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Wednesday23 July 2014

Drawing board: Taunton Castle bridges by Moxon Architects

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Moxon Architects’ sensitive and creative thoroughfares enhance one of Somerset’s historic sites

Moxon Architects has designed a family of three bridges to improve pedestrian links through a sensitive heritage site within the centre of Taunton.

The bridges are part of a broader plan by client Project Taunton to upgrade the landscape of Goodland Gardens, positioned between the River Tone and the grade I listed castle, which contains the Museum of Somerset. Moxon’s bridges will span the castle moat, the Mill Stream and the Tone itself, providing enhanced, accessible routes through the site and improving links from Castle Green to the river.

Taunton Castle bridges by Moxon Architects

Moxon kept the bridges as a background element to the grounds.

In such a sensitive site close to a variety of quirky and historic buildings, Moxon aimed to keep the bridges as background elements that were as simple as possible. The three crossings are united by a common design approach despite the different structural solutions of viaduct (Moat), supported beam (Mill Stream) and tied arch (Tone), and the varying immediate contexts of heritage, parkland and waterside respectively. They share a material palette of porphyry stone (also used in the Goodland Gardens’ landscaping), glass, steel and concrete, and all are designed with engineers Flint & Neill Partnership.

“All three bridges are based around the same cross-sectional principles whereby a flat soffit is combined with a shallow inverted ‘V’ to describe a concrete structure with a very narrow-edge profile. This in turn carries the deck surfacing of stone and glazing, with glass parapets contained within a protective band of steel on all exposed edges,” says Moxon director Ben Addy.

Taunton Castle bridges by Moxon Architects site plan

The £350,000 Moat Bridge is a 37m-long ramp skimming over the dried up moat, passing between the castle and the Wyndham Lecture Hall. The slight curve pulls it away from the castle, passing just 2.5m from the hall and tapering from 5m on the Castle Green abutment to 2.6m at Goodland Gardens to the north, climbing 1.8m along its length.

“The false perspective set up by the taper, combined with the gentle curve, is contrived to visually shorten the uphill journey to the square while apparently prolonging the downhill stroll into the gardens,” says Addy.

The bridge is supported by a series of 5 piers of variable span, carefully positioned to avoid archaeologically sensitive areas and designed to leave as small a footprint as possible. The walkway is porphyry stone in the middle with toughened glass on either side and glass balustrades. Its glass treads are illuminated by LED lighting, which also creates a bright edge along the lower parapet.

“The castle is the star. The bridge is much more reserved, genuflecting towards the turrets,” says Addy.

Taunton Castle bridges by Moxon Architects

Moxon aimed to keep the bridges as background elements that were as simple as possible

At 12m long the Mill Stream bridge span was greater than the distance between the piers on the Moat Bridge and so required a different structure, conceived as a picturesque garden bridge. Moxon proposes a single span with a shallow humpback beam formed into the reinforced-concrete deck structure along the centreline of the deck and matching the bending moment of the span. The ends of the beam taper into the deck and are surmounted by hardwood benches that provide seating and prevent the inadvertent use of the beam as a ramp. Several bollards — also in stainless steel — prevent vehicles entering the bridge.

For the Tone Bridge, the structure is a tied arch along the centreline spanning 35m and 4m wide, again with integral seating. Both this and the Mill Stream bridges will replace existing non-compliant structures. The Tone Bridges also has similar benches terminating the spring points.

Work has begun on the Moat Bridge, which should be completed by the summer. Moxon hopes the other two will follow.

Illuminating the decks

How LED strip lighting produced a striking effect

Integral lighting will illuminate the glass treads at the perimeter and sides of the bridge decks.

The 31mm glass build-up, which includes 8mm of anti-slip glass and two layers of 10mm structural glass, is supported in a stainless-steel frame on the reinforced concrete bridge structure.

Taunton Castle bridges by Moxon Architects

Glass treads on the bridge decks are lit by integral LEDs, which also create an illuminated deck edge.

At the 200mm-thick deep edges, the concrete tapers to create a cavity for the LED strip-lighting fittings and power unit beneath the deck.
The toughened glass balustrade is translucent below the deck level, giving a horizontal line of light when seen at night.

The deck panels are toughened laminated glass with a translucent interlayer and are separated from the porphyry strip paving by a stainless-steel fixing strip that unbolts to allow access to the LEDs.

“It will be like standing on an obscured ice cube,” says Moxon’s Ben Addy.

The edges of the glass balustrade are protected by steel cover strips that double as handrails and return down at either end to protect the outer edges from damage

Taunton Castle bridges by Moxon Architects

Section detail
1
Stainless-steel hand guard
2 Low-iron toughened glass balustrade panel
3 Stainless-steel fixing strips
4 LED strip-light fittings
5 Glass fixing
6 Lighting power unit, one for every six strips
7 Toughened laminated glass deck panels with anti-slip treatment and translucent interlayer
8 Porphyry paving
9 Reinforced concrete

 

Project team

Architect & bridge lighting designer Moxon Architects
Client Project Taunton
Structural engineer Flint & Neill
Landscape architect (for wider Goodland Gardens scheme) LDA Design
Contractor (for Moat Bridge & Goodland Gardens) Britannia Construction
Project manager Peter Brett Associates

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