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The Challenge | The teams | The designs | The test | The demolition
The Demolition Day arena is set: two stone pillars stand 10 feet (3 metres) high in each team's area. The challenge this week is to to span the 30-foot (9-metre) gap between them with a bridge . For the test a 2 tonne car will be driven over the bridge, which must show no signs of structural failure. The team with the most successful design will have first choice of the demolition tools. Then it's hell for leather as each team tries to smash their way to the final. The challengers will need teamwork to face the three days of building with only limited materials that are ahead of them.
Dave Barr: Engineer
Dave worked on the 117-metre long Forton Lake Opening Bridge at Gosport so he knows a thing or two about bridges. He's also very competitive and counts bungee jumping and parachuting among his hobbies.
Lewis Parker: Builder
Lewis is a qualified civil engineer and currently works as a research student at Southampton University's Construction Research Group. Before that he was a site engineer so he knows all there is to know about building sites.
David Brown: Demolition
Dave 'the brains' is a lecturer at Southampton University. In the past he has built six bridges and is also a DIY addict. He's constructed enough but can he knock them down?
Glen Kerr: Engineer
Glen is a qualified structural engineer who has worked on large exhibitions and museums. He's also Maxine's boss where they both work at Taylor & Boyd consulting engineers.
Maxine Boyd: Builder
Maxine has built a 10-storey office block in the centre of Belfast so she knows how to build big. She's also one for thrills, and has five parachute jumps under her belt. Will she come up with a big exciting bridge? Let's hope so.
Dave Horbury: Demolition
Dave has been destroying things for over 26 years. His biggest job was demolishing a huge fertiliser plant using explosives. But can he handle the Demolition Day machines with as much success?
There are loads of ways of designing bridges but just a few fundamental types of bridge: beam, suspension and arch. The key is to match the compression experienced on the surface of the bridge with tension from underneath. For ideal performance the structure should be stiff enough to withstand downward compression with little distortion along the span.
With the materials at hand, both teams come up with considered designs. The Mortarboards base their structure on a composite beam. This is made up of a latticed, studded, timber base to support large polystyrene blocks. These are then sandwiched by adding piping and plywood on the top. The sides are then strengthened with plywood sheeting. With a flare for design, The Mortarboards include additional plastic pipe arches along each side that incorporate suspension cables.
Shear Force opt for a super-strong timber design. Three long triangle-framed trusses are bound alongside each other with timber 'X' members. The whole lot is then threaded along its length with pipes, and clad in plywood. This monster bridge only just fits on to the stone pillars.
The Mortarboards
Shear Force
The judge for this week is Ian Hunt, a highly qualified civil engineer who specialises in bridges. He's built everything from log bridges in the Far East to the award-winning and forward-thinking Gateshead Millennium Bridge. 'Performance is number one here,' he says. To measure it he uses a deflection meter, which will measure how far the bridges move in the centre when a 2-tonne car rolls over them. Of course, driving a car quickly over a bridge makes the test easy, so each car will stop in the middle of the bridge for 60 seconds. Can the teams and their bridges take the strain?
The Mortarboards watch as the car rolls on. Their beam structure takes the compression well and judge Ian registers only 10mm of movement in the centre of the 30-foot span. The bridge has passed its test.
Shear Force's Maxine says: 'We're very confident,' as, with a creaking of timber, the car rolls on and stops in the centre of the bridge. Only 5mm of movement is detected. Another success.
So both teams have built a working bridge but which is the toughest and which one impressed the judge the most?
After struggling with the decision, and remarking how extremely close the competition was, judge Ian announces that Shear Force are the winners of the test because their bridge showed the least deflection. That means that Dave Horbury gets first choice from the demolition tools.
Not counting the stone pillars, the first team to smash their opponents structure to under 1 metre off the ground wins the competition. After looking at each others' structures, Shear Force choOse the PD15 Steel Shears. David Brown from The Mortarboards goes for the Pulverizer.
At the sound of the alarm, Shear Force go charging in. They're using the shears to tackle the plastic pipe arches on the Mortarboards bridge. Little do they know that these arches have little structural significance. Meanwhile David Brown directs the Pulverizer to rock the delicately-perched Shear Force structure and it snaps in two under the pressure. But then disaster: bad communications mean that their machine stops work.
Just as this happens, Shear Force realise that they have been wasting time on the plastic arches, so they get to work on the main structure. Soon that too is in pieces on the ground. Now the race is truly on. With their machine working again, Bad communication continues for The Mortarboards: their tool is piling the material up instead of levelling it. Shear Force continue to flatten their site but the plastic pipe refuses to lie on the ground. Finally The Mortarboards clinch the show by a whisker! A solitary erect pipe has beaten Shear Force.
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