2018 Statistics House Investigation addendum report
The expert panel investigating earthquake damage to Statistics House had 3 extra recommendations after new information emerged during the building's demolition.
New information the panel considered
During the demolition of Statistics House, observations made by the engineering consultant who was monitoring the demolition, indicated that the seating provided for some of the precast concrete floor units was less than what was shown on the original design documents.
This new information led the Ministry of Business, Innovation and Employment (MBIE) to reconvene the expert panel who undertook the original investigation to determine whether the new information had any impact on the original investigation findings.
The panel concluded the new information did not change the original conclusions about the primary cause of the partial floor collapse.
The panel made 3 recommendations in the addendum.
Vulnerabilities of buildings with precast concrete components
MBIE should assemble specialist expertise to advise on an industry-wide approach to communicate and mitigate the performance risk of precast concrete floor systems, specifically for:
- building owners, who should be encouraged to retrofit precast floor systems in existing buildings for better protection of building occupants and their asset
- engineers involved in the assessment of existing buildings, who should be aware of the potential for progressive collapse when assessing floor supports
- engineers involved in post-earthquake building evaluation, who should be aware of the need to investigate floor supports for possible concealed damage.
Demolition considerations of buildings with precast concrete components
MBIE, in conjunction with industry bodies, should notify the building sector about implications of the form of failure of the double tee floor system observed during the demolition of Statistics House, specifically:
- designers, who all need to factor demolition performance into their whole-of-life safety in design obligations
- demolition contractors, who should be aware of the tendency for precast floors to collapse under impact loading and who need to ensure that the demolition methodology has adequately addressed the risk of adverse outcomes resulting from multiple floor level collapse.
MBIE and industry bodies should review the relevant provisions of the Concrete Structures Standard NZS3101 and the Concrete Construction Standard NZS3109 with a view to addressing better coordination between the design and documentation process and practical construction considerations.
This review should primarily look at the tolerance provisions for precast concrete construction with respect to seating requirements. Factors requiring consideration include the:
- sequence of casting (both precast flooring and in-situ support frames) and erection of precast components
- form of support used for the precast flooring units.
Our response to the panel's recommendations
- We propose to work with Engineering New Zealand and its technical societies to review existing assessment guidance and make sure the vulnerabilities of these building types are adequately communicated to the building sector.
- An industry-led research project is being established to develop guidance on how to retrofit these types of floor systems.
- We will review existing guidance for rapid post-disaster building assessment and may consider advising MBIE-trained building assessors about extra precautions that may be necessary when performing post-earthquake building evaluations on these types of buildings.
- An industry-led initiative is underway to develop New Zealand-specific guidance on how safety-in-design needs to be considered for the full extent of a building's life.
- We will remind BCAs about the importance of checking that professional advice has been obtained when a building is demolished. A comprehensive demolition methodology will typically need to be developed for the safe demolition of a multi-storey building.
- We will review the relevant provisions for construction tolerances in the current Building Code compliance documents and consider whether it is appropriate to review Standards cited in the Building Code compliance documents or alter other parts of the Building Code system.