestal analysis engineers have done over the last year.
H&F expects to keep the bridge open to pedestrians and cyclists for the vast majority of the duration of the works, but there may be short programmed periods of closure to allow some works to take place safely. Advance warning of any closures to minimise disruption will be given.
H&F is developing a Memorandum of Understanding (MoU) with the DfT and TfL incorporating financial proposals to share costs of the work between the three bodies.
The pedestrian stabilisation plan is the first phase of works on the bridge. The second phase will involve extensive strengthening and full restoration and will allow the bridge to reopen eventually to vehicles.
