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Whitbybird takes flight

METALWORKS

With a collection of designs taking shape in England and Italy, the Whitbybird team is providing elegant cycle and pedestrian crossings which also encourage users to stop and take in the views

Bridges, within their context, should be considered areas of public space. So much so that the identity of a bridge must evolve from understanding the local history, current issues surrounding the site and the impact that any new crossing will have on the nearby community.

The energetic bridge design team at Whitbybird, a creative multi-disciplinary group of engineers and architects, is busily engaged in a new raft of elegant steel pedestrian and cycle bridges designed to perform as visual additions to the urban spatial and cultural context, as well as serving a primary function by providing vitally needed crossing points.

The Whitbybird team claims that its bridge designs are so diverse that it cannot be labelled collectively as having a typical 'house' style. Nevertheless, and almost in spite of the team, the attention to detailing at points of human contact gives the game away. The quality of materials and detailing to balustrades, alternative decking systems, and thoughtful attention to architectural lighting, along with benches and rest places wherever length and width allow, give each bridge the appearance and status of a quality public space.

Previous bridges designed by the team have already become popular destinations in their own right. The 80m long bench on the York Millennium Bridge is, in good weather, filled by people eating their lunch while enjoying views and fresh air. Maybe in terms of design solution each bridge stands apart, but when it comes to each bridge's role in shaping public space and impact within the life of a community, the stamp is very much that of Whitbybird.

Chelsea Bridge Wharf Link Bridge Span/length45m The graceful cycle and pedestrian Chelsea Bridge Wharf link bridge will link the Thames-side footpath, currently broken by the abutment of Chelsea Bridge.

Whitbybird's design springs a slender mild-steel box girder in an elegant curve out from the river bank, describing a crescent around the abutment of Chelsea Bridge. It connects Chelsea Bridge Wharf on the east side with Battersea Park on the west.

The geometry of the bridge is a tilted part-circle expressed in a simple twisted box section. The bearing connections are key to the balance of the entire structure. Each end is anchored into concrete pile caps deeply embedded in the river wall.

Projecting out over the tidal water 10m from the riverbank at the apex of the curve, the bridge will be supported by two slanting steel piers. Steelwork on the piers is protected by a thick coating of an anticorrosion paint system more commonly used on oil rigs. The propped design gives a simpler, lighter solution than a cantilever, but the structure will still work if one prop is accidentally taken out by shipping impact.

The deck, coated in an anti-slip finish, is 4m wide to allow cyclists and pedestrians to pass comfortably. Distinctive V-shaped steel balustrades stand over the edge of the deck, which is punched with holes. Concealed blue LED lights behind the edge plate, will articulate the edge at night, while reflecting the distinctive curve of the bridge into the water of the Thames below.

The bridge is being fabricated off site in Littlehampton. Installation is planned around the July high summer tides. Lifted onto a barge, the bridge will be brought down the Thames at high tide and floated into position over the two piers. As the tide goes out, the bridge will be slowly guided to rest on discrete pier connections recessed within the soffits.

CREDITS CLIENT Berkeley Homes VALUE £600,000 COMPLETION 2004

Irwell Footbridge, Spinningfields, Manchester Span/length 45 metres This graceful steel bridge across the Irwell is part of the Spinningfields regeneration project in Manchester's city centre. Positioned between two road bridges, it will provide a new circulation link into Salford on the north side and Manchester on the south for cyclists and pedestrians.

The two river banks are at dramatically different heights. The higher, south end of the bridge feeds directly into a public square.

The northern end lands onto existing Victorian brick arches standing directly over the garden of a riverside pub.Views up from the garden led the design team to create a bridge with an especially elegant, lightweight appearance, and an architecturally articulated soffit.

With a Calatrava-designed bridge already in situ to the east, the client was keen to evolve a bridge that had its own sense of place and particular identity. The resultant catenary structure was inspired by the river's own upside-down reflection of the nearby New Quay Street bridge.

A steel catenary cable forms an inverse arch below the curved bridge deck, set on an incline to offset the torsion of the curve.

