REPORT STAGE 2 REPORT. Earthquake Commission. Darfield Earthquake 4 September 2010 Geotechnical Land Damage Assessment & Reinstatement Report

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1 REPORT Earthquake Commission Geotechnical Land Damage Assessment & Reinstatement Report STAGE 2 REPORT

2 Prepared by Tonkin & Taylor Limited for the Earthquake Commission Stage 2 Report November 2010 Applicability This report was produced for the Earthquake Commission (EQC) to assist in assessing insurance claims made under the Earthquake Commission Act The report is not for any other purpose. It is recognised, however, that the report may assist central and local government planning for effective long-term solutions for the affected communities. Neither Tonkin & Taylor Limited (T&T) nor the Earthquake Commission accepts any liability to any third party with respect to this report.

3 REPORT Earthquake Commission Geotechnical Land Damage Assessment & Reinstatement Report STAGE 2 REPORT Report prepared for: EARTHQUAKE COMMISSION Report prepared by: Tonkin & Taylor Ltd Distribution: EARTHQUAKE COMMISSION Tonkin & Taylor Ltd (FILE) November 2010 T&T Ref: Stage 2 Report

4 Table of contents Applicability 1 Introduction 1 2 Recovery process Zone A Process Programme outline Zone B Process Programme outline Zone C Process Programme outline Areas not covered by mapping Process Programme outline 4 3 Land performance categories Summary of categories Target land performance standard 6 4 Design options Remediation options Opportunities in the detailed design Locate engineered land remediation works within public land Setting a higher target land performance standard 12 5 Reconstruction programme 13 6 Glossary 15 ii Appendix A: Waimakariri District Appendix B: Christchurch City Appendix C: Selwyn District

5 1 1 Introduction Tonkin & Taylor Ltd (T&T), on behalf of the Earthquake Commission (EQC), has assessed most of the land damage to the main urban areas in the Canterbury region resulting from the Darfield Earthquake sequence which started on 4 September This Stage 2 report follows on from a previous report (Stage 1), published in October 2010 and provides aggregated maps of land damage for the majority of residential properties affected by land damage arising from the Darfield Earthquake sequence. The report presents practical remediation methods on a suburb-by-suburb basis. It looks at land performance and ways to repair the most severely damaged land to a level that if there was a similar earthquake in the future, this remediated land would not be as extensively damaged. Consequential damage to dwellings would also be significantly reduced in these areas. The report has been developed around the targeted level of land performance that has been adopted by the NZ Government. The land remediation methods set out in the report for each suburb or area are those which can meet the land performance standard adopted. These go beyond the statutory obligations of EQC. The Stage 1 report presented the damage categorisation, mapping methodology, information and results generated to 1 October That report developed land remediation concepts and then focused on the broad range of land remediation options. This Stage 2 report provides more detail about the land remediation options T&T has been asked to further develop within defined recovery zones with specific reference to individual suburbs affected by significant land damage.

6 2 2 Recovery process For the vast majority of properties affected by the Darfield Earthquake sequence, the recovery process is relatively straightforward and repairs can begin. There are two related activities that need to happen damaged land needs to be remediated and damaged buildings need to be repaired (or demolished and rebuilt). T&T, on behalf of EQC, has looked at the land remediation process. Necessary land and building work will be determined by the private residential insurer, or (for claims under $100,000 plus GST) EQC, in accordance with council consent requirements, such as minimum floor levels. In areas where the land damage has been mapped, rebuilding can be undertaken in line with the land remediation process outlined below. 2.1 Zone A In Zone A the land has not been damaged within most properties, and therefore does not require remediation. Repairs and rebuilding of damaged buildings can begin now, but consideration should be given to the potential for ongoing aftershocks to cause further minor building damage Process EQC claim assessments to confirm no damage to land (no sand ejected, no land cracking), and Repair building on existing foundations (provided they are not damaged), or Rebuild on standard foundations subject to simple shallow soil testing to confirm that the upper ground surface provides sufficient bearing capacity in terms of NZS Programme outline The programme of building repair works will be coordinated by the Fletcher Construction Company for EQC claims under $100,000 plus GST. Building repair and rebuilding works for claims over $100,000 plus GST will be arranged through the private residential insurance companies. A flowchart demonstrating the indicative programme is provided in Figure 5.1 (page 13). 2.2 Zone B Zone B land has mostly suffered some land damage as a result of liquefaction. T&T engineers consider that this land has now mostly returned to its pre-earthquake strength, although the ground surface may be disturbed and require minor surface levelling and compaction. EQC will generally cover the cost of this surface remediation work Process Cracks located on accessible land should be filled with sand or gravel (depending on crack width) and the land should be lightly compacted with a plate compactor or small roller. Additional works may be required where cracks or significant volumes of ejected sand are present beneath dwellings. Necessary land and building work can begin now in accordance with council consent requirements. In cases where foundation repair or rebuilding works require consents, the suburb wide geotechnical reports will assist in providing engineering guidance. Repair building on existing foundations (provided they are undamaged and level), or Evaluate the practicality of re-levelling or repairing damaged foundations, and repair wherever economically practical, or

