Construction has begun on a novel bascule road bridge that has a 19-meter-long, diagonally split opening span at Poole Harbour, England. Hochtief U.K. Ltd., Swindon, has some 20 months to complete the 140-m Twin Sails bridge under a $28-million contract.

Rendering: Poole Council

Unique design features overlapping box girders in lieu of a conventional bascule.

The roughly 30-m-long opposing tapering steel-box-girder spans will pivot upward to allow boats to enter the harbor. When closed, the tip of each 1.5-m-deep span will cantilever over the opposite support by about 10 m.

This arrangement overcomes the need for pins to connect a conventional bascule bridge’s leaves, which meet at midspan, says Peter Curran, project manager with structural designer Gifford & Partners, Southampton. Wilkinson Eyre Architects, London, is part of the design team.

To avoid differential deflection on either side of the deck’s diagonal divide, the design includes brackets. Being static, the brackets will demand less maintenance than moving pins, adds Curran.