DavyMarkham - News
DavyMarkham Engineers Movement for Gloucester's New Lift Bridge

Sheffield heavy engineering company, DavyMarkham has gained a £750,000 contract for the mechanical, electrical and hydraulic elements of a spectacular lifting bridge over the canal at Gloucester. Designed by Bristol architects White Young Green, St Ann Way Bridge will dramatically enhance the city's transport system, linking the inner relief road to the newly-completed bypass, and provide a focal point for the regeneration of central Gloucester, being led by the Gloucester Heritage Urban Regeneration Company. The contract was awarded by leading civil engineering construction company, Alun Griffiths Contractors, and the bridge project itself is being funded and managed by national regeneration agency, English Partnerships, supported by the South West RDA.

The bridge is an elegant bascule design with a single counterbalanced 28m movable span, stiffened by tensioned cables attached to a tubular steel gantry and raised by means of two hydraulic cylinders. DavyMarkham will be responsible for the bridge's main pivot bearings and brackets, hydraulic deck operating machinery, tail locking assemblies and electrical control equipment. It will also provide vehicular and pedestrian barriers, CCTV and PA systems, and an operator control desk for regulating bridge traffic and deck open/close routines.

DavyMarkham boasts more than 150 years' industry experience of engineering movement into large steel structures, acquired through the design and fabrication of giant tunnel boring machines, mine hoists and water turbines, and has latterly applied these skills to building bridge mechanisms that lift, swing and swivel. Employing modern finite element analysis and 3D modelling software, coupled with an in-depth knowledge of static and dynamic loads, torsion, resonance, weather and other forces imposed on moving bridge structures, the Sheffield company has been involved in such notable projects as the award-winning Gateshead Millennium Bridge, the unique corkscrewing Paddington Basin Helix Bridge, the arterial Selby By-Pass Swing Bridge, Hull's historic Wellington Street Swivel Bridge and, now, Gloucester's St Ann Way Lift Bridge.

Pivot bearing support brackets (left) and a cylinder clevis being manufactured at DavyMarkham's Sheffield engineering works for Gloucester's new St Ann Way lift bridge.

Gloucester's urban regeneration scheme, aimed at creating a 'step change' in the city's prosperity, involves seven main development areas, including the massive £200m Gloucester Quays scheme, the focal point of which will be a new bridge spanning the Gloucester and Sharpness Canal. As slimline as possible to preserve the existing historic views, it will carry a single carriageway road, with shared pedestrian and cycling routes one either side, and provide a 6m draught to allow the majority of boats to pass beneath when lowered, although it will be raised for tall-masted vessels negotiating the main 12m-wide navigation channel.

The bridge deck, being supplied separately by structural steelwork company Rowecord, will be fabricated from carbon steel beams and sheet steel deck plate, which will be mounted on pivot bearings and bracketry produced by DavyMarkham. A substantial counterweight will be located at the tail end of the span to assist the lifting mechanism, which comprises two 2000mm stroke x 420mm bore single stage, double stroke hydraulic cylinders. These cylinders will be of extremely rugged construction suitable for an exposed environment and corrosion protection of the piston rods will have a design life of sixty years.

In operation, the deck will rotate around a horizontal axis on the west side of the canal and, once in the fully lowered/road open position, it will be supported by two nose bearings and two tail locking mechanisms; the latter will engage into slots at the rear of the bridge leaf and the bolts operated by dual 340mm stroke x 200mm bore hydraulic cylinders, actuated when positioning sensors detect fully lowered status. When the bridge is opened to river traffic, the counterweight span descends into a pit behind the main pivot bearings, coming to rest against sprung buffers and again held in the raised position by the tail bolt. The hydraulic system will be similar to that specified by DavyMarkham for the Millennium Bridge and under normal operation two pumps will be used to raise/lower the deck, although in the event of a single pump failure the bridge can still be operated at half speed.

As part of its overall MH&E (mechanical, hydraulic and electrical) responsibility, DavyMarkham will supply all electrical controls, switchgear and cabling for St Ann Way Lift Bridge, including a control panel complete with HMI screen for automatic bridge operation and individual manual control of hydraulic pump motors, navigation lights, CCTV and the PA system. It will also source and supply four vehicle barriers and flashing wig-wag signals, pedestrian gates, three-aspect navigation lights and five CCTV camera units for regulating bridge and canal traffic.

Contract delivery is scheduled for the end of the year, in advance of the planned bridge opening in Spring 2008. According to English Partnerships, the completion of the St Ann Way Bridge link will generate much needed infrastructure improvements and provide a new and distinctive landmark for Gloucester, with which DavyMarkham is proud to be associated.