7 3 Demolish and rebuild where re-levelling or repair is not economically practical. Rebuild on new foundations, in accordance with council consent requirements, subject to simple shallow soil testing to confirm that the upper ground surface provides sufficient bearing capacity in terms of NZS Programme outline The programme of building repair works will be coordinated by the Fletcher Construction Company for EQC claims under $100,000 plus GST. Building repair and rebuilding works for claims over $100,000 plus GST will be arranged through the private residential insurance companies. A flowchart demonstrating the indicative programme is provided in Figure 5.2 (page 13). 2.3 Zone C Zone C is the land which has generally suffered very severe or major land damage, or is close to the areas of major remedial works. It includes a buffer area, where required, to provide adequate space to undertake the works and protect neighbouring buildings. Zone C also includes some areas of moderate land damage which require a wider-scale, coordinated remediation programme than the land in Zone B. Land remediation and building work in Zone C will require suburb-specific geotechnical reporting, engineering design and major remediation works. These will differ from suburb to suburb to meet the target land performance standard as adopted by the Government. Repair or rebuilding of houses in this area will need to be staged so that repairs and rebuilding work can be undertaken in association with land and infrastructure remediation Process Suburb-specific geotechnical reporting is being undertaken and will provide engineering guidance for the coordinated land repair strategies. Where buildings do not need to be rebuilt but can be repaired, cracks located on accessible land should be filled with sand or gravel (depending on crack width) and the land lightly compacted with a plate compactor or small roller. Additional works may be required where cracks or significant volumes of ejected sand are present beneath dwellings. Demolish buildings and damaged hard surfacing where re-levelling or repairing is not economically practical. Where land cracking is severe, sub-excavate the ground and recompact the upper 1-2 m to achieve a hardfill raft beneath the building platform and main access way, and as much land beyond the building platform and main access way as is practical. Where perimeter treatment works are undertaken to reduce the extent of lateral spreading under a similar sized earthquake event, building foundations can be constructed subject to simple shallow soil testing confirming suitable foundation conditions. Where perimeter treatment works are not practical, consideration could be given to constructing specific foundations that can accommodate similar levels of ground movement, as experienced from the Darfield Earthquake sequence, without structural collapse Programme outline It is recommended that works within Zone C in any individual suburb be staged to allow the maximum number of people to remain in their homes for the longest period possible. Staging of works will allow rebuilding to commence as soon as one portion of land remediation work is completed. The actual timeframe and number of stages involved will depend on a number of factors including detailed design and location of the land remediation works, obtaining necessary regulatory

