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The challenge | The teams | The designs | The test | The demolition
This week the teams have to build an architectural marvel: a dome. Their hemispherical designs must contain a small door and may not have any internal support columns. No less than 6 metres wide and 3 metres high, the structures have to be strong and waterproof as they will be tested by being blasted with 14,000 litres of high pressure water for two minutes. A single drop falling inside the dome will mean failure. As ever, the team with the best design gets first choice of the weapons of destruction, then it's a race to render the opposition's construction to rubble. Let the games begin.
Peter Chong: Engineer
Peter works for the same company as the rest of the team, Peter Brett Associates, and is more used to managing the construction of bridges. His cool style makes him the leader.
Robert Corney: Builder
Mountaineering and ice-climbing are the favourite hobbies of action man Robert. A top engineer and builder, he's used to having Peter as his boss and promises to keep him in line.
James Skilton: Demolition
Hands on James likes the idea of explosives. Unfortunately, for this show he can only choose the pulverizer, impact breaker or wrecking ball. Still, there's sure to be enough destructive capacity available for live-wire James.
James Hayes: Engineer
Involved in the building industry from an early age, James's experience ranges from barn conversions to bay side apartments. A devoted rugby fan, this Welshman can't wait to try out his skills on Demolition Day.
Alan Williams: Builder
In his 30 years of construction experience, Alan's career has taken him from craftsman to running the company. A shooting and fishing fan in his spare time, he still loves his job and doesn't think anything will faze the team.
Paul Flynn: Demolition
Paul has 15 years' construction industry experience and is just as happy building houses as knocking them down. He says 'In Wales there's a multi-skilled approach to building.' Let's hope that includes building domes.
Dome structures are used to cover large areas with a roof without the need for internal support columns. However, a price is paid for this advantage. The structure has to maintain constant stresses throughout, as the design tries to deal with distributing the weight of the roof in several directions at once. The key is in obtaining a geometrically exact circle for the base and maintaining accuracy in the upright supports built into the structure itself. If it is not carefully built it can twist and collapse.
The Arch Angels create a ring-beam out of plastic piping and hold this in place with concrete-filled car tyres. The flexible pipe is also used for uprights, and supporting rings are tied in place with rope and tape. This makes the structure incredibly flexible. The top of the dome is given a hat coated in geotextile and bubble wrap for waterproofing.
The Killer Wales decide to construct a concrete foundation ring with steel reinforcing bars sticking up 1 metre from the top. Plastic piping is threaded on to the bars and tied at the top of the dome with a plywood 'keystone'. Without time to create the cavity wall they would like, the final design has plywood cladding which is sealed with expanding foam.
For the test, Demolition Day has brought in judge Tanya Ross and the fire brigade. Tanya was responsible for design management of the Millennium Dome in London (which is actually not a dome but a hemispherical tensile cap) so she's experienced in such futuristic constructions. The fire brigade have brought with them 14,000 litres of water and a high pressure hose powerful enough to empty a fire tender in 15 minutes. That's got to mean trouble for the teams.
The Killer Wales get the water treatment first. Initially holding up well, their weak point of the 'keystone' starts to let the water in. Inside the dome, cameras reveal the shower from the ceiling and judge Tanya, observing from inside with a brolly, has to fail their dome.
Next up the Arch Angels get a soaking. Their ill-fitting rain hat just doesn't provide enough waterproofing and judge Tanya is glad she has taken her umbrella. She fails this team, too.
So neither team passes the test. But which one impressed Tanya the most? The teams have to wait for Demolition Day to find out what Tanya thinks.
Judge Tanya says her favourite design is the one built by the Killer Wales because it has the most accurate and shapely construction. That means that Paul Flynn gets first choice of the demolition tools.
Paul makes a tactical move and chooses the pulverizer so that it's denied to the opposition. 'That thing could cause our dome real trouble,' he says. James Skilton is devastated: 'I had my eye on that!' he says. He chooses the impact breaker as second best. This week the demolition line is set to a new tough level. No debris can remain more than 75cm above ground.
The air horn sends the machines into action. With an aggressive punch the pulverizer smashes the Arch Angels' hat inside out and flings it to the floor. But soon the springy rope and tape joints of their main dome start to make fun of the machine: they keep bouncing back.
Meanwhile the Arch Angels punch through the Killer Wales' structure and rip the sides to pieces. Soon both teams resort to tracking their machines over the site to level the remains. The last steel reinforcing bar falls over and the Arch Angels just manage to win. To rub salt into the wound, the Arch Angels dome bounces a few pipes back up at the Killer Wales just after the claxon sounds.
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