Four pedestals strengthened by bespoke concrete
The concrete being poured into the pedestals on Hammersmith Bridge. Picture: HF Council
The prolonged project to bring Hammersmith Bridge back into full service has made an important step forward earlier this month.
The 135-year-old Hammersmith Bridge was further stabilised after engineers successfully strengthened all four pedestals using bespoke concrete.
The team of engineers leading the project described this as critical work which required meticulously planning and trials off-site using a replica pedestal.
This has allowed the pedestals containing micro-fractures on the bridge to be reinforced with the unique concrete mix.
The four cast iron pedestals, one on each corner of the bridge, bear the weight of the structure which, because of its unique design, is one of the most expensive bridges in the country to repair.
The engineers have maintained the Grade II* listed pedestals’ appearance by pouring concrete inside their hollow centres which added to the difficult of the task because it had never been attempted before.
Concrete normally reaches a higher temperature when it sets. However, the cast iron pedestals are vulnerable to the stresses that heat causes, so engineers used a special low carbon material to keep the concrete’s curing heat low.
The concrete also had to be able to flow strongly enough to get into the pedestals’ 19th-century nooks and crannies, while maintaining its strength.
Engineers included ‘super-plasticisers’ into the concrete mix to ensure it flowed well, and small steel fibres made the concrete stronger.
Concrete normally has to be shaken or poked in order to ‘compact’ and set into the desired shape. Due to the fragility of the fractured pedestals, this was not an option.
The engineers have instead used ‘self-compacting’ concrete which sets with its own weight.
The concrete mix was tested on-site to ensure the correct fibre content and flowability before 40 tonnes of it was successfully poured into the pedestals to stabilise them for further works.
Engineers monitor the pouring of the concrete into a pedestal. Picture: HF Council
The next step for the pedestals is to inject grout into the top of each and attach temporary steel plates. This will provide extra support for the pedestals.
Then, steel reinforcements will be mounted to the points, or saddles, where the bridge’s chains are attached.
The steel shipment was delayed by the Ukraine War but it has now arrived at the fabrication factory in the north east of England, where it is being cut welded and machined into shape.
Finally, the team will jack the saddles up and replace the corroded seized bearings.
Earlier this month Hammersmith & Fulham Council agreed further plans for the full restoration of the bridge which includes advancing a proposal for a temporary double decker structure to allow it to open for motor traffic sooner than expected.
According to the Hammersmith Society, before work on installing the double decker structure can begin a gas main needs to be diverted and this is believed to be a major project.
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November 8, 2022