The latest batch of quakes to hammer central New Zealand got me thinking. In past decades the usual face of such events were street-scapes of broken buildings and scattered debris, typified by the ruin that struck Napier and Hastings in 1931.
That disaster cued more than half a century of active quake-proofing measures, bolstered by several revisions to the original 1935 code. And so today buildings in cities such as Christchuch and Wellington – both hit by multiple heavy quakes since 2010 – stay standing.
But that, it seems, is all many of them do. The Christchurch experience was salutary. Two modern buildings collapsed in Christchurch in the February 2011 quake, provoking much of the appalling death toll. Others still stood. Except that, on inspection, they had to come down anyway because of fundamental structural failure. Sometimes it was foundation problems: in 2013, when I visited the quake-riven city, I saw a row of high-rises looking for all the world like crooked teeth. All were due for demolition.
It’s been the same in Wellington. The two heavy quakes of 2013 and the Mw 7.8 Kaikoura shake last month – which delivered much of its punch north to the capital – didn’t collapse any buildings. But a number of them have been damaged beyond repair and are going to come down anyway – taken down, urgently, by demolition crews before they collapse in aftershocks. They include new parking buildings and a very modern building on the waterfront that – in theory – was put up to the latest standards. Ouch.
We can build structures that don’t collapse or shed their outer walls in quakes, it seems, but we can’t build structures that are truly earthquake resistant – able to shrug off the effects and carry on. The plus side is that this still works as a way of saving lives. People can get out, and buildings don’t shed their walls into the street and crush passers-by. But the focus on quake-proofing has always been structures that simply shrug off the damage, and I have to wonder what’s gone wrong. Especially when you realise that most of what’s being demolished are the most recent buildings, put up in the last decade or so. Whereas older structures such as the Wellington Railway Station still stand.
There will be an investigation – government’s announced it – but I can’t help thinking that a couple of factors have been at work here. One of them is that older seismic-resisting structures such as the station – which was designed before the 1935 code – were radically over-engineered. That particular building was erected on reclaimed land and special attention was paid to seismic proofing, including obtaining Japanese expertise. The other issue is a change of code in 1992 to kind of ‘market-driven’ model. Until then seismic code had been quite prescriptive, even down to the kinds of material to be used. Now it became more general – a requirement to meet certain loading standards. But exactly how those standards were met was up to the individual architect and engineers.
The philosophy was in line with the general mood of de-regulation that was suffusing New Zealand at the time. But it introduced a lot of variables, including one of the pitfalls of engineering – assumptions. If the assumptions around which a quake-loading was being calculated were wrong, then the building wouldn’t perform as expected in the crisis. And to me, that looks disturbingly like what has been going on.
No doubt the answers will come out when it’s all investigated. Meanwhile it looks like Wellington is going to see a lot of demolitions in the near future.
Copyright © Matthew Wright 2016