The original draft detailed seismic assessment (DSA) of the Heretaunga Block (issued on 8 March 2022) rated five structural or non-structural elements at 15% of the New Building Standard (NBS) at IL3.
We asked an independent engineer to go through a peer review process of the DSA with the existing engineers. They agreed that the precast concrete façade panels are the only part of the building rated at 15% NBS at IL3 in the final draft DSA. Most other structural parts of the building have been rated at 34% or higher.
The result does not change the overall status of the building. With one element still at 15% NBS at IL3, the building is still considered earthquake-prone (which is determined by Hutt City Council). The other elements are considered earthquake risk. We are therefore recommending the Board confirms our earlier decision to relocate services out of the building as soon as reasonably practicable.
Ratings and what they mean
Seismic ratings asses the level of risk for a building compared to an equivalent new build. The NBS (New Building Standard) does not predict expected performance in a particular earthquake, as every earthquake is different in terms of location and depth of the epicentre, and frequency of shaking. For example, of the more than 700 designated earthquake-prone buildings in Wellington at the time of the Kaikoura earthquake, only a small number recorded any damage, and it is understood that none experienced structural failure.
A building with a rating less than 34%NBS is not considered a dangerous or at pending risk of failure in an earthquake. However they do signal action should be taken to address the seismic weaknesses identified.
Previous assessments
The last seismic assessment of Heretaunga Block was carried out in 2011, and the building met the required standards of performance.
In 2017, the technical guidelines for these assessments were updated to reflect learnings from the Christchurch and Kaikoura earthquakes. Buildings such as hospitals are also held to a higher standard than other buildings because of their role in emergency support after a major disaster. As a result, the assessments of different parts of buildings (such as columns and beams, flooring, facades and stairs) became stricter.
The 2017 changes did not require owners to undertake new assessments – they provided updated guidance on how buildings would be assessed in the future. Engineers have confirmed that seismic ratings are essentially comparing how a building will react in an earthquake, compared to an equivalent new building. These ratings do not represent a specific assessment of safety.
In 2018, Hutt Valley DHB and Capital & Coast DHB began reviewing our hospital network and facilities to support the delivery of high quality and safe patient-centred care for our growing communities.
In 2019, Hutt City Council identified the Heretaunga building as potentially earthquake-prone – due to its age and height – and gave us a year to provide an engineering assessment. We supplied the 2011 DSA, which the Council confirmed complied with the requirements of the Earthquake Prone Building methodology.
In 2021/22 we asked for an updated seismic assessment of the building, as part of a wider review of our hospital network.
After receiving the first draft engineering on 8 March 2022, we set up a project team and began working with engineers to understand the situation, gather more information, and investigate options for the next steps. This included working with clinical and healthcare experts to ensure we continued prioritising staff and patient safety.
The Board was advised of the engineering assessment and planning on 13 May 2022. They then received updates on Thursday 7 June and 22 June 2022.
You can read the engineering reports and Board papers below:
