THE 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 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 . 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

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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.

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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. So we had to look at In places, curves were FLAT PLATE SOLUTION remaining gap removed during steel skin. could accurately assess the error how to lay out the columns and compromised by using straight The details which required the most intense the bolt installation; this was Particular attention was between the ‘perfect’ smoothed members to avoid equal pieces of steel which, when collaboration between sculptor and engineers essential to the panel-pulling given to the details of ears, eyes surface and the actual shape spacing and prevent the lines of joined together, look like curves. were the horses’ manes. On Andy Scott’s first system proposed. maquettes, they were formed from many long, flat and chin, where the surface created – for each individual A huck bolt is a cross the structure beneath jarring The resulting supporting panel and between adjacent with the flow of the skin plates. structure comes in two parts. sheets cantilevered out from the surface. After curvature was greatest and the between a bolt and a rivet, preliminary discussions, this was changed on the steelwork most complex – and panels. Where necessary, the consisting of a grooved pin and The engineers and sculptor had The first is a structure based groupings were changed or the second maquettes to a structure using angled to the horses’ manes (see Flat a smooth collar. After inserting to collaborate closely, poring around twin-braced triangular support points adjusted, and the sheets. Even with the changes, two problems plate solution). the pin in the pre-drilled hole, process was repeated. A test remained. Providing sufficient support points for The design for the whole the installation tool grips the erection of a sample section was the mane structure would require an structure was refined to ensure pintail and swages (cold-forms) carried out to prove that the COLLAR unacceptably dense support structure that it could be fabricated and the collar over the grooves to system would work in practice. HEAD underneath. And the mane area was known to assembled, and was put out form a tight joint. The bolts BREAKNECK GROOVE A computer simulation which shows the initial have high, fluctuating wind loads: wind tunnel redevelopment of the mane. The mane is made up to competitive tender. The worked well, proving quick and of a series of individual large flat panels. The angles tests and computer analysis had highlighted eddy £5 million contract was won by BOLTING HORSES simple to install. between the panels provide the shape of each mane shedding off the mane elements, and peak segment steel fabricator SH Structures. Long consideration was given to pressures occurring in the mane area. the bolts holding the skin onto PIN PINTAIL The sculptor was open to ideas for different flat. However (as on the main structure), they have the structure. Besides taking the FREE-STANDING EQUISTRUCTURE By this time, the idea of using solutions, but adamant that the mane area should been laser-profiled, to create the illusion that they design loads, these bolts had to © M Meir Huck bolt holding a panel Based at Sherburn-in-Elmet in on The Kelpies © L. Tanner have a different, rougher texture than the body of are made of longer, thinner pieces of plate. be tamper-proof and – above all the sculptures as part of the lock The Kelpies. The team reverted to the design of the Uprights have also been added, welded to the North Yorkshire, SH Structures – vibration-resistant. Wind mechanism had been replaced THE HUCK BOLT mane on the 1:100 scale models, sculpted in clay outside surface to provide more texture and specialises in complex steel tunnel tests on early models and with the proposal that they This is a locking bolt that consists of a grooved pin and a collar. The and then cast in resin, which had been produced mimic the effect of using angles. structures – the type of project computer simulations of wind should be free-standing fastener is applied by inserting the pin into the prepared hole and originally as discussion tools to test ideas, as well Throughout the structure, Atkins had been which its competitors tend to loading showed large loading structures, enabling the public placing the smooth bore collar on the pin. The installation tool then as wind tunnel models. Gradually, an acceptable keen to rely on bolts for connecting elements, avoid. The firm had been from the high winds in the area, to go inside. From early work grips the pintail, which is sectioned from the rest of the bolt by a solution emerged. In the final design, the manes keeping welding to a minimum – for both approached by The Kelpies’ team but also the likelihood of eddies with the maquettes, Andy and breakneck groove. When the tool is activated, the jaws in the nose consist of several segments, each made up of a engineering and visual reasons. These angles on in 2008 to provide some input causing high fluctuating loads. Atkins had realised that the assembly pull on the pintail and the nose anvil pushes on the collar series of individual large flat panels, with angles the mane were the principal exceptions. to the budgeting of the project, The answer was borrowed from inside of the heads could be to remove any gap. Then the nose anvil starts to swage the collar between the panels providing the shape of each The use of flat plate for the mane panels the railway industry: huck bolts, works of art in their own right, and had later assembled a trial into the grooves on the pin. Continued swaging causes the collar to mane segment. meant that a very simple stand-alone supporting which are used in train and this in turn required the skin panel to test the proposal lengthen and develop pre-load. When the swaging of the collar Unlike the main structure, where the skin structure for the manes could be developed, undercarriages but rarely in internal supporting structure to to use laser-formed sheets bent into the lock-grooves is complete, the pintail separates from the pin panels are pulled and shaped round the connecting to the main structure at just two or construction, and never before be part of the sculpture. In any to shape over the frame using and the installation cycle is complete. supporting structure, the mane panels all remain three locations. by the fabricator of The Kelpies. event, the supporting structure huck bolts.

