Converting a Sculpture of Two Horses' Heads Into a Dramatic 30M
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THE FALKIRK KELPIES SOCIETY THE FALKIRK KELPIES Converting a sculpture of two horses’ heads into a dramatic 30m-high landmark on the Falkirk skyline presented an unusual challenge for the engineers involved. Felicity Starr, lead structural engineer for Atkins on The Kelpies project, worked with Andy Scott, the sculptor, on creating the 30m tall horses. She explains how the vision was turned into reality. In 2006, Falkirk Council and mechanism, using the weight of British Waterways Scotland (later, the sculptures to displace the Scottish Canals) were trying to required amount of water to resolve twin, related problems: flood the central lock and lift how to regenerate derelict boats into the canal network. industrial land between Sketches were made of the Grangemouth and Falkirk, and sculptures, based on ‘kelpies’ – how to overcome a low bridge the mystical equine creatures carrying the M9 motorway over said to inhabit the lochs and the River Carron that meant that pools of Scotland. The idea was canal traffic could only enter or sold, but the sketches convinced leave the Forth and Clyde Canal everyone that now was the time at low tide. The answer to the for the engineers to defer to a former was the new 350-hectare professional artist. Helix urban park; the answer to Andy Scott was a natural the latter was a short extension choice. He had already to the canal with a new lock, established a reputation for large with the two projects merging public sculptures, working mainly into one. in welded galvanised steel. He A plan evolved to create frequently sculpts horses: his two sculptures for the park, 4.5m-tall Heavy Horse was already which would at the same time a popular landmark beside the form an integral part of the lock M8 motorway near Glasgow. With the main structural frame complete, contractors install the stainless steel cladding panels that create the surface form of the 30 m tall Kelpies. From the start, The Kelpies were designed for ease of erection, enabling assembly with standard mobile cranes and ‘cherry pickers’ with no need for scaffolding. Even the lifting points and sling lengths had been calculated for each frame of the structure, so that the frame hung from the crane at the right orientation for easy connection © SH Structures 20 INGENIA INGENIA ISSUE 60 SEPTEMBER 2014 21 THE FALKIRK KELPIES SOCIETY A file was created that reproduced each plate by recording the coordinates of three points on its surface. This approximately located each plate, and allowed its inclination in three dimensions to be calculated accurately, which was needed for the manipulation to follow With one much smaller and bend them to the shape of the simpler exception, he had always underlying structure. This required built his sculptures himself, with careful design of the support his welding kit in his workshop, structure, both to locate the bolt without help (or interference) positions in the right place to from others. Now he had to achieve the required curvature, create two major structures, and to take the bending loads. each as high as a 10-storey The engineers’ idea of merging building, with a design that the plates and then pulling the could be fabricated and skin onto the outer frame made assembled at an acceptable cost. Andy nervous. He feared it would This was an altogether different lead to unacceptable steps and challenge, and one where he discrepancies on the surface. needed engineering help. For Sketches passed to and fro, but the engineers, our challenge had when his questions were to be met while retaining the answered in full he supported the sculptor’s vision. Thus began a proposal, commenting that a little period of collaboration and unevenness would actually lead to learning for all involved, a better-looking figures. process that would take us all And so a process was outside of our comfort zones. developed for converting Andy’s The first creative stages were This CAD design was made for The Kelpies bid tender stage. It is coloured in to show potential constructors how the maquettes into a buildable structure would be broken down into separate components and how large individual pieces would be © Atkins for Andy alone. He subtly shifted The sculptor, Andy Scott, with the 1:10 scale maquettes that helped secure lottery funding. They were made by welding design. The individual plates were the brief away from mythological together hundreds of small steel plates on a temporary internal skeleton © James Stewart Photography projected onto the smoothed kelpies towards the heavy horses than smooth surface for the 3D-surface computer model of would be prohibitive. A solution solid surface model, and then – the Clydesdales, Shires and frame. The mosaic effect created DESIGN INITIATIVES Choice of