A bustling urban setting. A heritage-listed church. This new addition to Sydney’s skyline required some creative thinking to get off the ground.
St Stephen’s Uniting Church is a 1930s sandstone building constructed in the interwar gothic style. Standing on Macquarie Street just north of Sydney’s Martin Place, directly across the road from the State Parliament, it is a part of the city’s history.
So much so that, in 2004, it was heritage-listed by the New South Wales Government Office of Environment and Heritage.
“It is part of a group of high quality and historic buildings lining Macquarie Street and contributing to that historic precinct,” the Office notes in its statement of significance for the church.
Given that history, building a 21st-century skyscraper right next door was to be no straightforward matter. Replacing a 1970s-era office building, the 137 m tall tower that would become 60 Martin Place was one that a lot of people were concerned needed to be worthy of the esteemed structural company it would keep.
“The striking, curved façade offers breathing room to St Stephen’s Church next door, a heritage building typical of this pocket of Sydney,” the architectural firm Hassell boasted of its work on the building.
“Through a unique cantilever design, the tower’s north face extends out eight metres above the 1930s-era stone church.”
Achieving that design, however, meant coordinating between a number of different engineers, as well as with architects, council regulators and the client, property developer Investa.
Structural engineering was overseen by Enstruct, with Surface Design taking care of the façade, Norman Disney and Young doing the mechanical engineering for energy performance and Arup taking the lead on environmentally sustainable design and specialist lighting.
Laying the groundwork
Tim Boulton, a structural engineer and Director at Enstruct, said that getting the project right took a lot of planning.
“These major CBD high-rise projects have a very, very long gestation,” he told create.
“It can be several years of getting the planning into place, and then you’ve got a few years to construct it.”
Enstruct’s involvement with 60 Martin Place began before a design had even been chosen for the site. One of the first challenges encountered by the engineering team was a council planning requirement that would have limited the 33-storey building to a much shorter maximum height than what it stands at today.
So negotiations for a taller building started even before the first stage of the development application.
“The project team worked through a process with Sydney City Council whereby it was demonstrated that the existing buildings exceeded current overshadowing planning requirements,” Boulton said.
“The project team achieved approval from council to build a structure that maintained overshadowing in Martin Place; it didn’t make it any worse than the previous building that was being demolished.”
With that argument won, the Enstruct team maintained its involvement as the project entered the design competition phase.
“We continued working with Hassell through the design competition, as they were one of the entrants,” Boulton said.
“It was an open and collaborative relationship between minds for these design competitions. You do get the best — for the clients, the city, and everyone involved.”
Over the edge
The most immediately striking thing about Hassell’s winning entry was the cantilevered design, which curves gracefully and helps the building complement its urban setting as well as expanding the available interior space.
“A big part of the development that Investa put together was negotiating with council and St Stephen’s church next door to utilise the airspace next to the heritage-listed St Stephen’s church. That allowed the building that we developed to cantilever over the church,” Boulton said.
“Structure was always playing a critical role to utilise and make best use of the space available to make the most of the development opportunity.”
But realising this design was no straightforward task. Martin Place is a bustling part of the city, and to make matters even more complex, a number of train lines pass just beneath the surface. Getting the trusses and steel plates in place to support the cantilever took some creativity.
“Because we cantilever over the church and we can’t have any vertical supports through the church, there’s quite a novel way of doing it to maximise the cantilever but minimise the structural costs,” Boulton explained.
“For the low rise section of the building, the floor plate cantilever over the church is achieved through increasing cantilevered floor beams, with these beams reaching their capacity for the available depth just below the mid-height of the building. To allow the cantilever to continue to increase, three 40 t steel trusses are provided at level 18 in the plantroom to provide a transfer of the tower columns along this edge”
That cantilever incrementally increases the higher the building gets, Boulton said. But at a certain point, the floorplates can’t cantilever any more. Enstruct, however, found a solution.
“That’s why we then, at level 18, introduced the steel transfer trusses, which allowed us to basically reset the primary tower column out over the boundary. And then we start the cantilever again and the floor plate continues to cantilever from there,” Boulton said.
“We’re achieving the cantilever twofold, both by cantilevering each floorplate itself from the tower column, but also through the steel transfer trusses that we have at level 18. They reset the tower column out over the boundary, which is a major transfer, because it is transferring the level 18 to level 32 loading from primary tower columns supporting that northern edge of the building.”
Best in show
It is impressive work — and impressive enough to have been recognised internationally. The Chicago-based Council on Tall Buildings and Urban Habitat (CTBUH) listed the tower in its Best Tall Building 100-199 Metres category for 2020, and also acknowledged it with a Façade Engineering Award.
Robert Moisy of Surface Design, who worked on the façade engineering, said he was very happy to have been a part of the development’s success.
“It is great that internationally the building and specifically the façade engineer has been recognised, and we are pleased to have been a key contributor to the project,” he said.
“Critically, in a project like 60 Martin Place, the client set clear goals and aspirations and allowed the team to find the best market-leading response to these key project requirements.”
One of those requirements was to ensure the overall design supported Investa’s sustainability objectives.
“Sustainability initiatives include a 6-Green Star rating, achieved through a high-performance building envelope, a partly self-shading faceted northern façade and ‘end-of-trip’ facilities to support cyclists and joggers working at 60 Martin Place,” note Helen Lochhead and Philip Oldfield of the University of New South Wales in a CTBUH research paper.
“On sustainability and aesthetic, for me, these go hand-in-hand, and relate to designing the façade,” Moisy said.
“In minimising the use of materials, the visual impact of the system is improved to allow the views beyond the façade, such as views of the city or the heritage church. This allows sustainable qualities such as cultural use and wellbeing for the users of the spaces.”