First published in the Listener, issue 3898, 22 January 2015.
One day, shortly before I started school, my father took me to his work at the Ministry of Works’ central laboratories, where he was head of structures. When his colleagues asked the inevitable, “How old are you?” I replied – just as Dad had coached me to – “Four point nine five.”
It got a laugh from his colleagues, who I’m sure appreciated the accuracy of my reply. An affinity for numbers and precision, along with rigorous attention to detail, is something we often undervalue, but in professions such as engineering they’re essential.
My father, Nigel Priestley, was a structural engineer who worked at universities in New Zealand, the US and Italy and whose consulting work took him to earthquake-prone countries around the world. According to Quincy Ma, president of the New Zealand Society for Earthquake Engineering, Priestley “revolutionised the design of structures to resist earthquakes” over the course of his career.
He died just before Christmas. His many awards and accolades, including an ONZM for services to structural engineering, have been noted in obituaries. But he was more than an engineer. He also read and wrote poetry, played classical guitar and was an accomplished carpenter. I think it was this mixture of precision and creativity that led to his best work, which was marked by a fresh way of looking at engineering problems and demonstrated in book-length accounts of how to apply these new ideas to the design of structures, particularly buildings and bridges.
Priestley’s “full metal jackets” – a cost-effective retrofitting system in which concrete bridge columns are wrapped in steel to reduce the risk of them collapsing in an earthquake – are now widely used in Californian bridges and highways and were adopted for the retrofit of the Thorndon overbridge in Wellington.
His most revolutionary move, though, was to reject the traditional force-based design that had dominated seismic engineering for its 60-year history and embrace and promote displacement-based design. This approach gives a better understanding of the forces and displacements within a structure and led to fundamental changes in the way new buildings are designed. Significantly, it allows engineers to actually dictate how a structure will respond in an earthquake. This philosophy was detailed in Displacement-Based Seismic Design of Structures,a 2007 book written by my father and colleagues Michele Calvi and Mervyn Kowalsky.
“The methodology set out in the book is rapidly replacing internationally the traditional force-based design methods,” says Richard Sharpe, Beca’s technical director of earthquake engineering.
Another significant advance in earthquake-resistant design is Presss (precast seismic structural system), developed by a team my father led. Whereas in the past buildings were designed to absorb force and crunch and grind at certain structural points, this new system designs buildings as a series of rocking blocks that can move independently of each other. To stop the blocks tumbling down in an earthquake, they are held together by steel tendons that allow the blocks to move but always pull them back to their original position. The beauty of this system, and the reason it’s being widely applied in the Christchurch rebuild, is that not only can you ensure lives are safe “but you also minimise the damage to the building or restrict damage to elements that can be easily replaced after the earthquake”, says Sharpe.
I returned to work this week in the Alan MacDiarmid Building at Victoria University, the first multi-storey building in New Zealand to use the tendon and rocking Presss system. I’m thankful for my father’s precision and attention to detail and to this country’s community of structural engineers who work to protect lives and property in these shaky isles and around the world.