Tapered steel arms cantilevered off a tubular steel spine that runs centrally along the underside of the deck, provide both stiffness and visual interest. The shallow depth of the catenary was influenced by the requirement to provide river clearance of 4.7m.

The deck itself will be of perforated aluminium planks, and the handrail system is formed from V-shaped tapered stainless steel balustrades supporting a tubular stainless steel handrail with cable infill for safety.

LED lighting below deck level, and coldcathodic lighting in the handrail along the balustrade, will emphasise the lightness of the design as well as illuminating the route after dark.

CREDITS CLIENT Allied London Properties Ltd COMPLETION 2004

Footbridge over the River Cam, Cambridge Extended walkway: total length 200m Span/length: Bridge: 35m clear Whitbybird collaborated with artist Gerry Judah to design this extended bridge that will take pedestrians and cyclists across the River Cam, extending over water meadows that can at times be flooded. The flowing curve of the bridge deck responds to the natural meandering of the river.

The slender deck and arched form respond to the site, minimising the length of approach ramps that had to be gentler in gradient to allow them to bridge over the flood plain. On the ramp, segregation between pedestrians and cyclists is suggested by a change of material in the deck surface. The pedestrian path is formed in lightweight perforated aluminium planks supported on cantilevered steel arms. The resin-bonded cycleway gravel surface rests on a structural steel box deck As the bridge passes over the river, the two decks split apart, with the arch rising between them. The cycleway rises to a high point at the centre, while the pedestrian route levels out. The 'tiered' section will provide, as a result, an excellent vantage point for spectators standing on the bridge to watch rowing events. The physical separation of the two paths over the river also provides maximum safety for pedestrians to stop and enjoy the view. This role of the bridge as a public space is encouraged by the gentle widening of the pedestrian deck towards the centre.

Viewed from a rowing boat on the river, the lightness of the bridge is emphasised by glimpses of the sky through the split deck.

The longer northern approach ramp reverses the sweep of the bridge, its curved shape reducing its perceived length. Structural piers grow into sculpted lighting masts, while small 'bud' spaces provide resting places for both pedestrians and cyclists.

CREDITS CLIENT Cambridge City Council COMPLETION 2006

River Po Footbridge, Turin, Italy Span/length: 70m clear/140m Turin is preparing to stage the 2006 Winter Olympics. The River Po flows between two of the city's squares - Piazza Chiaves and Piazza Carrara. Whitbybird's competition winning design, in association with B&C Associati of Como, bridges the Po to link the two piazzas, allowing access for pedestrians and cyclists. The stunning panorama, with the Italian Alps framing immediate city views, gave rise to a graceful steel box girder footbridge with a soft, sculptural quality.

The elevation is based on three intersecting toroids, creating a pulsing sequence of shallow arcs that span elegantly between tall concrete piers. At the haunch of each arch, the deck measures 1,250mm deep but decreases to a mere 640mm at the point.

Straight in plan with curved edges, the bridge is eight metres wide at the piers, narrowing to five metres at the centre. Two canoe shaped stainless steel benches bridge the widest points in the deck, each supporting a distinctive lighting mast.

The two concrete piers, oval in plan, taper inwards to a slender waist near the top.

Above each waist is a curved Y-shaped walkway support, which has been likened to the spanned shape of a waiter's hand, the thumb and index finger stretched wide support a loaded tray overhead.

The bridge's slender, rhythmic appearance is completed by a stainless steel wire balustrade, with forked uprights that echo the 'waiter's hand' design of the piers. The handrail incorporates strip lighting, casting a soft white light onto the non-slip deck. The decking is punctured at regular points over matching elliptical conical recesses punched into the soffits of the bridge, allowing daylight to pass through during the day, and illumination by blue LED lights at night.

Construction is under way, with the concrete piers already in place, ready for a bridge lift in the early autumn. The full 140m mild steel box girder structure is currently laid out in sections in a site running along the river bank of the Po, being welding by the steelwork contractor using a mobile welding shed mounted on rollers, designed to be moved along the length of the bridge while it is on dry land.

CREDITS CLIENT City of Turin VALUE E2.5 million

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