Price & Myers’ Hy-Pavilion

Tim Lucas, a partner at Price & Myers and founder of its Geometrics team, had always wanted to design a pavilion. His ambition was realised when, as a committee member for the London Festival of Architecture, he had the idea of designing a pavilion that was formed from two intersecting hyperbolic paraboloids.

“Hyperbolic paraboloid is a really beautiful piece of geometry that allows complex structures to be achieved in a simple way,” says Lucas. “Geometry and maths are used to resolve its form which results in a very pure solution”.

The Hy-Pavilion, named after its shape, is 9m tall and provides a 360-degree stage and shelter for events, and has been built by arranging the two intersecting hyperbolic paraboloids at 90 degrees to each other.

A hyperbolic paraboloid is a complex curved shape formed from straight line elements – in this case formed from tightened bungee ropes. The double-ruled form means that there are two straight lines passing through any one point on the surface of the structure.

Key to making this structure possible has been the material used. Lucas specified Kerto-engineered timber, which combines strength with relative lightness, compared, say, with steel, making it easier to erect the pavilion.

The pavilion also features a fabric made by Millimetre, that has been stretched across the timber beams, together with the bungee ropes, used because their elasticity means that they are in effect pre-stressed.

It took about four months to design, make and assemble the different components of the structure. This process required a number of computer models to be created, together with physical models, which included a small model with a scale of around 20:1 and a larger 1:5 scale model.

The £10,000 pavilion was on show in Park Crescent for the first weekend of the London Festival of Architecture, and has since moved to Store Street where it will remain until July 4. After the festival, the Hy-Pavilion will be dismantled but will be available for hire.

The Timber Structure

The Hy-Pavilion uses eight 12m-long Kerto beams.

The straight beams have been cut to 10m and tapered at the ends with the offcuts used for benches. The appeal of Kerto timber is its strength – it is made from thin layers of timber glued together, with Lucas describing it as “jumbo plywood”.

Each beam is 75mm thick and 400mm deep in the middle. They have been varnished to protect the cut edges, and their tips have been clad in a bespoke stainless-steel plate and hinged. The hinges are a critical part of the design and make it possible for the pavilion to be erected without a crane. The tips of the beams pivot and rotate to become an X shape – each face looks like an X – and each beam is positioned at a 55-degree angle. A pivot has been fixed in the middle of each X or the point where the two beams intersect.

So that the beams can be transported on a normal-sized truck, to keep costs down, they have been cut into lengths a maximum of 6m, with steel plates used to splice them together once on site.

Four steel trays have been placed on the ground and 16 concrete paving slabs per corner have filled each tray and have been bolted down. The tip plates to each beam have been bolted to the trays and each base weighs approximately 200 kilos, providing enough ballast to ensure the pavilion won’t blow away.

A 5.8m x 5.8m cream coloured canvas sheet has been fixed about 4.5m or halfway up the pavilion and stretched from the middle of each X frame and pulled down to the tip at the bottom of each beam. Pivots and rachets fixed to the canvas tighten and secure the canvas.

Each of the hyperbolic paraboloids has two layers of bungee ropes fixed to it which range in length from 5m to 9.5m (seven different lengths have been used), each rope being 12mm in diameter. The ropes have been looped through stainless-steel hooks screwed into the timber and the ropes stretched.

The bungee ropes pull sideways against the Kerto beams, pre-stressing steel cable ties (each is 4mm in diameter), and creating a trussed structure in plan. The bungees form the hyperbolic paraboloid shape, while the canvas has its own double-curved shape to keep it taut.

Erecting the Pavilion

Tim Lucas had been grappling for some time with how the pavilion could be erected, and then when on holiday he had a eureka moment.

“I had been thinking on and off about how to articulate the pavilion and then when I was on the plane to go skiing it suddenly came to me,” he says. “It felt brilliant when I had cracked it and I was on a high for the whole weekend, but I had no access to a computer so I had to sketch my thoughts out on paper.”

Lucas’s solution involves the pavilion being built on the ground with one timber frame positioned inside the other and in a simple action like lifting a deck chair the 700-kilo pavilion is pulled upwards into position.

A crane is not used and instead two Tirfor hand winches pull the opposite corners of the pavilion together. It’s a wonderfully simple motion that enables the structure to be easily transported and erected in any location in less than a day.

A trial erection was undertaken in the contractor’s workshop in Hull just to be sure it all worked prior to the Hy-Pavilion being transported to London for the festival.

Attaching the Bungee cords

The structure uses 56 bungee cords, each 12mm in diameter. There are 14 bungee cord holes per beam, each connecting two beams. The cords have been looped through stainless-steel hooks screwed into the timber and then stretched.

From: www.bdonline.co.uk