Hammersmith Bridge in London is a fine example of engineering expertise. First built in 1887, it crosses the River Thames between Hammersmith and Barnes, and was designed by Sir Joseph Bazalgette. It is 13m wide and 210m long, with a central roadway and pedestrian crossing on either side. It is also London’s weakest bridge, with a 7.5 tonne limit and recent traffic flow, predominately for single-decker buses, has been controlled by traffic lights[1].
Throughout its lifecycle, the bridge has been strengthened and refurbished numerous times. Originally constructed from wrought iron and chains to support its suspension, the bridge underwent major restructuring in 1973. Replacement steel trusses, improvements to the mid-span hangers, and new deck expansion joints gave the bridge an extended life and safe passage for Londoners. However, with the increase in traffic in London, the bridge closed completely, including to river traffic underneath it, in August 2020 due to the size of cracks in the north-east pedestal.
The cause of the cracking extends well into the bridge’s history. Like all suspension bridges, it was designed to move and flex to absorb shocks. However, in the years since WWII, wear and weather have damaged the suspension system which prevents the bridge from moving. This led to vibrations from traffic being driven directly into the iron structure, eventually causing cracks and erosion[2].
The plan to stabilise with a view to reopen to pedestrian, bicycles and river traffic is underway. One proposal by Foster + Partners includes pedestrian and cyclists being able to use the bridge during its repair and restoration. Plans to rebuild incorporate a new raised truss structure built above the existing road deck, and a lower level for pedestrians and cyclists with an upper level for cars and buses. The new truss structure would be assembled in two halves and launched from each side over the existing road, supported on each bank and at two existing piers[3]. Following stabilisation and opening to light traffic, works to rebuild and strengthen the bridge by repairing its structural issues will commence, with this expected to be complete within six years[4].
The damage to Hammersmith Bridge leaves asset management professionals in no doubt of the value in regular and planned maintenance to public infrastructure. Asset management provides a crucial role in mitigating risks such as overall safety to the community and climate change impacts to ageing infrastructure.
[1] Sourced: https://www.fosterandpartners.com/news/archive/2020/11/foster-partners-reveals-plans-for-temporary-crossing-over-hammersmith-bridge https://www.amcouncil.com.au/news/56-member-news/100099-hammersmith-bridge-%E2%80%93-the-plan-to-rebuild.html
[1] Sourced: https://www.hammersmithbridge.org.uk/s/53/the-future