The new bridge has 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. It will link the inner relief road to the newly-completed bypass, and provide a focal point for the regeneration of central Gloucester.

DavyMarkham has over 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. These include the 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.

The bridge 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.

Contract delivery is scheduled for the end of the year, in advance of the planned bridge opening in Spring 2008.