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.