Timber-framed school buildings' earthquake resilience
As timber-framed buildings are generally of low risk to life safety, they are not included as priority buildings for assessment or strengthening in the Ministry’s earthquake resilience (EQR) programme. As a board of trustees, you can, however, continue to plan projects for your timber-framed buildings and take measures to improve their overall performance.
- Research into the performance of timber-framed buildings
- Assessing timber-framed school buildings
- Strengthening timber-framed school buildings
A large proportion of school buildings in New Zealand are timber-framed. Traditional engineering assessments often score these buildings as below the required New Building Standard (NBS) because they have few identifiable bracing elements. However, these buildings performed very well during the Canterbury earthquakes with no incidents of serious injury or death.
Since the earthquakes, we have extensively evaluated the performance of timber-framed buildings. The work has included:
- detailed seismic analysis of a range of our standard classroom blocks
- ‘destructive testing’ of standard one- and 2-storey classroom blocks in Wairarapa and Christchurch.
Destructive testing of single-storey classroom blocks
We commissioned the Building Research Association of New Zealand (BRANZ) to conduct destructive testing of standard types of timber-framed classroom blocks. These tests confirmed that the strength of the timber-framed buildings is:
- significantly greater than previously calculated
- in many cases, over 100% of the NBS.
Note: Timber-framed buildings constructed under modern seismic code requirements are expected to have earthquake resilience that meets or exceeds current Building Code requirements.
In November 2013, Housing New Zealand commissioned BRANZ to undertake a similar full scale test of a 2-storey timber-framed housing unit in Upper Hutt. The results have also indicated significant resilience in these buildings, at a level of over 5 times the calculated strength.
Further work is being carried out as part of the wider national project to update the New Zealand Society for Earthquake Engineering (NZSEE) seismic assessment guidelines.
Research about structural resilience of school gymnasiums and halls
Recent research shows that school gymnasiums are structurally more resilient than previously thought. This may significantly reduce costs of future school strengthening works.
In mid- 2015, the Ministry of Education and the Ministry of Business, Innovation and Employment (MBIE) jointly commissioned BRANZ to conduct full scale testing on a replicated gym wall using several scenarios. The purpose of this research was to support more accurate and realistic structural assessments of assembly type of school buildings, such as gymnasiums, halls, and libraries. The testing results show that the gym is much stronger than calculations previously suggested.
The results of these tests have wider implications for similar type of structures across the country. The information is being fed into the update of the New Zealand Society for Earthquake Engineering national guidelines for seismic assessments.
The Ministry’s Engineering Strategy Group (ESG) are currently working with BRANZ and MBIE on how to apply the testing results and new assessment methodology to future seismic assessments of school gymnasiums and halls.
Further updates on these development will be available early 2016.
To download reports on destructive testing, go to:
- Ministry report – Structural testing of a standard classroom block – Carterton [PDF, 1.1 MB]
- BRANZ report – Load testing of 2 classroom Avalon block at South End School [PDF, 3.4 MB]
- Ministry report – Structural testing of a standard classroom block – Christchurch [PDF, 1.6 MB]
- BRANZ report – Load testing of a Dominion block at Hammersley Park School [PDF, 5 MB]
- A further paper detailing the work undertaken by the Engineering Strategy Group (ESG) to establish the resilience of timber-framed school buildings in the period 2012 to 2014 is available here:
- To watch the testing at Hammersley Park School, go to Hammersley Park School Destructive Testing (YouTube website) (external link) (1 min, 54 sec).
- BRANZ report - Gymnasium wall testing [PDF, 2.3 MB]
In 2013, our ESG developed our guidelines for the seismic evaluation of timber-framed school buildings. This guidance is for professional structural engineers assessing timber-framed school buildings for seismic strength. They only need to use these on school projects when seismic assessments are considered necessary, such as on buildings:
- in Christchurch
- on councils’ earthquake-prone building lists.
We do not encourage seismic assessments of timber-framed school buildings because of their generally low risk to life safety.
To read the guidelines, go to Ministry of Education Guidelines for the Seismic Evaluation of Timber-Framed School Buildings [PDF, 689 KB].
Future assessments of timber-framed buildings
Investigation findings indicate timber-framed buildings are not earthquake prone under current legislation. A different approach is taken to the assessment and strengthening of timber-framed school buildings to the approach used for all other school buildings.
The ESG provided its findings to the NZSEE in its work report on the seismic performance of timber-framed school buildings. NZSEE used this information to update its Assessment and Improvement of the Structural Performance of Buildings in Earthquakes 2006.
To read ESG’s work report, go to Engineering Strategy Group: Understanding the Seismic Performance of Timber-framed School Buildings [PDF, 1.2 MB].
We expect changes will be made to the way timber-framed buildings are assessed for earthquake resilience. We are working on this issue with:
- the Ministry of Business, Innovation and Employment, which is developing new methodology for the seismic capacity assessment of buildings
- Local Government New Zealand and local authorities.
Although timber-framed buildings are considered low risk from a life safety perspective, and are not a priority to assess and strengthen, there are some things you can do to increase their earthquake resilience when doing modernisation projects.
This includes measures such as relining with seismically rated plasterboard and installing the associated floor and ceiling connections. This work will increase the performance of the building in earthquakes and result in less damage. Often these enhancements add little cost to projects.
When preparing your 10 Year Property Plan (10YPP), consider if any of your timber-framed buildings:
- have had any internal walls removed so that walls are now more than 10 metres apart
- sit on a sloped site
- have a brick veneer that was built before 1996 and is higher than 1.5 metres off the ground.
Tell your property advisor about any building with these characteristics. They can be dealt with as buildings are upgraded and modernised.
Timber-framed buildings that are below 67% of the NBS
If a timber-framed building is assessed at below 67% of the NBS, the modernisation measures should bring it up to standard. Timber-framed buildings don’t usually need additional bracing elements to achieve 67% of the NBS.
Even if a building is above 67% of the NBS, you should still include these measures in modernisation projects. In that way, the building will become more resilient at minimal extra cost.
For more information about NBS, go to earthquake-prone school buildings identification.
Replacing heavy tile roofs
Replace heavy tile roofs on timber-framed buildings with a lighter material to reduce the risk in an earthquake. See strengthening school buildings for earthquake resilience.
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