There are more than 1500 sites in Britain where movable bridges exist or once stood. Many are landmark structures, symbols of civic enterprise, often providing the focal point of a major infrastructure project. Over the last decade, Sheffield-based DavyMarkham has been engaged in engineering many new landmark moving bridges, from the Gateshead Millennium Bridge to the Selby By-Pass Swing Bridge, and each has involved complex technical challenges, when translating the architect’s vision into a working installation that will give years of dependable service.
Typical is Gloucester’s newly opened £10 million lift bridge, an elegant, contemporary single-span bridge, with an efficient electro-hydraulic movable deck, which links the inner relief road to the new south-west bypass and provides access to the massive Gloucester Quays £250 million redevelopment scheme. A joint venture involving English Partnerships, British Waterways and developer Peel Holdings, it delivers the essential infrastructure that opens up part of the city that was previously difficult to reach and leads directly to the new Gloucestershire College campus and several other regeneration projects. The 300 tonne lifting deck also creates another spectacular landmark on Gloucester’s changing skyline.
Typical of such major capital projects, it took several years to progress from initial drawings to the official opening and, during that period, it underwent a name change from the original St Ann Way Bridge to the present High Orchard Bridge, which commemorates the site of the Llanthony Priory orchard where the bridge now stands.
DavyMarkham was contracted by civil engineering contractors Alun Griffiths to design and manufacture the mechanical, hydraulic and electrical elements of the bridge, notably the main pivot bearings, the deck operating system, tail locking assemblies and electrical control equipment. It also installed vehicular and pedestrian barriers, CCTV and PA systems, and an operator’s control deck for regulating bridge traffic and deck open/close routines.
The bridge deck, supplied separately by structural steelwork company Rowecord, measures 28 metres long by 16 metres wide and weighs around 200 tonnes, with an additional concrete and steel 100 tonne counterweight in the tail section of the bridge. The deck rotates 69º around a horizontal axis, to allow entry to a 12.5m wide navigation channel, and is driven by two 2000mm stroke, 420mm bore hydraulic cylinders. The structure rotates on two giant pivot assemblies, secured by 75mm diameter bolts, and the whole arrangement is similar to that built by DavyMarkham for the award-winning Millennium Bridge.
In the fully lowered, road open position, the bridge deck is supported by two nose bearings on the leading edge and two tail locking mechanisms at the opposing end, also designed and produced by DavyMarkham. The tail locks are operated by dual 340mm stroke x 200mm bore hydraulic cylinders, which are engaged when positioning sensors detect the deck’s fully- lowered status.
“We are enormously proud to be involved in landmark projects like Gloucester’s High Orchard Bridge. These are prominent steel structures that will be around for many years to come and it’s wonderful for our name to be associated with imaginative designs that help shape the British landscape,” says DavyMarkham MD, Kevin Parkin.
“This type of contract also emphasises our precision heavy engineering skills,” he continues. “We employ modern finite element analysis and 3D modelling software, together with our in-depth knowledge of static and dynamic loads and other forces imposed on moving bridge structures, to perfect and prove specific engineering designs, so that large rotating steel structures like High Orchard Bridge will operate safely, smoothly and reliably. Quite simply, it’s a practical and highly visible example of good British engineering.”
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