A simple plan
Tony Lavorato, Design Director, Structural from Aurecon will be presenting on 5 Martin Place, Sydney – Challenging the Normal at 3.30pm on Thursday 27 September, 2018 at ASEC.
In this article (originally featured in the June 2018 edition of Engineers Australia’s create magazine) Tony talks about how the key to being innovative is to come up with the simplest solution possible.
Credit: create magazine
While new technology and new materials are opening up new possibilities in the world of structural engineering, Tony Lavorato says innovation comes from understanding the basics. By Christopher Connolly.
It’s easy to fall into the trap sometimes of thinking that a complex problem is going to need a complex solution. And sometimes it does. But the key to being innovative, according to Aurecon Design Director Tony Lavorato, is to come up with the simplest solution possible.
“The structural design has to be something that a designer can explain to someone very simply on a sheet of paper, in 60 seconds,” he says.
“You should be able to describe how a wind load at the top of a building gets translated through the structure to the ground, how the skin of the building is supported and how those loads then get translated, how it all works in terms of deflections and serviceability. That all needs to be described very simply, and if it is simple, you can then maintain that throughout the design process.”
He says the role of design director is a new one in the company, one of ten, covering everything from tunnels to ports to manufacturing. These design directors are “custodians of the design” from start to finish.
“My role is to really make sure that clients can access our key thinkers to get that original concept right. And I think that’s where, as engineers, we need to really differentiate ourselves,” he says.
“We see clients coming to us initially to ask us the questions, and we can channel that design back to them, mainly in terms of site selection or how they’re going to build it, whether they have time constraints. Now, when you build in the city, there are so many constraints. The method of construction can influence the design very much. So at that initial design stage, you need to take that into account. Physically, what trucks can actually land there? How much space do they have to build it? And then reflect that in design.”
The Money Box
A recent project he highlights is in Sydney’s CBD. On the corner of Pitt Street and Martin Place is a historic Commonwealth Bank building, affectionately referred to as the ‘Money Box’ building because its design has been used as the basis for Commonwealth Bank money boxes for almost 100 years.
Lavorato says it was originally built in 1916 with additions in 1933 and 1960, although the latter addition “wasn’t really sympathetic to the heritage nature of the site”. In the 1990’s, after a failed move to replace the 1960 addition with a tall building, Sydney City Council put some controls on the site, including a height limit, a setback from Martin Place, and restrictions on the 1916 and 1933 components so they couldn’t be altered or used to support any load.
The building owners were anxious to increase the net lettable area of the site and asked builder Grocon, supported by Aurecon, to investigate the idea of a cantilever structure over the old building which met all the Council conditions on the site.
“So we had to cantilever the building some 22 metres, or 11 levels, over the old Commonwealth Bank building, but couldn’t actually support it,” says Lavorato.
“The actual design concept was very simple, a strut and tie. But the large forces that were involved and getting those forces from one element to the other where there were enormous tensile forces going down to another element which had tremendous compressive forces through the nodes was the most complex. How you got those nodes to work, how they work within the space that we were given, and how they could be detailed so that they could be constructed, as well.”
In order to transfer these loads, he had V-shaped braces on all four sides of the tower which were incorporated into the visual design of the building. That meant they had to be aesthetic as well. The angles involved all had to be the same, despite the fact that the struts on the southern face came down from level 14 but on the northern face they were strutted down from level 11, requiring
“The collaboration between the structural engineer and the architect is probably one of the closest relationships in building,” he says.
“We like to get involved as early as possible. There was an alternative scheme that had been developed for this building where it had, I think, a much more complex truss system. We then worked with the architect on an alternative scheme, making sure it worked within their architectural design and how they wanted the building to look. And in this case, it was quite successful.”
And to make the task even more complicated, the early stages of the cantilever section had to be built supported by hydraulic jacks until the structure as a whole could support its own weight. But the act of removing these jacks would cause movement of this section as the loads were redistributed, so they had to try to predict what this movement was likely to be so that they could build it in such a way that it came out level after settling. The problem here was, while the structural design followed basic laws of physics and the loads involved were well understood, the material properties of the concrete were not.
“In normal engineering, you look at a concrete strength, and it’s always a minimum,” he says. “So when you specify 40 MPa concrete, you would expect to actually get slightly higher strengths delivered. In our case, we wanted to make sure that the building deflected into a horizontal vertical alignment. So when we’re looking at the material properties, we’re looking at a lower bound and an upper bound. If we overpredicted the movement and released the jacks, then it would’ve been up too high. If we underpredicted, it would come down too far.”
