Kaikoura Earthquake Highlights Deficiencies in Building Code

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Investigation into the Performance of Statistics House in the 14 November 2016 Kaikoura Earthquake - Ministry of Business, Innovation and Employment

What caused the collapse?

Statistics House is a six story reinforced concrete office building in Wellington.  It was built in 2005 in line with the industry standard practices of the time.  During the Kaikoura earthquake two floors in the building partially collapsed.    

Building and Construction Minister Nick Smith has commented “the performance of Statistics House in the Kaikoura Earthquake was unacceptable.” Despite the earthquake being unusually long (120 seconds) “a modern building like Statistics House should not have had life-threatening structural damage.”  An investigation was commissioned to consider what caused the buildings poor performance during the earthquake taking into account the design and construction of the building and land influences.  The overall aim of the report was to understand the implications for the building regulatory system including the performance of the current building code and guidance published under the Building Act 2004.

The report has found the collapse was due the following combination of factors.

  1. the high level of flexibility in the building’s design,

  2. the style of floor construction (pre-cast floor slabs),

  3. the duration of the earthquake and

  4. Basin-edge effects. 

The design of Statistics house was flawed.  The frame of the building was designed to flex and ‘stretch’ with an earthquake.  However the extent of this movement compromised the support of more rigid floor slabs which broke and collapsed.

Wellington sits on the edge of a geologic basin where softer soils have been deposited.  Basin edge effects cause amplification of ground shaking at the edge of the basin resulting in concentrated areas of damage.  This phenomenon has been likened to “the way sea waves respond to a wall in an enclosed bay.”  There is a lack of international research available on this issue so one cannot conclusively predict where basin-edge effects exist in order to alter the design of buildings to withstand these effects.

This interrelationship of factors was not considered in the standards Statistics House was built to.  The findings of this report have signalled the need to make changes to the current requirements and building code, which are regularly updated to incorporate new learnings. 

Recommendations

The report concludes with the following recommendations:

  1. Buildings of similar construction to Statistics House (buildings with precast floor systems) in the wider Wellington region should be investigated for possible damage.  The New Zealand Structural Engineering Society and the New Zealand Society for Earthquake Engineering have issued guidance on how to assess damage in these types of buildings to ensure consistency

  2. The Ministry of Business, Innovation and Employment (MBIE) together with the Institution of Professional Engineers New Zealandshould work together to notify the engineering industry of design issues with existing buildings similar to Statistics House and supply comprehensive guidance to assist engineers in assessing these types of buildings

  3. Specialist expertise should (and has been) engaged to consider what amendments need to be made to the Concrete Structures Standard and Earthquake Action Standard (which put simply looks at how structures are affected by ground movement) to ensure newly designed buildings can cope with beam elongation during long duration earthquakes. 

  4. Research should be undertaken to further understand the impact of basin edge effects during an earthquake.  This research will involve international collaboration with countries such as Japan and the United States of America which both have cities (Kobe and Los Angeles) affected by basin edge effects.  Additional research will also consider the effect of earthquakes with a longer duration on buildings in Wellington and other metropolitan centres to consider whether ‘duration issues’ may need to be more expressly incorporated in the New Zealand Building Code. 

Additional building law issue

Nick Smith has also identifiedthat “the MBIE has limited powers to follow up on design deficiencies like those identified in this report beyond those specifically provided for following civil emergencies.  This means MBIE cannot require building owners to follow up on these sorts of potentially serious technical problems.  I have asked MBIE to report on whether additional powers are needed in the Building Act.”  If these additional powers are given to MBIE remains to be seen.

Comment:

Cecily Brick from Fee Langstone says the unexpected failure of modern buildings appropriately built to code will be a concern for underwriters.  It reinforces the unpredictable nature of earthquakes and the amount that is still unknown despite all the advances in earthquake engineering in modern times.