Buro Happold helps build spectacular Sackler Crossing
Consulting engineer Buro Happold has provided the engineering design for the Sackler Crossing, the spectacular new bridge in London’s Royal Botanic Gardens, Kew which opens to the public tomorrow (17 May).
The bridge has a deck made up of black granite sleepers supported at a minimum height above the surface of the water. It curves round an island in the lake in a very gentle S-shape and is lined by almost 1,000 bronze posts which act as balustrades. Each of these bronze fins are smoothed and contoured to fit in the pedestrian’s hand, instead of a rail across the 70m bridge.
It is situated at the west of Kew Gardens and is the largest element of plans to attract more visitors by making a previously under-used area more accessible. The bridge’s elegant design, which gives the impression of floating above the waterline, is intended to blend in with, and complement, its setting.
Buro Happold’s bridges group worked on the project, providing the detailed engineering design and specification, advice throughout the manufacturing and commissioning process as well as project management.
This is the first bridge designed by London-based architect John Pawson, who is renowned for his minimalist style. His previous projects range from restaurants and houses to Calvin Klein’s flagship store in Manhattan, airport lounges for Cathay Pacific in Hong Kong and a monastery in the Czech Republic.
“This really has been an exceptional project to work on,” says Simon Fryer, associate in Buro Happold bridge engineering group who led the project for the practice. “It’s been challenging in a lot of ways but I think we’ve helped create an amazing structure, true to the architect’s vision,” adds Fryer.
In order to meet demands for a very high quality finish on such a prestige project and the close tolerances necessitated by the design, Buro Happold has project managed construction and worked very closely with the civil engineering contractors and component manufacturers.
One of the biggest risks Buro Happold had to manage was making sure the piles were in the right place to meet up with the steelwork. “Due to the clay soil of the lake bed, the piles couldn’t be removed once inserted and so it was vital the contractor accurately positioned them. To allow for a degree of error, we designed the structural frame to allow for up to 10cm movement. But in the end, the piling went smoothly and all the piles were placed accurately,” says Fryer.
“As well as being very demanding technically we’ve had the constraints of working on a World Heritage Site within London’s over-crowded road network, for a very high profile client on a prestigious project. And all this took place under the gaze of BBC cameras, filming for the next series of ‘A Year at Kew’,” says Fryer.
Unusually, Buro Happold oversaw construction of a full-scale mock up of a section of the bridge. This had benefits of proving the validity of the design and the complex manufacturing process for the bronze uprights in particular, and allowed testing of modifications and some experimentation for the build team. It also helped to demonstrate to firms tendering for work on the project exactly what was required of them.
One of the key visual aspects of the bridge is the 564 black granite sleepers, which measure 120mm by 120mm by 3m and weigh 130kg each. To accommodate the curve of the bridge, the gaps between them taper across the width of the deck. These are precisely bolted onto the steel structural base, which rests on nine 457mm diameter driven steel piles. The piling took place in January.
Each of the posts has required a great deal of precision engineering. The 990 uprights are made of aluminium bronze, which has the appearance of gold and has excellent corrosion and abrasion resistance. Each upright was cast and then flattened and finished to form a rounded, ergonomically contoured top. The uprights each have a gap of 10cm between them which, depending on the angle of viewing, appears and then disappears, again helping the structure blend in with the surroundings.
Sets of four or five uprights have a backplate fixed onto it that can be bolted to the side of the structural steelwork. To conceal this connection, small granite downstand blocks which have been precision cut from the same stone as the deck are dowelled into the side of the sleepers. Each downstand has an integrated LED light which helps the site come alive after dusk.
The bridge is called the Sackler Crossing in recognition of the foundation that enabled its construction, the Dr Mortimer and Theresa Sackler Foundation. As well as being an attraction in its own right, it is hoped the bridge will help draw visitors to parts of the gardens not frequently seen.
Design team
Client:
Royal Botanic Gardens, Kew
Architect:
John Pawson
Buro Happold services:
Bridge engineering, infrastructure and environment;ground engineering, project management
Civil engineering contractor
Balfour Beatty Civil Engineering
Piling contractor
Green Piling
Quantity surveyor
Jackson Coles
Lighting design
Spiers and Major
Electrical Design
Atelier Ten
Planning Supervisor
Goyne Adams
Bronze specialists
Copper Alloys
Granite supply / installation
Stonepave / Stoneguard
Steel fabrication
‘N’ Class Fabrications
Notes to editors
Photos of the bridge are available on request – please contact the Buro Happold press office.
Press office and practice information at www.burohappold.com
Contact:
Neil Wilks
Press officer
Tel: 01225 321764
Email: neil.wilks@burohappold.com
Buro Happold background info
Buro Happold’s bridges group is among the acknowledged leaders in modern bridge design and has completed many projects for local authorities, private developers, contractors and architects in the UK and abroad.
The group’s experience covers lightweight pedestrian bridges, steel and concrete highway bridges, light rail bridges and viaducts, and moveable bridges over water.
On every project the group’s aim is to produce an elegant and economical solution that is practical to construct. To ensure the bridge is structurally robust, the group carefully analyses its static behaviour and dynamic response. The long term durability of structures is also considered through careful specification of materials and detailing.
One of the group’s most recent projects is the Greenside Place bridge in Edinburgh which won the Special Award at the Institution of Structural Engineers’ 2005 awards.
Buro Happold is a multi-disciplinary international practice of consulting engineers established in 1976. It offers civil and structural engineering, mechanical and electrical engineering, quantity surveying, building services and environmental engineering, health and safety management, infrastructure and traffic engineering, ground engineering, façade engineering, fire engineering, computational fluid dynamics analysis, disability design consultancy, project management, urban design and a range of specialist CAD services.
Royal Botanic Gardens, Kew
Kew Gardens is a major international visitor attraction and its 132 hectares of landscaped gardens attract over one million visitors per year. Kew was made a UNESCO World Heritage Site in July 2003 and represents over 250 years of historic landscape. The site houses over 40 listed buildings and other structures including the Palm House, Temperate House, Orangery and Pagoda as well as two ancient monuments, Queen Charlotte's Cottage and Kew Palace. RBG, Kew is a world famous scientific organisation, internationally respected for its outstanding living collection of plants and world-class herbarium as well as its scientific expertise in plant diversity, conservation and sustainable development in the UK and around the world. www.kew.org
John Pawson
John Pawson was born in 1949 in Halifax, Yorkshire. After a period in the family clothing business he moved to Japan, where he stayed for several years working as a teacher and spending time in the studio of the designer Shiro Kuramata. On his return to England he enrolled at the Architecture Association in London, leaving to establish his own practice in 1981. John Pawson is closely identified with the search for simplicity that has been characterised as Minimalism. His designs explore fundamentals – space, light and materials – and avoid stylistic mannerisms. His career to date has spanned a wide variety of projects, ranging in scale from a compact apartment for the writer Bruce Chatwin and a house on Mallorca for the art dealer Hans Neuendorf, to Calvin Klein's flagship store in Manhattan, airport lounges for Cathay Pacific in Hong Kong and art galleries in London, New York and Dublin . In September 2004 the church of a new monastery in Bohemia designed for monks of the Cistercian Order was consecrated in a ceremony which coincided with the project's exhibition in the British Pavilion at the 2004 Venice Architecture Biennale. Current commissions include private houses in Europe and the US, a condominium in New York for Ian Schrager and a new residential tower in San Francisco. Work on the Monastery of Novy Dvur in Bohemia is ongoing.
www.johnpawson.com
