Preparing for earthquakes

Wellington, the capital of New Zealand, has experienced some of the country’s largest recorded earthquakes. Wellington City Council is taking steps to prepare the city for another large quake.

Recently acquired seismic data suggests that Wellington is at risk from a much larger earthquake than originally thought when many of its buildings were constructed and therefore new building standards have been announced. This has resulted in building owners in Wellington, including Wellington City Council itself, being given notice that their buildings, which had previously passed the old standards, are now below par according to this new seismic data – and they have 10 years or so to seismically strengthen their buildings or they will no longer be habitable.

One building on the ‘not to standard’ list is the Wellington Town Hall. Built in 1904 and home to the Mayor’s office, this masonry building is constructed of brick and did not have the benefit of reinforcement when first built. As a building of heritage value, pulling it down is not an option – it must be seismically strengthened. Assessing the options has been the job allocated to GHD's Wellington structural team.

While seismic strengthening techniques for new buildings are well established, techniques for retrofitting existing buildings are very much building-dependant. For example, the challenge is to strengthen the Town Hall structure while preserving the historical and architectural fabric of the building. The GHD team needs to find the most relevant and appropriate remedy.

Regardless of how the Town Hall is strengthened, one thing is clear – it will be an expensive process. Options include base isolation (putting the building on rollers) or the use of fibre-reinforcement technology. The costs are unknown and are extremely difficult to estimate. The cost to retrofit the Wellington Town Hall could be in the region of NZ$20 million.

There are hundreds, if not thousands, of buildings facing the same future; some publicly owned, others privately. For now, owners must grapple with the news first, and then a decision as to what to do with the buildings they own.

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