Thursday, September 23, 2010

Bryan Leyland: Earthquakes, snowfalls and road tunnels

Recent events in the South Island highlight what engineers can–and cannot–do.

My favorite definition of an engineer is "someone who can do for five bob was any fool can do for a quid”. Engineers strive to do the best job they can in the light of the knowledge available at the time without wasting huge amounts of money. As a result we have progressed from early steam engines with, perhaps, 5% efficiency to modern power stations at 60% efficiency. Bridges have got longer, stronger lighter and cheaper and so on. But advances in technology has always been punctuated by periodic failures. Detailed analyses of these failures has been a major factor in designing machines and structures that are stronger and safer. The process is continuous and, every now and then, there will be failures. Nevertheless, in the long run everyone will benefit from the lessons that have been learned. In engineering, as in most–or all–aspects of modern life, risk can be minimized but it cannot be eliminated.

The failure of the stadium in Southland is an excellent example of this. Preliminary evidence indicates that the roof failed at a snow loading that was above the design loading. A few years later, the code was updated and the design snow loadings were increased. Detailed examination of the evidence and analyses of the failure will, for sure bring out valuable lessons that will be incorporated in future codes. But there is one thing we can be sure of: “climate change” (of the man-made variety) had nothing to do with it. There is abundant evidence around the world and, in particular from New Zealand, that past warm periods have coincided with less extreme weather. But if, as many people expect, the recent unusually long sunspot cycle is a precursor of significant cooling, we can expect more extreme weather.

The Christchurch earthquake demonstrates that natural hazards are real and dangerous and also also provides many valuable lessons for the future. But what many people do not realize is that when buildings are designed to withstand an earthquake, the primary requirement is that they should not collapse and kill everyone inside. Buildings are designed to be resilient and sway in an earthquake. As a result of the swaying there will be some damage. In Christchurch, even though it was a severe earthquake, very few of the multistory buildings suffered any significant damage. Even those built to earlier and less strict earthquake codes survived very well indeed. Those that were damaged had fault movement directly underneath them or ground liquefaction resulting from the shaking causing the ground to settle and the ground water to come to the surface. Basically, the soil turned to quicksand. When that happens, the strength of the building is not all that relevant.

Everyone in New Zealand should be glad that we have had strict engineering codes for many years and that they are regularly updated. In many other countries an earthquake of this magnitude could easily have flattened all towns and killed thousands of people. Which is exactly what happened in Haiti. The 1989 earthquake in San Francisco Bay area was of similar magnitude yet killed 63 people, injured 3800 and left 12,000 homeless. And this in spite of the fact that California has earthquake codes.

On the other hand, the decision on the Waterview tunnel is an example of what happens when cost and public safety are ranked second to the views small number of people. (For readers out of Auckland, the Waterview tunnel will connect the new motorway from Manakau and the airport to the Northwestern motorway. It is a connection that, if it that had been done 10 years ago, could have been carried out for a few hundred million dollars. The owners of a few hundred houses that could need to be removed for a junction on the surface objected strongly and persuaded the politicians that the tunnel was the politically acceptable option. It didn't seem to matter to them that it added about $1 billion to the cost.) The sad story starts off with, of all things, the Public Works Act. This act decrees that when property is taken for a public work, the compensation that can be paid is limited to the fair value of the property. It simply does not permit additional payments for the inconvenience of being moved, for the disruption to lives and so on. So the residents whose houses were under threat had two options–protest loudly or accept what they, with good reason, held is to be totally inadequate compensation. They "won" and the New Zealand public probably paid $1 billion extra for the tunnel. The chances are that $100 million or so paid as compensation would have resulted in a win-win solution for everyone.

Not only will the tunnel be more expensive, but operating and maintenance costs will be very high. It will have to be continually staffed, large amounts of electricity are need to drive its ventilating fans and every few weeks the tunnel will to be closed down for maintenance work. I understand that the aggregate cost of operation and maintenance will, in the long term, exceed the cost of building the tunnel.

Without the tunnel, there would be something like $1 billion available that could have done an enormous amount of good helping the disaster stricken people in Christchurch. But instead, we chose "to spend a quid doing what any engineer could do for five bob". And, saddest of all, we are most unlikely to learn anything at all from this tragic waste of public money.

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