For this reason, the day they removed the jacks was very stressful as they lowered them in 5 mm increments, checking that it was deflecting at the rate expected and there were no signs of any structural problems. Finally, they could see daylight between the jacks and the underside of the cantilever and the final deflection was within a millimetre of their prediction.
“I’ve done a lot of underpinning of buildings where we remove large amounts of structure including foundations underneath buildings and hold them up while they’re constructing,” he says.
“What always amazes me is how resilient buildings are and how it seems to find a different load path and there’s a great resilience in them. They tend to redistribute loads within its structure. So I tend to think that we overpredict the movement a little bit.”
Lavorato’s path to engineering was slightly unusual. He knew he was interested in science but wasn’t sure exactly what he wanted to do, so just enrolled in a range of first year science subjects at the University of Sydney. In his vacations, he worked on building sites as a labourer and, on one particular site at Parramatta, he found an engineer who was happy to answer all his questions about what they were doing.
“I was quite curious. Why was this reinforcement going in here? Why was that concrete being poured in that way?” he says.
“This engineer took the time to actually explain it to me when he visited the site doing inspections. He was very generous with his time. What was fascinating was that, 20 times every day someone asked, ‘Can we do this?’ and the answer was, ‘Well, you better check with the engineer’. So it seemed to me that he was a person that everyone looked up to, who was critical for the day to day operations of how that building was built. And it really encouraged me to think about engineering. So when I came back from first year, I immediately started second year structural engineering.”
At the end of his degree, he was keen to stay in design rather than work directly for construction companies as a site engineer, like many of his classmates were doing. So he got a job in the then Department of Housing and Construction, working on projects for the Department of Defence, Telstra, Reserve Bank, etc. However, it soon became obvious this work was being outsourced to private consultants, so that’s where he turned, working first for Kinhill Engineers, then Meinhardt and, for the past seven years, Aurecon.
One of his favourite projects was one of the smallest. The University of Notre Dame was building a medical school opposite St Vincent’s Hospital in Darlinghurst. On the site was the Sacred Heart Church, which had been expanded in the 1960s but was being reduced back to its original size to provide room for the new faculty.
“At the back of the 1960s expansion, there was a big concrete shell structure behind the altar. with a magnificent mosaic, The Risen Christ, by Enrico Gaudenzi,” he says.
“It was huge. I think it was 10 metres high and about four or five metres wide. What they discovered is a lot of the tiles had been formed in the Vatican’s studios. So there was a great deal of heritage significance on that particular mosaic. They wanted to somehow lift this bit of the altar, bring it across, and lower it down. But because it was on a thin shell on a curved element, we were concerned that if you lifted it and it moved even slightly, it would pop the tiles.”
So, after a lot of research and planning, they decided to encapsulate the concrete shell, bring in a crane to put it under tension while they cut the base with diamond saws before moving it gingerly to its new location within the old church.
“It wasn’t a big project, but it was one where you could make a difference,” he says. “It took a lot of planning, and a lot of engineering. And we didn’t know until the day whether it was going to be successful or not. It’s the one that I do feel is a great accomplishment.”
The next challenge on his plate also involves heritage considerations. Earlier this year, the NSW Government announced that Laing O’Rourke would undertake works at Sydney’s Central Station to build the platforms and associated infrastructure for the new metro line connecting the northwestern metro line with the city and Bankstown. Aurecon and joint venture partners GHD will work with Laing O’Rourke on the project, which will include two platforms around 27 m below the current suburban platforms, and a new tunnel providing access to the platforms.
“One of the key challenges on the project will be constructing the 19 m wide underground walk from the eastern entrance in Chalmers Street through to the metro box, just a couple of metres below the operating suburban platforms, which operate pretty much seven days a week, except four or five hours a night,” he says.
“There’s heritage across all of Central Station, and certainly the suburban lines have a lot of heritage structure. It also incorporates the works around the northern entrance, which has some heritage works around the electrical building as well as how that worked with the structure. So there’s underpinning of some of these heritage works, as well, that’s involved.”
But it is challenges such as these that keep his job interesting.
“Every day, there are new challenges, and every year, there are new projects that are challenging,” he says.
“But it’s where you make a difference that it’s most satisfying, where your design has enabled the client to create something, some value that they didn’t have at the beginning of the process.”