Saving infrastructure - strengthening the Hammersmith Flyover

The ambitious and innovative phase 2 strengthening works, led by Ramboll, were completed in 2015 and saved 75,000 tonnes of carbon. The project extended the life of the Hammersmith Flyover by 70 years with no requirement for major maintenance work.
Built in 1961, the 16-span, 622m long Hammersmith Flyover is considered the first major segmental precast post-tensioned highway structure in the UK. It carries the four-lane A4 arterial road into central London and is a major link road to Heathrow Airport.
In 2011 inspections identified significant corrosion of the steel tendons leading to the unprecedented and immediate closure of the flyover. Phase I emergency strengthening enabled the bridge to re-open ahead of the London 2012 Olympics.
Phase 2 strengthening of the Hammersmith Flyover (HFO2), was a phenomenally complex £100m programme including innovative engineering solutions to install a full new prestress without removing the original. With 70,000 users every day on a key strategic route into London, the structure, which had been deteriorating due to significant corrosion, presented many technical, logistical, programme and political challenges. Strengthening the flyover prolongs its life and results in no major maintenance being required for many years.
The bridge owner, Transport for London (TfL) appointed Ramboll and Parsons Brinckerhoff in a joint venture to begin design work across the portfolio, costing around £200m to deliver. The entire HFO2 delivery team consisted of TfL, Costain, Ramboll–Parsons Brinckerhoff joint venture, Freyssinet, Structural Systems/Hevilift and Flint and Neill.
The work, which was carried out with minimal traffic disruption simultaneously included:
  • Changing drainage and improving road restraint systems, finishing with waterproofing and resurfacing the deck
  • Replacing the bearings upon which the entire structure sits and replacing the massive central expansion joint with a new comb joint
  • Making the structure independent of the original prestress with the installation of a new prestressing system that could be replaceable in the future
Pioneering material technology raises the bar in concrete repair
We used pioneering post-tensioning, construction innovation and development in materials technology to deliver a new prestressing system to make the bridge independent of the original post-tensioning, without removing it (believed to be the first time this has been done).
The innovative use of ultra-high performance fibre reinforced concrete (UHPFRC) as a key element in the post tensioning strengthening system has set a precedent for extending the life of key structures using advanced concrete with new techniques.
Importantly, the project restored the bridge to its full load-bearing capacity, enabling heavy traffic transit without restrictions for the rest of the structure’s extended lifespan. Compared to alternatives, such as long-term restrictions or replacement.