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Cutty Sark Pavilion

Cutting edge engineering expertise played a key role in the construction of London’s Cutty Sark Pavilion. A timber and fabric gridshell built as a temporary pavilion and exhibition space in London to promote the historic sailing ship, the Cutty Sark, showcases the cutting edge engineering expertise involved in combining the two materials in construction projects.

The pavilion evokes a bygone era of sailing with its nautical design theme reminiscent of sails, masts and the famed ship’s rigging. It was built to remain on its Greenwich site overlooking the river Thames during the Cutty Sark’s restoration and while a permanent visitor’s centre was being built.

Structural engineer, Toby Mason, who was working as an associate director for London-based engineering firm, David Dexter Associates, at the time, was enlisted to provide specialist advice on the complex geometrical structure’s form and its construction. The pavilion was designed by Youmeheshe Architects.

Mr Mason has since moved to New Zealand and is now an Associate with Hastings-based consultant engineers, LHT Design.

“We are looking for opportunities to employ some of the technologies in timber and fabric construction we used in the Cutty Sark Pavilion project here in New Zealand and things are starting to happen,” he says.

He says the Cutty Sark Pavilion – erected next door to a dry dock where the Cutty Sark was being restored – was created to inform the public about the conservation project. “The pavilion was to house some of the ships memorabilia and also formed an interactive media centre. The iconic form of the structure was used to create interest and draw in passersby.”

The project’s client, The Cutty Sark Trust, wanted the pavilion to be cost effective, elegant and iconic enough to succeed as a tourist attraction. It also had to be capable of being relocated at the end of its life.

Other project requirements were to meet high performance standards for durability, space requirements, usability for exhibitors, accessibility for the public as well as be robust in structure.

Mr Mason says the use of tensile fabric, wooden struts and cable bracing for the structure “were obvious choices echoing the materials used in the boat’s original construction and in particular its sails and rigging.”

The biggest challenge facing the project team was that the pavilion had to be built within a restricted budget and a tight construction programme. “The project went from concept to construction in just three months to meet a fixed restoration programme,” says Mr Mason.

With a small budget of £450,000, “the use of timber and fabric proved the right choice in meeting this constraint”.

Struts
“Rather than using a rational structural form the architect wanted the geometry to be warped, Mr Mason says. “It proved tricky to get the fabric to align with the hexagonal timber framework below.”

The struts were made from 180mm x 180mm laminated Douglas Fir with the sections sized to provide sufficient residual capacity after a 30 minute fire rating.

The irregular nature of the geometrical structure meant every strut had to be a different length.

“In the main, the struts were working relatively hard with the effective lengths in excess of 6m,” he says. “However, using standardised components for a regular geometry means there is some over capacity in some locations, but these were kept to a minimum.  Recessed lighting strips were located on elements where we had additional capacity.”

Originally the plan was to clamp the fabric to the struts. However, the torsional stresses on the struts became the limiting factor. The clamp node detail provided the separation required and tolerance with the skin. It also lightened the form.

Node Connectors
In collaboration with the timber manufacturer the design team devised a bespoke pure compression timber node detail made from laminated wood. However, as each node was unique, the lengthy time it took to CNC the joints prevented them from using this solution in the end.

Instead, Toby Mason created a cast spherical metal node detail to provide a simpler way of accommodating the geometry and connecting the timber elements. “This solution had the added advantage of echoing the cannon balls on the Cutty Sark,” he says.

The ends of each strut were tapered to provide a more elegant connection with the spherical nodes. Epoxy dowelled threaded rods were used to form the connection.

Ply Side Panels
Low level panels along the side walls were built using marine grade ply. “The folded nature of these provided geometrically stiff elements that form the anchorage to the slab,’ he says. “They also provided a degree of robustness to the low level perimeter that was more prone to accidental damage.”

Other technical challenges 
Mr Mason says as with every timber structure the detailing work on the connections need to be considered at the outset and can end up defining the element sizes. “Therefore this formed a primary consideration in the design.”

Due to the structure’s complex and irregular geometry a sophisticated fabric analysis software was used to generate the form and analyse the component forces. The software also helped to optimise the form to minimise the out of balance forces.

Another challenge was the poor quality of the ground where the pavilion was to be erected.
“The original concept was to have piles and an elevated timber sub floor. However when we turned up on site it became apparent that there was a series of old house basements under the site. We therefore switched to using a thin RC slab that could be removed at the end of the pavilion’s life.”

After serving as a temporary space the Cutty Sark Pavilion will be dismantled and re-erected elsewhere; possibly as a remote classroom, museum, or exhibition space dedicated to telling the tale of Cutty Sark to audiences around the world.