Andy Foster looks at how a versatile metal has been put to use at London's Kew Gardens.
As one of engineering's most versatile materials, expanded metal is frequently utilised for its strength to weight ratio, though this attribute took on an extra dimension for its inclusion as part of an iconic new attraction at London's Kew Gardens.
The £3.5 million, mainly steel Xstrata walkway has been designed by Marks Barfield Architects to offer visitors a walk through the woodland canopy.
Following consultation between members of the design team, which also included structural engineers Jane Wenick Associates, The Expanded Metal Company was called upon to supply bespoke sections of its punched and stretched material to form the floor and sides to the edifice. Built by architectural metalwork specialist, WS Britland, the Xtrata is framed in sections of weathering steel, while the expanded metal provides a barely visible infill.
Crucially, the pattern of expanded metal chosen for the project kept visual intrusion to a minimum whilst still being able to sustain the considerable design loadings that included pedestrian foot traffic, wind and potential snow loadings. This 'lightness' allows the public to enjoy an all round, 360 degree enjoyment of their natural surroundings - the expanded metal having an open area of 79 per cent while resisting both deflection and impact damage.
Bob Oakendon ran the project for main contractor Britland, and comments: "It is a quite amazing structure which enables people to look out across the treetops, or to look down trough the mesh grills of the walkway, at the trees growing beneath you."
One of the most impressive aspects to the use of the expanded metal in the construction of the Xtrata was the creation of a three metre diameter node at the central section of the walkway. This broad circular platform demonstrates the strength of the slender material.
The Project Architect for Marks Barfield, Mr Chris Smiles, reflects: "The selection of expanded metal was driven by a number of factors that encompassed both physical and aesthetic requirements. We were looking for a material which would work with the Corten steel and be galvanised as well as powder coated to match its appearance. Then it also needed to provide a large enough perforation to maximise visibility, but not large enough for stiletto heels to get caught, or for children to be able to climb up the sides".
"The Expanded Metal Company was able to supply a variety of samples offering different appearances and transparencies, while their SupaGrip product had the slip resistance to ensure wet leaves would not be a danger to people on the walkway. It was a cost effective, one stop shop; and the expanded metal will need minimal maintenance."
Tony Kirkham, Head of the Arboretum at The Royal Botanic Gardens, Kew, added: "The expanded metal materials used work extremely well on this project, as the gaps have been made in two sizes and compliment each other in the design.
"From a distance it appears there is nothing on the floor sides where the material has been used, and can be viewed through easily by the visitor."
Expanded Metal was first manufactured on a commercial scale in 1889. Exactly 120 years later the original.
Expanded Metal Company is still manufacturing to the same principals from the original factory. With more than 9000 types of expanded metal mesh, the company services a wide variety of markets across the Northern Hemisphere including aerospace, automotive, defence, filtration and architecture.
The slitting and stretching method which turns a small amount of metal into a lot of mesh, is basically a one stage process resulting in little or no waste.
Enter X at www.engineerlive.com/ede
Andy Foster is with The Expanded Metal Company Limited, Hartlepool, UK. www.expandedmetalcompany.co.uk
