Structural Awards 2016 Shortlist Focus: Tony Lavorato discusses 5 Martin Place, a project to renovate and extend a 1916 Heritage building in Sydney, Australia. The project is shortlisted in our Commercial or Retail category.

I really enjoyed STEM subjects at school, and went on to study general science at University but wasn’t sure what career I would follow until I worked on a multi-story building site during my vacation. I was constantly amazed at how each element of the build seemed to follow on from the previous section at the same time, facilitating the next progression of the build. I was able to talk to the structural design engineer on site, who took the time out to explain how he used Maths and Physics to estimate loads and designed the structure to resist those loads - his drawings and specifications were then used by the contractor to assemble the building. I found it amazing and immediately changed course to structural engineering.

The 5 Martin Place project has been the most challenging project of my career to date. So many aspects of both the design and the construction were complex and required designs based on ‘first principles engineering’ - that is, we could not find previous instances where such a complex cantilever had been constructed over a heritage structure with so many constraints.  

The existing 1916 , 11 level, concrete encased, steel heritage structure was one of Sydney's eminent buildings and widely recognised heritage, and one of the first tall buildings to be erected in Australia. Every Australian child during the 50s, 60s and 70s was given a replica of the building as a money box by the Australian Commonwealth Bank through the public school system, so it is widely known as the “Money Box Building”. It had been significantly altered in 1968 and 1990, but the works were not done in a sympathetic manner: for instance, an atrium that flooded the interior with natural light had been filled in during the 1990 works.

Our challenge was to reinstate the atrium but also build over the top of the heritage structure - without imposing any loads or permanent modification to the existing building. We needed to design a sustainable solution to render the site economically viable, meet the rapidly advancing demands of contemporary commercial buildings, and express an appreciation of the existing heritage structure, revealing and enhancing lost elements for a new generation.

Our solution was a new building comprising a nine-storey main building constructed behind the heritage structure, surmounted by an innovative, ten-storey, cantilevered steel-frame tower. 

The cantilever tower projects 22 metres over the Money Box Building without any structural interaction, stiffened on two sides by large V-shaped braces constructed from concrete-filled steel tubes. The load of the ‘hanging’ cantilever section is transferred back to the main building’s concrete core by inverted steel trusses. The tension forces generated by the tower’s natural tilting action are restrained by steel cables, set in concrete-filled horizontal tubes at the top of every third floor. 

It was a very challenging project. In a typical building the structure is built sequentially, and at any stage even a partially built building has structural capacity to resist loads - the construction process is incremental, and loads are gradually added. On this project the main difference is the cantilevered section of the building was constructed on jacks and lowered on one day - if the building had not performed and deformed to our exact expectations, the floors would not have been level – so this had to be done perfectly. There was no plan B. 

The most exciting moment occurred during November 2014, when the jacks were lowered and the cantilever structure was engaged. It was immensely rewarding to see the successful outcome of all the hard work when the structure relaxed back into the desired position, exactly as predicted by the team’s sophisticated structural and movement analyses. 

We believed 5 Martin Place to be a world-first steel-frame structural engineering solution. There have been many cantilever structures built, but none with the constraints of our site, a project once though impossible which has unlocked the potential of a major national icon site. 

Many factors combined to make this project the one I am most proud of: the team I worked with, the success of our structural analysis - and the fact that members of the public will have no clue that the ten new levels of the new building are actually floating above the Money Box Building.

(Watch a video about 5 Martin Place).

(Below: the new atrium)

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