18 November 2016

Media release: Engineers says Wellington’s mid-height buildings worst affected

Engineers are finding unusual effects from the Kaikoura earthquake in that low rise buildings suffered minimal damage while medium rise buildings suffered significant damage.

New Zealand Society for Earthquake Engineering (NZSEE) President Peter Smith says there was an extraordinarily large release of energy much closer to Wellington than initially realised.

The shaking lasted 90 seconds, compared to 20 seconds for the February 2011 Christchurch event.

Mr Smith says how buildings respond in an earthquake depends on their height, stiffness and the nature of the ground they are on.

“At this stage in Wellington, it looks like buildings between eight and 15 storeys have been worst hit.  This quake has generated intense accelerations in buildings in this height range, especially those on softer soils.

“In contrast, short, stiff structures have experienced relatively low accelerations in this earthquake. This is the main reason why Wellington’s older buildings, which tend to be shorter, generally didn’t suffer any damage, even though some are categorised as earthquake prone. This effect is similar to that which occurred in the June 2013 Seddon earthquake. It’s important to realise that these buildings may still perform poorly in an event centred closer to Wellington.

Structural Engineering Society (SESOC) President Paul Campbell says engineers are continuing to assess buildings.

“Buildings might be undamaged or damaged in a way that doesn’t reduce their capacity to deal with future shaking. This means they may be just as safe as they were before the earthquake.

“Broken partition walls, ceiling and disrupted contents can look bad and be inconvenient but do not represent a significant threat to your safety.  Conversely, some buildings may have damage that is hidden from view but there will generally be clues to this that an experienced and knowledgeable engineer will detect.

“If an engineer assesses a building as suffering damage that is likely to reduce its capacity to deal with future shaking, this means more detailed assessment is needed. Carrying out a detailed assessment can take weeks, not hours”.

Institution of Professional Engineers New Zealand Chief Executive Susan Freeman-Greene says many of the lessons learned from the Canterbury earthquakes are now incorporated into the Building Code though have been included in few buildings to date.

“These include new guidelines for rapid assessment of buildings and training of engineers in how to do these assessments.

“Everyone is feeling uncertain about the weeks and maybe months ahead, given the potential aftershock sequence. Building owners seeking peace of mind may want to get an engineer familiar with the building’s construction type to give it a full assessment.

“If anyone has concerns about damage that their building has suffered and the affect this may have on future performance they are urged to seek engineering advice.”