July 9, 2015
After the Christchurch earthquake, everyone became much more conscious of whether the buildings they live and work in would stand up in an earthquake. This is a good question as early construction in New Zealand followed one of two paths; either we built like our Pommie ancestors using brick and stone, or we used the material that was cheap or even free (that was timber). The bush was being cut down near and far to clear land for farming, so timber was plentiful and cheap. At that time it was probably looked down upon as inferior to the more solid masonry buildings but in the long run, when you live in a shaky country like we do, the timber was much better than the masonry. Apparently, the first set of plans for Christchurch Cathedral had it all built in timber.
So as engineers, we are now being asked to say whether our buildings are safe. Nothing, of course, is quite that simple. What does safe mean? So to relate it to some numbers, what we do is describe it as a percentage of the strength that a new building would have. Even that is not that simple, as people are suggesting that even the present codes are not strong enough.
Well, since 2006 we have the IEP. The Initial Evaluation Process (IEP) assessment method is a quick method of identifying if a building is potentially earthquake prone. The IEP is a fairly crude look at the building based on its age, the type of materials used, the construction type and other factors. It can be a fairly quick and cheap procedure. The answer pops out the end as a percentage of New Building Standard. If it is below 33%, the building is called Earthquake Prone, if it is between 33% and 66% it’s called an Earthquake Risk . Above 66% is generally considered safe.
It’s quite crude, though, and if we do some numbers, we can arrive at the real strength of the building, which may be less or more than the IEP gives. But that’s the next part of the story. When you find your building is not as strong as you would like it to be. What can you do about it? Subscribe to the DBCon blog to make sure you don’t miss out on the next instalment on the IEP, and if you need an assessment conducted on your building contact the team at DBCon.