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Walking through hoops

working details

Eduard Ross was still a student when he stepped in with a design for a footbridge at Princes Dock in Liverpool In February 2000, Eduard Ross won a competition for a new footbridge at Liverpool's Princes Dock. His scheme - a massive canted wishbone resting on steel ribs with a walkway running through them - beat a number of established practices, yet he was still a finalyear student at the Centre for Architecture at Liverpool John Moores University.

Princes Dock, close to the Liver Building on the east bank of the Mersey, is a massive deep-water dock, built in 1847. Once lined with warehouses, it has been redeveloped with commercial and hotel buildings by the Princes Dock Development Company. The bridge spans 30m, linking the new development to the city.

When Ross won, the Centre for Architectural Research and Consultancy Unit (CARCU) at the university was commissioned to act as architect. Ross then developed the project under the guidance of Ian Wroot, senior lecturer in architecture, who assumed the role of project architect. The structural feasibility was tested by Arup.

Ross's skeletal structure has rugged details which resonate with the great steel cranes and rope blocks that once lined the waterfront.

Reaching the footbridge from the towpath, you pass between the wings of the wishbone.

These fuse together to form a great spine, which rises as you progress beneath it and is supported by curved, rib-like hoops.

To prevent longitudinal spread, the arch is restrained by a pair of 76mm diameter tie rods running diagonally down each side of the row of hoops. The hoops act as compression frames to resist forces from any out-of-balance components within the wishbone arch and tie-rod system.

A series of cladding rails runs horizontally; acting as secondary frames fully welded to the primary structure. The cladding is a visual screen rather than a waterproof shelter, consisting of a series of perforated polyester powder-coated aluminium panels, produced by AME Facades. The deck is formed of extruded aluminium planks which rest on the outer CHS members of a traditional braced horizontal wind girder.

The components were carefully detailed to minimise water collection and salt staining.

The steel component assemblies were further developed by fabricator JSW Construction, by means of the Xsteel software package. The bridge was prefabricated at Cammell Laird's Birkenhead shipyard. When complete, it was taken in one piece across the river on the 'Mersey Mammoth', Liverpool's giant floating crane, then lowered into position and bolted down.

Now in place, the bridge's hoops terminate on the riverside as a huge oval frame on the Mersey, while the spine projects beyond the deck like the prow of one of the great sailing ships which once graced the river.

CREDITS ARCHITECT Liverpool John Moores University - Centre for Architectural Research and Consultancy Unit (CARCU): Eduard Ross, Ian Wroot STRUCTURAL ENGINEER Arup: Richard Houghton QUANTITY SURVEYOR E C Harris LIGHTING DESIGN Jonathan Speirs & Associates MAIN CONTRACTOR David McLean Contractors SUPPLIERS aluminium cladding panels AME Facades;

steel fabricator JSW Construction;

deck NCMP

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