material was also an stainless steel. The Kelpies to be produced, which was to replace between nine and examined by eye to see how the Percherons – which had been by the flow of the plates and the area where he was happy to Our first proposal was purely Atkins scanned Andy’s helped at a later stage when the twelve adjacent plates with a plates might best be grouped, the powerhouses of industry view through the openings defer to the engineers, pragmatic. At full scale, the open second set of 1:10 scale plates needed to be made. single sheet of 6mm-thick flat bearing in mind the size of the and agriculture in the Falkirk/ captured the horses as if in accepting that a stainless steel steel surface would be an maquettes to produce a 3D The most difficult and steel plate, laser-profiled to profiling beds on which the Grangemouth area, and would motion. surface supported by a structure computer model of the surface. invitation to adventurous visitors intractable engineering problem represent the separate sheets, panels would be cut, the once have pulled the boats These helped secure the in painted carbon steel would A file was created that was how to replicate the surface, and then bent in three to climb the structure, so the maximum size of sections for along the Forth and Clyde canal. lottery funding which enabled have a much longer life than the reproduced each plate by with its more than 9,100 separate dimensions to approximate the engineers suggested that the transport to site, and the layout of His initial sketches, using two the whole Helix park galvanised steel he usually recording the coordinates of plates, at 10 times the size of the changes in angle between the supporting structure. The bottom 3m should be a smooth Clydesdale horses from Glasgow development to go ahead, and worked with. Another practical three points on its surface. This maquettes. The construction adjacent plates. plates in each group were joined surface. Andy welcomed the City Council as models, were Andy was then commissioned to matter settled an important approximately located each plate, workload would be huge: a But how to avoid the costs to create an ‘ideal’ panel, smoothly change, recognising that the developed into small-scale clay build a second set of 1:10 surface detail: concern about and allowed its inclination in massive supporting structure and complications of shop- curved in three dimensions and smoothing actually helped models, and then a pair of 1:10 maquettes, exactly as he wanted the effect of glare on motorists three dimensions to be calculated would be needed that would bending 959 sheets of steel in profiled to represent the visually with the transition scale maquettes, created by them to appear. Now came the on the adjacent M9 motorway accurately, which was needed for compromise the flow of light three dimensions? The answer individual plates. Then the hand-welding individually cut period of collaboration and between the solid foundations led the engineers to the manipulation to follow. It also through the skin, and early was to erect the plates as flat anticipated support points were rectangular plates onto a wire compromise. and the perforated areas above. recommend a milled rather allowed a smooth, solid estimates suggested the cost sheets, and then use bolts to marked. 22 INGENIA INGENIA ISSUE 60 SEPTEMBER 2014 23 THE FALKIRK KELPIES SOCIETY Further software was used to The biggest advantage of using would be partly visible through over Andy’s books on horses’ trusses, interconnected by flatten the panel, producing the huck bolts was that they perforations in the skin, so it anatomy to gain an bracing frames to form an exact shape for cutting out allowed engineers to cope with had to look right from the understanding of the natural efficient and stiff primary during manufacture. A further the relatively large gaps outside. muscle form and look at how structure. This supports a routine was then run, taking the between the panel and the Standard engineering this could feed into the steel secondary frame following the flat panel as it would be on brackets underneath before the structures are robust and design. These studies led to the internal surface of the skin, arrival on site, and pulling it tightening process. The panel geometric, but Andy wanted back under the mane and the 1:100 scale models used for wind tunnel testing © Atkins consisting of cladding rails back to the required shape could now be pulled using soft something that captured the natural bulge under the throat carrying the brackets which using the identified support being used to hide some of the strops to a location close to the form of the horse, recognising pick up the thousands of points. that there are no straight lines additional supporting structure. required shape, and then the fixing points for the stainless At this stage, we and Andy in nature.