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Inside the Arup project to create printed elements for complex structures

Arup has lifted the lid on a research project that could one day mean parts of specialised structures are 3D printed.

Arup senior designer Salomé Galjaard spoke to NCE about how she saw the future role of additive manufacture in optimising complex structural geometry.

Additive manufacture, more commonly known as 3D printing, is a process by which an object is built up layer by layer using a laser to heat up and melt powdered metal to form complex geometrical shapes. Arup last year revealed it had manufactured steel nodes using the techniques.

Now it believes it has created an element 75% lighter and 50% per cent smaller than traditionally would be used to carry the same load.

Galjaard said that when Arup was working on a complex tensegrity structure - a structure in which isolated compression members are held in equilibrium by tension members, such as in the Kurilpa Bridge in Brisbane - the project was limited by the production methods available at the time. So she set up a research project to see how making the production of the 1,600 nodes with 1,200 different variations could have been more efficient.

“We have all these tools to calculate and visualise and to prove digitally with the computer that a structure could work or what it might look like, but the production methods themselves can be quite limiting in what can be achieved in the real world,” said Galjaard.

The team started two and a half years ago. Using computer aided design techniques she said they took the traditional node, which comprised a tube cut to length, with hand welded lugs, and tried to reduce the weight and amount of material needed using the advanced manufacturing techniques.

The first iteration still looked like the original she said because of the design decisions they had taken. But it could still be optimised.

“So what we did after the first design was to go through the design process again implementing all of the things we learnt to see how far we could take it, really making the most of additive manufacturing,” said Galjaard.

She said the first iteration kept the lugs, which allowed the struts to be connected to the nodes with fork and pin connections in the same place but that took a lot of material to produce.

“All of the forces go through one point along the centre line; providing all this space for the pin and fork connections forced us to bring those points away from the centreline,” said Galjaard. “So in our second try we thought, instead of looking at these elements in isolation, [which is] really limiting our optimisation, why don’t we try looking at the structure as a whole.”

Using just a pen and paper, she said they looked at ways of making the nodes more complex as the production was not an issue. “We wanted to include the functionality of the fork, pin and spanner in these nodes,” she said.

The team managed to condense down the node, so that the cable simply passed through the hole and was terminated by a nut on the other side. The nut also allowed the cable to be tensioned in the same way a turnbuckle would on the traditional connection.

“The only thing we had to be sure of is that we could always reach the nuts so we could always increase or decrease the tension in the cables and we had space for the end length of cable inside the node,” she said. “We eliminated 15,000 elements from the design, and that’s only the pin and fork and spanner. The node itself is now 75% lighter.”

The parts have not yet been tested for strength, but they have been tested for material specification. The team is now looking at new opportunities to see how other projects could benefit from this technology.

Galjaard stressed that these nodes were tailored for the particular project and she didn’t see this type of technology taking over for traditional methods of construction, but that there was a place for this new technology.

“It’s quite specific, but it’s the opening of your mind for the different possibilities – it’s a different way of thinking required than we were used to before,” she said.

 

 

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