June 2012

Muritai School Board of Trustees

Newsletter – June  2012

Board Report - Earthquake Readiness Survey

Tena koutou te whānau o te kura Muritai

We mentioned in our May newsletter that the Board had independently commissioned, and received, an initial survey which recommended a detailed assessment be undertaken of the two storey block.  We had hoped that due to the strengthening works undertaken by the Ministry of Education in 1998-2000, significant additional works would not be required.

Last week the Board received the second, more detailed, survey which reports on the building’s level of compliance with the current National Building Standard (NBS).  Unfortunately the building has been assessed as being significantly short of the current NBS and is categorised as “earthquake prone”. 

The Board’s property committee immediately met with experts from both the Ministry of Education and the engineers who prepared the report to discuss the findings, appropriate procedures and required remedial works.  We were encouraged by the Ministry’s proactive approach and we are both committed to moving as quickly as possible to bring the property up to as near as practicable to 100% of the NBS.

Importantly, we were also advised that there are other factors in addition to the NBS calculations, which go to make up actual risk and which also need to be considered in determining our next steps.  Central to these are the predicted consequences of a significant earthquake which should take into account that the calculations are based on a 1 in 1000-year earthquake and the building use (i.e. between 8:30am and 5pm, 5 days a week vs. (say) a residential building).

In ascertaining the impact of a significant earthquake, we have been advised that the most important factor is the structural characteristic of the building.  Once a building is categorised as earthquake prone (under 33% of NBS) this is then the key in determining whether it is suitable for continued use.  There have been commercial buildings and schools in the region which have been immediately evacuated following a structural survey and our experts, who have been involved in some of that decision making, have advised us that the main reason for this is that those buildings had “critical structural weaknesses” which would result in a total or partial collapse of the building in the event of a serious earthquake. Brick and masonry buildings are particularly vulnerable in this regard.

The expert advice we have received is very clear that our two-story building is of a very different construction and there are “no notable critical structural weaknesses that need to be addressed”.  Accordingly the Ministry’s recommendation, on the advice of the engineer is that it is suitable for continued occupancy pending remedial work. The report outlines this as follows:-

“The building in the east/west direction upstairs and in both directions downstairs has around 1/3 of the current standard strength, and therefore very close to a level that would not be considered earthquake prone.

The building is primarily a timber framed two-story building that has two concrete enclosures that support concrete stairs. Being a timber building it will have more ductility and it is likely that the actual capacity would be greater than those calculated. The main reason for this would be the ability of the timber frame to displace and hold together (unlike a brick building that would collapse suddenly once it meets its capacity), therefore dissipating the earthquake energy. Other factors that assist are the inherent strengths of the window frames, soft-board linings etc. that do not have published capacities but would add to the strength of the system. Capacities for these elements could be confirmed through detailed analysis or laboratory testing, both of which would not be deemed economically viable for this exercise.

As the building is timber framed we would expect that any collapse would be partial only and as the materials are of a lightweight, any collapse has a much reduced risk of serious injury than that of a collapse in a heavier concrete or brick building. There are no notable critical structural weaknesses that need to be addressed.  This building is constructed from lightweight materials and the risk of serious injury in this type of building is significantly reduced when compared to a heavier building with a similar calculated strength.”

Notwithstanding these mitigating factors, as the detailed structural survey put the main block at 12% of NBS the Board has decided that immediate remedial works should be undertaken.  This has been fast-tracked and work will be carried out next week, during the school holidays.  The proposed works, as designed by the engineers, will lift the building above 33% NBS and mean the building will no longer be classed as “earthquake prone”.

Once a building reaches this level, we are advised remedial works are usually scheduled over a 10-year period.  The Board has determined however to be more proactive and, in conjunction with the Ministry of Education, has this week instructed the engineers to prepare a remedial structural design plan for the strengthening of the remaining areas to lift the capacity of the building to, or as near as practicable to, 100% of the current standards.  The intention is to have this phase two work completed over the Christmas holidays this year. Given the design and consent process, the need for structural steelwork and the impact on classrooms the Board believes this is a realistic and achievable timeframe.  Having considered the alternatives and taken expert advice the Board is confident this is the best way forward and once completed we are told we will have one of the safest buildings in Wellington.

Obviously we are disappointed that the work is necessary at all, particularly given the strengthening work carried out 12 years ago, however we believe it is important to move quickly and comprehensively to ensure our families are in the safest possible environment.  We will of course report back to the community as soon as the remedial design plan is completed to update you on the next steps.

If you have any comments or queries or would like to discuss anything further please do not hesitate to contact any of the Board members.  Our contact details are as follows:-

Stuart Stock stu.stock@mac.com Chairperson

Andrew Bird bird@muritai.school.nz Principal
Melissa Coton coton@muritai.school.nz Staff rep
Olivia Paterson oliviapaterson@xtra.co.nz
Craig Griffiths caltgriffiths@xtra.co.nz
Julie Parker wattersparker@yahoo.com
David Griffiths wgtngriffs@xtra.co.nz
Carolyn Patchett cpatchett@yahoo.com

Whether you are off to find some sun, some snow or just some fun around Wellington this holidays we hope you have an enjoyable holiday break and we look forward to seeing you all in term 3.