2017 Statistics House Investigation Report
The expert panel's 2017 Investigation Report into Statistics House concluded that a combination of 4 factors contributed to the partial failure of lower floor segments.
What the panel found
Two of the factors — the flexible frames and style of floor construction — combined with significant shaking for up to 120 seconds, and localised amplification of the shaking, led to some precast concrete floor units losing support.
The combination of factors that led to the partial collapse of floor units in Statistics House was not anticipated by the design standards in place when it was built in 2005.
Design standards are regularly updated to incorporate new learnings. For example, Amendment 3 of the Concrete Structures Standard now contains more specific provisions that acknowledge the impact of beam elongation on flexible frame buildings and how seating of precast concrete floor units needs to be enhanced to accommodate this.
The Panel made 4 recommendations in its original report.
Investigation of existing buildings in the Wellington region with a similar design that may have been damaged by the Kaikōura earthquake
Existing buildings in the Wellington region (not just the Wellington City CBD) that have a similar design to Statistics House (buildings with precast floor systems and frames that may be affected by beam elongation) should be investigated as soon as possible to determine if precast floor seating problems exist as a result of the Kaikōura earthquake.
Building owners, tenants, consenting authorities and engineers should be provided with guidance to aid with the assessment of damage in existing buildings. This should build on the process begun by the Wellington City Council in December 2016 following the panel’s interim findings.
Notify the industry about issues with existing buildings with precast floor systems and frames that may be affected by beam elongation
MBIE, working with IPENZ and its technical societies, should immediately notify the engineering sector of issues relating to the use of precast floor systems in existing buildings that may be affected by beam elongation. This may occur in any region of New Zealand because a large earthquake is likely to create similar or greater demand on buildings.
Particular aspects that need attention include:
- the impact of beam elongation on precast floor systems, particularly in conjunction with multi-bay frames
- the need to maintain composite connection of the precast flooring to the in situ topping
- the need to review the precast floor support details
MBIE, working with IPENZ and its technical societies, should consider developing a longer-term plan for how to implement this recommendation. This could include disseminating guidance on how to assess existing buildings and providing guidance on standard methods of improvement, if required.
Access technical expertise to consider the implications for this type of design for new buildings
MBIE should access specialist expertise to:
- consider whether further controls should be placed on the design of new flexible buildings on sites which may be affected by significant ground motion amplification in regions of higher seismic hazard
- develop recommendations for amendments to Concrete Structures standard (NZS3101) to address the matters highlighted in recommendation 2 that would be applicable for the design of future buildings
- clarify the provisions of the Earthquake Actions Standard (NZS1170.5) for the application of P-delta effects in the design of new buildings
Review and undertake research into the provisions in the Earthquake Actions standard to ensure they reflect current knowledge of earthquake engineering practice
A review of the provisions in the Earthquake Actions standard (NZS1170.5) should be undertaken. MBIE should access specialist expertise to undertake the research to support this review. The research should focus on:
- the amplification of earthquake ground shaking due to basin-edge effects. Detailed geological and geophysical data should be incorporated into ground motion modelling. A focus on Wellington should be a priority for such research and the research should be extended to other urban centres as appropriate.
- the impact of duration of shaking, particularly for ductile building designs. The potential for large earthquakes to affect Wellington and other metropolitan centres may require duration to be more explicitly incorporated in the New Zealand Building Code system.
Our response to the panel's recommendations
- On the back of the targeted building damage assessment programme undertaken by the Wellington City Council, we wrote to other neighbouring councils to advise them that the 14 November 2016 earthquake may have affected buildings similar to Statistics House. This enabled these councils to contact building owners so they could undertake damage assessments similar to those performed in Wellington.
- The New Zealand Structural Engineering Society and its New Zealand Society for Earthquake Engineering issued guidance on how to assess damage to buildings which share the same design characteristics as Statistics House to ensure consistency amongst the assessments.
We worked closely with Engineering New Zealand and its technical societies to alert the engineering profession about the design issues with buildings similar to Statistics House.
We are working with Engineering New Zealand and the technical societies to develop comprehensive guidance to help with assessing buildings similar to Statistics House.
We have issued a warning on the use of loop bar details in precast concrete double-tee floors.
We have reconvened the committee for the Earthquake Actions Standard (NZS1170.5) and will be recommending further changes to be considered in this Standard based on what the investigation has taught us.
We have published Amendment 3 of the Concrete Structures Standard, which is now cited in our Building Code compliance documents.
We are commissioning further research to better understand basin-edge effects and the effects of earthquake duration.