Ministry of Education Canterbury Earthquakes Impact on the Ministry of Education’s School Buildings Ministry of Education Canterbury Earthquakes Impact on the Ministry of Education’s School Buildings Prepared By Opus International Consultants Ltd Toby Tscherry Christchurch Office Structural Engineer 20 Moorhouse Avenue PO Box 1482, Christchurch Mail Centre, Christchurch 8140 New Zealand Reviewed By Telephone: +64 3 363 5400 Will Parker Facsimile: +64 3 365 7858 Technical Principal – Earthquake Engineering & Building Structures Date: 16 January 2015 Reference: 5-C2102.00 Status: Issue 10 FINAL © Opus International Consultants Ltd 2015 Canterbury Earthquakes – Impact on the Ministry of Education’s School Buildings i Executive Summary This report has been written for the Ministry of Education (“the Ministry” or MoE). The purpose of this report is to review performance of school buildings in the Canterbury earthquake sequence. The intent is to assist the Ministry of Education in improving the resilience of their current and future school buildings in Christchurch and throughout New Zealand. The post-earthquake review sampled 70 school buildings in Canterbury classified into 25 types. The majority of school buildings reviewed are single storey, with the remainder being a maximum of 2 storeys. Buildings selected range in age from the 1930s through to 1990s. The buildings have been chosen to be representative of school blocks throughout New Zealand, thus the majority of the sample captures buildings from the 1950s through to the 1970s, when ‘standard’ designs were used nationally (or regionally). After this period, one-off designs prepared by local architects seem to dominate the building stock. It was not attempted to capture these newer designs in the sample, because the lessons from these one-off designs have less relevance to the national portfolio. Conclusions drawn about safety emphasize that there were no fatalities on school sites although some injuries occurred, mostly resulting during egress. The Ministry’s earthquake strengthening programme has been effective; it prevented building collapse, provided a safe environment for teachers and students and limited damage to buildings that would otherwise have been more severely affected. A significant conclusion is that a large proportion of damage was the result of ground deformation. A key recommendation is that the Ministry consider this and other site related risks nationally. Conclusions on structural performance are: Lightweight wall and roof timber buildings have performed very well generally and in excess of their calculated capacity. Seismic retrofit work undertaken has been effective. A large proportion of building damage was due to ground deformation. Lightweight buildings with suspended timber floors on shallow footings generally accommodate ground deformation well and can often be quickly and cost effectively re-levelled. Overhead heavy building services or items unsecured on shelves can be a falling hazard. Most heavy roofs have been removed and replaced with lightweight material, which has reduced the seismic load and damage. Where blocks have been joined together and the alignment of the principle axes are no longer maintained such that the footprint is not symmetrical, i.e. joined together to form a T shaped footprint, increased damage was observed. Heavy veneer cladding increases damage to internal linings. Overhead heavy veneer can be a falling hazard if not well tied to timber framing, particularly above doors and windows. The open plan blocks have minimal bracing which increases frame distortion and damage. Some CEBUS type buildings have external nail plates that have failed during shaking without resulting in collapse. These can be simply retrofitted. One of the Pre-1930’s Two Storey Block’s has Potential Critical Structural Weaknesses while up to 11 others have structural weaknesses. 5-C2102.00 | January 2015 Opus International Consultants Ltd Canterbury Earthquakes – Impact on the Ministry of Education’s School Buildings ii Site Considerations – Recommendations Buildings and Infrastructure An egress and evacuation plan should be put in place for each school site. The main issues are concerning stuck doors due to differential settlement and potential fall hazards. The assembly point should also be considered. Overhead falling hazards relating to poorly tied brick veneer, heavy building services or items on shelving should be assessed, and if required secured or removed to a lower height. Consideration should be given to assessing and, if required, strengthening, or removing the veneer at height to mitigate this risk in a future significant earthquake event. Lowering the veneer will have the added benefit of reducing the seismic load on the buildings’ structure and improving its overall performance. Consideration should be given to upgrading site infrastructure during significant developments. This would reduce the extent of aged, frequently extended, brittle pipe networks present on many school sites. Consideration should be given to the assessment of schools’ existing infrastructure networks, for their condition and capacity i.e. compliance and vulnerability. This would indicate a need for the upgrade of any existing infrastructure with newer, more robust systems. This also reduces the risk of major costs associated with repairing older systems, when repairs carried out in the future might trigger the requirement for a Building Consent. Discussion with Councils should also be considered to seek clarity on compliance requirements. Consideration should be given to contingency measures for lifeline services (water supply & sewer). Consider options for hardstands that include ‘full design life’ to mitigate known geotechnical risks. Process – Recommendations and further review Issue minimum standard brief and guidelines for engineering assessment and design which embodies current ‘best practice’. (We note that the Ministry have subsequently issued guidelines on importance level for retrofit and new design). Consider adopting damage resistant designs in high seismicity areas. This could also reduce the cost to repair non-structural damage, which is estimated to be approximately 70% of the total repair cost for commercial buildings. Review processes around construction quality control and construction monitoring by the designer and Territorial Authorities’ (TA’s) to ensure efficiency and confidence that the design intent is achieved during construction. Consider setting up a review panel, perhaps a continuation of the Engineering Strategy Group (ESG) or similar to USA practice where an independent consultant from an approved panel reviews design and or construction. Learnings from other commercial and Ministry of Education buildings should be applied to the portfolio, for example: Stairs; review in accordance with Ministry of Business, Innovation and Employment (MBIE) guidelines. Precast panels; especially connections and requirements for ductility. Shear walls; in line with interim design guidelines by Structural Engineering Society New Zealand (SESOC). Cross bracing; particularly Reid Brace especially connections and requirements for ductility. 5-C2102.00 | January 2015 Opus International Consultants Ltd Canterbury Earthquakes – Impact on the Ministry of Education’s School Buildings iii Contents Executive Summary .................................................................................................... i 1 Introduction ....................................................................................................... 1 2 Assessment Scope .............................................................................................. 1 2.1 Limitations ........................................................................................................................ 1 2.2 Infrastructure .................................................................................................................... 2 2.3 Peak Ground Acceleration ................................................................................................ 2 2.4 Geotechnical ...................................................................................................................... 7 2.5 Potential Structural Weaknesses .................................................................................... 12 3 Selection of Buildings ........................................................................................ 12 3.1 Considerations for Selection ........................................................................................... 12 3.2 Selection Criteria ............................................................................................................. 12 3.3 Buildings Selected ........................................................................................................... 12 4 Building Type Structural Review .......................................................................16 4.1 Rating System ................................................................................................................. 16 4.2 Flowcharts and Reference Material ................................................................................ 16 5 Key Findings .................................................................................................... 20 5.1 Summary of Building Results ......................................................................................... 20 5.2 Discussion/Analysis