The diagrid at the Macquarie Bank build ing at One Shelley Street, King Street Wharf in Sydney, was used for a number of reasons. Initially it was used to transfer the load of the build ing toward the perimeter, which meant the number of columns within the net lettable area would be significantly reduced as it transferred the columns to the outside of the building.
The diagrid is made up of three elements — structural steel, a fire rated board and aluminium cladding. The base structure, which was galvanised steel supplied by Bluescope Steel, comprises three main sections — the starter piece; leg pieces, which were inserted into the starter pieces; and nodes, which connected each interlocking section.
“The diagrid starts off as a flat plate around 70 mm thick 450 mpa steel, which basically gets run through a big plant at a Port Kembla steel mill, which pushes out a whole heap of plates which then gets cut into strips which are 300-odd mm in size,” says Andrew Steventon and Patrick Murphy, the two project managers at the project at Brookfield Multiplex.
The outside dimension of the columns were 312 mm by 327 mm, which were welded into an I-beam. That I-beam then either had plates welded onto the end of it to create legs or were fabricated into nodes.
The diagrid is made up of over 320 node and around 650 legs. Each one of those was slightly different in size and all individual pieces. “It looks like a bit of a mechano set but it’s actually not. It’s a very specific puzzle and every piece had to be put installed in the right sequence,” Steventon says.
Columns and nodes ranged from 70 mm thick down to a 30 mm thick plate and in some areas, universal columns sections were used and every welded joint on the diagrid was weld tested.
Initially the raw steel was fabricated and galvanised before each piece was delivered to the site. The individual pieces were then bolted together on- site and installed. Brookfield Multiplex co-ordinated Allsystems, who placed a Promat fire rated board around the steel to ensure fire engineering was maintained. On top of that, aluminium cladding by G.James was placed around the outside, which was extruded aluminium components which were also powder-coated.
Steventon and Murphy worked closely with G.James, with G.James specifically developing many specific products for the project to ensure there were no long-term issues. “Because this structure penetrates the façade in so many places, we had to work very closely with G.James in relation to the cladding and the penetrations because if the diagrid deflected or moved too much, it could then break the glass or it could damage the façade. It could also then potentially damage the cladding itself,” Steventon says.
The diagrid penetrates the façade at every intersection through the curtain wall to the floor beams which then hold up the concrete floor. This presented a potential issue with waterproofing, so every sub penetration was specifically designed, engineered and tested to avoid leaking.
Steventon says there were no on-site issues during installation, with regular reviewing and monitoring as the diagrid was installed.
The diagrid is the first in Australia, with similar types of systems used overseas at buildings such as the Gherkin in London and other buildings in New York and Dubai. Although these overseas examples had the potential to provide some insight into how install the system, Steventon says the international examples were different in many ways.
“The engineering principles were the same but the actual constructability of them was very different. For example, one’s made out of concrete, and our diagrid is set outside the façade of the building. The other diagrids are integrated into the curtain wall, so the diagrid is installed and then you fill the holes in the curtain wall panels.” The diagrid at One Shelley Street is set off the façade by around a 150 mm gap between the glass and the inside edge of the diagrid.
Steventon says: “The diagrid is an engineering feat as far as the amount of engineering that goes into it. As well as being an engineering feat, it also obviously provides a significant architectural advantage for the building.”
Brookfield Multiplex was the developer, builder and facility managers. Arup was responsi ble for all the engineering at the project and Fitzpatrick + Partners was the architects.
