MBIE announces revision of engineering assessment guidelines

On 1 July 2017, the Building (Earthquake-prone Buildings) Amendment Act came into force. The EPB methodology is the part of the system that specifies how potentially earthquake-prone buildings are to be identified and assessed. It requires engineers carrying out assessments to use the Engineering Assessment Guidelines, which have now been technically revised section C5 of the Guidelines based on learnings from the Statistics House investigation following the Kaikōura earthquake. It also updates other technical provisions related to existing concrete buildings. It represents engineers’ latest thinking on precast concrete flooring.

Essentially, the revised section C5 has expanded and enhanced material on precast concrete floor systems. There is new information on the material properties of older concrete and reinforcing steel, and on assessing older bar splices and newer bar couplers. An improved column shear strength model has been added, along with how to address more modern beam-column joints. By changing the Engineering Assessment Guidelines, MBIE are taking a sensible approach, assessing how many buildings it will effect and what the impact could be, rather than just changing the Building Code and tarring all buildings with hollow-core floors as “earthquake prone”, which could have had severe consequences.

Property Council has been working with MBIE to ensure a more measured approach than initially proposed, and we are pleased to see that the Ministry has listened and signalled that engineers will work with building owners and managers to find a solution whilst still ensuring the safety of New Zealand’s building stock.

What are the changes?
  • There is no change to the earthquake-prone building management system introduced on 1 July 2017. This means there are also no changes to the EPB methodology or the Engineering Assessment Guidelines.
  • C5 is a section of the Engineering Assessment Guidelines. It tells engineers how to carry out detailed seismic assessments of concrete buildings.
  • A revised version of Section C5 ‘Concrete Buildings’ was released in November 2018 as a technical proposal to revise the Engineering Assessment Guidelines. This will sit alongside the original C5 version within the Engineering Assessment Guidelines that was released in July 2017.
  • The revised (yellow) section C5 reflects what engineers learned from the Statistics House investigation following the Kaikōura earthquake. It also updates other technical provisions related to existing concrete buildings. It represents engineers’ latest thinking on precast concrete flooring.
  • The revised (yellow) section C5 tells engineers how to best assess buildings with precast concrete flooring, given what we now know about how these floors behaved in earthquakes.
  • The revised (yellow) section C5 includes information to assess more types of precast concrete floor systems.
  • Engineers can use the revised (yellow) section C5 when carrying out seismic assessments, except when they are assessing a potentially earthquake-prone building under legislation. In that case, section C5 in the Engineering Assessment Guidelines must be used.
  • Over the next few years, MBIE is collaborating with Engineering New Zealand to gather feedback on the revised (yellow) section C5.
  • MBIE needs evidence of how the technical changes to section C5 would change assessments of potentially earthquake-prone buildings before considering incorporating it (as legislation) into the Engineering Assessment Guidelines. The Building Act 2004 requires consultation and a parliamentary process before the EPB methodology (including the guidelines) is changed.
Who developed the revised (yellow) section C5?

The guidelines were developed by technical experts from New Zealand engineering technical societies in a partnership with MBIE.

What should a building owner do if they own (or a tenant in) a building with a precast floor?

It is recommended that the building is assessed against the revised (yellow) section C5.

Should buildings with precast floors assessed under the original version now be reassessed?

It is recommended that buildings that may not have had the floor system specifically evaluated in a previous assessment be re-assessed against the revised (yellow) section C5. If building owners aren’t sure about the scope of any previous assessment, they should check with the engineer that carried it out.

What can an owner do if they have an EPB that has precast concrete floors?

If a building has been identified as potentially earthquake prone, an engineer can only use section C5 in the Engineering Assessment Guidelines for a seismic assessment. For buildings with the types of concrete elements not fully addressed by the original section C5 (such as precast floors), engineers can assess using the concrete structures standard, NZS3101. This is fully enabled through the Engineering Assessment Guidelines.

What should a building owner do if their building receives a lower rating using the revised (yellow) section C5?

They should notify their tenant and talk to their engineer about options for strengthening work. If the rating has not fallen below 34%NBS, and the Territorial Authority does not identify it as a potential EPB, any strengthening work is at the discretion of the owner. Building owners may see benefits in strengthening to levels well above the threshold of 34%NBS, to ensure life safety and to avoid any potential future strengthening costs.

Will the revised (yellow) section C5 produce different results from the section C5 in the Engineering Assessment Guidelines?

Potentially. It depends on the individual building.

The revised (yellow) section C5 takes into account an updated understanding of how precast floors can perform in an earthquake, so it’s possible a building could be rated lower. However, the ratings for some buildings may increase.

MBIE and Engineering New Zealand will be gathering feedback on the changes over the next few years.

 

> Read more about this issue
> Download the Technical Proposal to Revise Section C5

 

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