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Engineering the record breaking Lego bridge

Lego Bridge Project

The longest Lego bridge in the world has been unveiled as part of The Bridge Engineering exhibition at the ICE.

The bridge now holds the Guinness World Record for the longest Lego bridge. Spanning 16.46m between the main towers, it has taken the record from the previous attempt in Germany which spanned 14.1m.

Designer of the bridge, Aecom global long span bridge director Robin Sham, said that it was made solely from Lego and no glue was used in its construction.

“Before I really got involved, we thought about using metal wires for the cables,” he said. “But according to the rules in the Guinness Book of Records, the whole bridge must be built out of Lego with no assistance from glue or from metal wires.

“Screwing it onto the floor is not possible either as we had in mind that the exhibition was in the library [of the ICE headquarters in London] so we didn’t want to damage the floor.”

In total, it is 31m long with two side spans, a central span of 16.46m long and four 3.1m high towers. It is 0.5m wide, weighs 0.75t and uses 200,000 pieces of both Technic and ordinary Lego.

He said that at the beginning the team considered different types of bridge, but to break the record it was decided that a suspension bridge was the right solution.

“We considered a cable stayed bridge, but in the real world a suspension bridge spans further than those,” he explained.

Sham said that one of the biggest challenges was to determine the mechanical properties of the Lego.

“We didn’t know the mechanical properties of Lego bricks, so it wasn’t possible to do the design by analysis because the physical properties were unknown. Therefore we did the majority of the design by testing.”

As part of the design, the team carried out load testing of the different components, cables, hangers, deck and towers.

“We load tested the suspension cables. The whole load from the girder onto the cable and sustained a load on it for many hours and it was adequate.”

The girder which makes up the main bridge deck is composed as a truss. Sham said that initially he wanted to design it as a box girder – a third generation suspension bridge. This is where the girders are shallow and streamline like an aircraft wing. However, he said that this was too much for the Lego.

“I wanted to do the girder in the shape of the aircraft wing, but with the current state of technology with the Lego bricks, it’s not that feasible,” he said. “If you try to make it more streamline, then it has to be stronger. In the real world you can increase the strength of the steel, but the strength of the Lego bricks is already fixed.”

The two main cables which span between the towers, follow the proportions of a real suspension bridge and have a factor of safety of two.

“In normal bridges, the span to depth ration of the cables is 1:9 for suspension bridges,” he said. “Although this is a toy bridge the structural action is like a full scale suspension bridge, so it has to follow the proportions of a real bridge closely.”

The whole bridge was put together in a workshop as part of a trial assembly in Farnham. It was then taken apart and transported to Westminster before being reassembled.

The exhibition runs until April 2017.

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Readers' comments (1)

  • I new libraries had a use. :) We had a go at designing a plastic bridge - euro bridge...when the channel crossing was being bid. A tad bit bigger than this one.
    If you added a bunch of fans on one side could you get it to flutter and break up?

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