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A total of 309 tonnes of steel, 6 km of steel tubes and 34,566 individual pieces went into building the tallest equine sculpture in the world

After a prequalification process, and assembly could be made by based on, and complementary to, perfect fit on site. A computer SH Structures submitted its tender replacing these plates with Atkins’ surface model. A BIMsight program helped define the lifting for the project in January 2012, tubular steel, curved to follow building information model was points for each frame and the along with several other the surface. used to exchange information correct sling lengths, so that the fabricators. All of the bids came in The firm was given four weeks to between artist, engineer and frame would be at the right over budget and, for a while, the prove that the changes would fabricator. The model contained inclination for assembly from future of the project was in doubt. have the desired effect. As a all the design detail, but the crane. But SH Structures had suggested result, SH Structures was fabrication and assembly Erection on site was in its bid that substantial savings appointed as design-and-build drawings still needed to be remarkably straightforward, with could be made by modifying contractors, working with prepared: nearly 2,000 were no heavy cranes or complex some of the internal supporting structural engineers Sinclair eventually produced. access systems required: first the structure. Atkins’ design was for a Knight Merz (part of the Jacobs The company fabricated all of primary trusses were set in place, tubular steel triangulated frame, group). The original skin design the structure in its own then the secondary steelwork, with bracing that included a was retained, but the supporting workshops, assembled into the followed by the stainless steel series of horizontal, flat diaphragm structure was redesigned in all largest pieces which could be skin. Standard mobile cranes plates. These plates had to be tubular steel. This resulted in carried by road. The whole sufficed for all the lifting, while profiled to follow the contours of savings of around £750,000, structure was far too large to test- safe access was provided by the external skin, and stiffened, enough to ensure that the assemble before delivery, but mobile elevating work platforms, project could go ahead. which involved a lot of work, and each adjacent frame was match- or ‘cherry pickers’. All of the skin SH Structures produced its SH Structures thought that fitted to its neighbour before was added on site, most of it ‘in own 3D model of the structure significant savings in fabrication leaving the workshop, to ensure a the air’ after the structure was erected: the exceptions were the more complex sections such as around the mouth, where the skin was added at ground level before lifting into place. The whole erection process was completed in 90 days. View looking up inside one of The Kelpies showing the primary structure based The HOME arts event, in April 2014, was the international launch of The Kelpies. Andy Scott visited SH on twin braced triangular trusses, the secondary frame with cladding rails and The light and flame show was by Groupe F – the same company responsible for Structures several times during brackets, and the stainless steel plates forming the outer surface ©SH Structures the millennium show at The Eiffel Tower © fabrication, and was impressed The Helix Park, with The Kelpies as days at the seemingly by the project team’s positive its centrepiece, was opened in interminable issues of cost and BIOGRAPHIES attitude and passion for the April 2014 to international politics. He now recognises that Felicity Starr graduated from Cambridge University in 2006 and project. He feels that few people acclaim. Visitor numbers in the getting a £50 million regeneration is a senior mechanical and structural engineer with Atkins. She will appreciate the complexity first two months were 150,000 – project started in the teeth of a has worked on projects across a wide range of industrial sectors. and skill that went into the already half the number recession was a major fabrication and assembly process, predicted for the first full year. achievement in its own right; that Andy Scott is a Scottish sculptor who graduated from Glasgow or what he calls “the magic As for the sculptor, his delays and compromises were School of Art in 1986. He has, to date, completed 70 projects behind the scenes”. A total of 309 moments of doubt, the times inevitable; and that the across a wide range of disciplines in a number of countries. tonnes of steel, 6 km of steel when he nearly walked away transformation to the whole tubes and 34,566 individual from the project, came not from region has been amazing. His The author would like to thank engineer and freelance writer Hugh pieces went into building the his relationship with the greatest joy is that the people of Ferguson for his help in writing the article and Tim Burton, A test erection of one of the 6mm-thick stainless steel laser-profiled panels forming the skin of The Kelpies, to confirm that tallest equine sculpture in the engineers and fabricators, which Falkirk and Grangemouth, who the proposed method of bending the panels onto the supporting structure using huck bolts was feasible. Right: Computer SH Structures’ sales and marketing manager. simulation of the form of the pulled test panel. The red dots are the data points identifying the intended location of each world and one of the largest was excellent throughout, but live with The Kelpies every day, plate. pieces of art in the UK. from his frustration in the early appear to love them.

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