The £22m Gateshead Millennium Bridge was designed to be the centrepiece of a joint application by Newcastle and Gateshead Councils in a bid to become the holders of the prestigious title ‘European Capital of Culture’ in 2008. The bridge also received lottery funding from the Millennium Commission and funding from the European Regional Development Fund.
The design brief for the bridge required the design to be for pedestrians and cyclists, that ships could pass underneath, that it did not overshadow the view of existing bridges along the River Tyne, and that it did not obstruct the Quayside development. Fairfields was awarded the contract to design a control system capable of operating the bridge within very strict design parameters.
The 850 tonne bridge has a total span of 126 metres and rotates around a pivot on each side of the river, supported by two concrete piers incorporating 19,000 tonnes of concrete with 650 tonnes of steel reinforcement. The concrete foundations go down 30 meters and can withstand a collision from a 4,000 tonne ship travelling at 4 knots. Each pier conceals the three hydraulic rams, five pumps and a control panel required to operate the bridge. Each open and close movement takes a total of four and a half minutes to complete.
The bridge is made up of a pair of steel arches. The curved bridge deck incorporates an inner pedestrian and an outer cycle lane separated by a stainless steel fence with built-in benches that also act as a windbreak for walkers. This deck is suspended above the river by suspension cables which give the deck stability. Access to the two lanes is through gates installed at each end of the bridge. The second arch is the supporting deck that forms an arc over the river.
The North and South piers each house five 55kW pumps; four of which provide the hydraulic power required to lift the bridge. The fifth pump is held in a standby state, allowing any pump to be removed from service for maintenance. Each set of pumps provides a design pressure of 220 bar to the 3 hydraulic rams through fixed creep and proportional flow valves. The gates are closed and the bridge is raised by increasing the proportional flow using an ‘S’ profile to a flow demand of 500 litres per minute. The flow to both sets of rams is modulated to ensure that the difference between North and South ram extensions does not exceed 16mm.
The critical nature of the algorithm required to achieve this result was highlighted at an early stage of the project. No historical data from any other bridge control system was relevant since the Gateshead Millennium Bridge was the first of its kind. The requirement to prevent the bridge from over-balancing in adverse wind conditions was also identified at an early stage in the project. In contrast to the flow algorithm, it was only possible to prove the back pressure algorithm on site since this was the only stage at which the bridge was connected to the control system.
The bridge is lowered using the flow algorithm and a similar ‘S’ profile to a flow demand of 420 litres per minute. The rams act as dampers during the lower cycle to bring the bridge to a controlled stop onto its bearings. The gates are opened and the bridge is re-opened to the public. The physical demands of the bridge operation require that a twist of no more than 0.23° is allowed between the North and South sides of the bridge, despite the fact that the North and South have independent lifting systems separated by the River Tyne. A 13-bit rotary encoder monitored by a Siemens S7-226 PLC measures the angle of rotation on each side of the bridge. An emergency stop condition is generated if the twist exceeds 0.23°.
The innovative design of the Gateshead Millennium Bridge generated much interest and was filmed by the BBC for its ‘Tomorrow’s World’ programme. This episode was broadcast in 24 countries worldwide and provided an excellent showcase for the engineering expertise of Fairfields. 36,000 people lined up on the banks of the River Tyne to see one of the world’s largest floating cranes lift the first tilting bridge into position. Her Majesty the Queen and the Duke of Edinburgh officially opened the bridge in May 2002 as part of the Queen’s Golden Jubilee Celebrations. The bridge has since gone on to win multiple awards from various industries, including structural and civil Engineering societies, the steel industry and for awards for architecture.
When we chose the design for the Gateshead Millennium Bridge, we knew we had something very special. The many awards and accolades it has received for its design and construction, has certainly proved us right. But even though we knew how innovative it was, we have been taken aback by the massive worldwide interest in our bridge.
Councillor Mick Henry
Leader of Gateshead Council