Brief
Engineers used an off-site replica for testing before applying custom concrete to strengthen the four cast-iron pedestals of the UK’s Hammersmith Bridge. Cracks in the pedestals were found to be widening two years ago, and the bridge was closed to traffic, but now pedestrians and cyclists are free to cross and a full reopening is expected in February.
Insight
Critical work to stabilise the Hammersmith Bridge has been completed this week, with engineers strengthening all four pedestals using “bespoke” concrete.
The stabilisation programme was planned, trialled and designed off-site, using a replica pedestal.The bridge has been permanently closed to all traffic since cracks widened in its cast iron pedestals in August 2020, sparking concerns that it could suffer a “catastrophic failure”. It is the culmination of years of neglect and underfunding.
The bridge has been reopened to pedestrians and cyclists and FM Conway has been carrying out stabilisation work to the structure. Stabilisation works on the bridge are now due to be finished by the end of February 2023, following a delay acquiring steel from Ukraine due to the war.
This week, the pedestals containing micro-fractures were reinforced with the unique concrete mix. The four cast iron pedestals, one on each corner of the bridge, bear the weight of the structure.
The Grade II listed pedestals’ exterior aesthetic has been maintained by pouring concrete inside their hollow centres – rather than altering their appearance. This was a difficult task, because concrete normally reaches a high 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.
It was also necessary for the concrete to flow strongly enough to get into the pedestals’ 19th-century nooks and crannies while maintaining its strength. So “super-plasticisers” ensured it flowed well, and small steel fibres made the concrete stronger.
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