To symbolise London’s hosting of the 2012 Olympic Games, a giant set of Olympic rings have been installed on Tower Bridge, one of London’s most recognisable landmarks.
Against the clock
Hoisting and fixing the rings was not an easy task, and Paul Monaghan, ICE and Municipal Expert Panel member, oversaw this landmark project. Paul told ICE how in just 5.5 hours the rings were hoisted up, suspended, and fixed to the bridge.
Getting to the tower
The aluminium rings, weighing 13.4 tonnes and measuring 25 x 11 metres, were made and assembled at London’s Royal docks. On 26 June 2012, the rings were transported to Tower Bridge, and chain hoists were attached to lift them. Once suspended, the rings were then fixed to the underside of specially designed trusses, using beam clamps.
Retractable rings
The bridge still had to lift to allow tall river vessels to pass, meaning the rings had to be able to retract. This movement is operated by the bridge controllers, who coordinate the rings to move before the bridge is raised. They take about 40 seconds to draw in and the machines operate by motors feeding a cable across the wheel of the truss-frame structure. These pull the rings into a horizontal position, allowing the bridge to lift.
Overcoming further challenges
As well as allowing for ships to pass, the engineers had to take account of the impact of high winds. If wind speeds were to reach above 20m per second, they could compromise the structure of the bridge.
Another obstacle encountered was the discovery of a redundant pipe on the bridge, not identified in the initial survey. However, by fixing the rings 150mm lower than initially planned this problem was swiftly overcome.
An iconic achievement
The Olympic rings project shows how engineers are contributing to making the London Olympics and Paralympics a spectacular event. Although the rings will be removed after the games, the pictures, images and memories of this iconic image will resonate for years to come.