8 4 approvals, and co-ordination with infrastructure works. Once each stage of the land remediation works is complete, rebuilding works in that stage will be coordinated by the private residential insurance companies. It is likely that land remediation works will occur concurrently in a number of areas to ensure the works can be completed as quickly as possible. A flowchart demonstrating the indicative programme is provided in Figure 5.3 (page 14). 2.4 Areas not covered by mapping Areas not yet covered by mapping are probably Zones A or B and are unlikely to be Zone C. For areas of land not covered by the suburb zoning maps, the normal EQC claims assessment process will apply. The EQC assessment teams will undertake an observational approach to determine whether to apply Zone A or Zone B type recovery responses. In the event that clusters of major land and building damage are encountered, EQC will advise the private residential insurers that a coordinated response may be required Process Where there is no evidence of ground liquefaction, respond according to Zone A process. Where there is evidence of ground liquefaction but no lateral spreading or flow sliding, respond according to Zone B process. On sites where liquefaction induced settlement occurred, an NZS 3604-type geotechnical investigation is required (unless one already exists for the specific site prior to the Darfield earthquake). Where there is evidence of lateral spreading and flow sliding, respond according to Zone C process. Any further mapping undertaken by EQC will be shared with the private residential insurers to ensure that the recovery process is based on zonation responses where this information is available Programme outline The programme of building repair works will be coordinated by the Fletcher Construction Company for EQC claims under $100,000 plus GST. Building repair and rebuilding works for claims over $100,000 plus GST will be arranged through the private residential insurance companies.

9 5 3 Land performance categories 3.1 Summary of categories Land performance categories have been developed based on observations of land damage across Canterbury. This was done so that the relative performance of the land across each of the suburbs affected as a result of the Darfield Earthquake could be compared. This also allows for land remediation options across each of the suburbs to be compared. The land performance categories provide a common reference point and reflect the performance of the land only. In some areas, building damage may have been significant from the shaking motion of the earthquake, although the land was not affected by liquefaction or other land performance issues. Within single suburbs some land performed well, while other areas performed poorly. Proposed remediation works within some suburbs will reflect land performance standards, in that there will be more extensive work where land performed most poorly. The different scales of land repair work are designed to ensure a better land performance standard across the Canterbury region. Hence if there is a similar sized earthquake in the future, it could be reasonably expected that land performance in the remediated areas across the region should be more consistent. Without performance level categories, it would be difficult to assess the merits of applying different remediation options to different areas. Land performance categories are defined in the following table (Table 3.1). Category 0 (dark red) represents the poorest relative performance of land under an earthquake whereas Category 9 (light red) applies to areas with little or no observed land damage. Therefore, the higher the grading (lighter colour coding), the better the land performance. Table Integrated land performance category description Damage Category Performance Category Majority very severe land damage 0 Similar proportions of major and very severe land damage 1 Similar proportions of moderate, major and very severe land damage 2 Similar proportions of moderate and major land damage 3 Moderate and some major land damage 4 Moderate and occasional major land damage 5 Moderate and some minor land damage 6 Similar proportions of minor and moderate land damage 7 Similar proportions of no apparent land damage, minor and moderate land damage 8 Similar proportions of no apparent land damage and minor land damage 9 Majority no apparent land damage 10 Note: The performance category is based on an approximately 100m by 100m to 150m by 150m area of damaged land within which remedial works would be undertaken in any one suburb. Each area selected to represent the remedial works in any one suburb represents approximately 20 to 50 houses.

10 3.2 Target land performance standard After discussion of the design options presented in the Stage 1 report, the Government instructed EQC and T&T to further develop these options for land repair. The desire was for remediation solutions that would be the least disruptive to Canterbury residents, yet would provide greater resilience and improved land performance for a future earthquake event of similar magnitude. The Government decided that the land would be repaired to a target land performance standard category of 4 to 5 (Table 3.1) and have committed to funding the additional land protection works to achieve this standard. It is noted, however, that higher performance targets may be desirable in particular areas where these engineering works will also protect public infrastructure, such as roads, water and sewerage services (which serve and protect the wider communities). This would be to provide protection to vital infrastructure such as state highways, bridges and flood protection systems. It must be appreciated that it is simply not cost-effective or even possible to completely eliminate the risk of land damage under a design level earthquake (i.e. land performance category 10). Therefore, the selected target land performance standard of 4 to 5 balances the following objectives, which the Government took into account in making the above decision. Design standards and safety: Remediating land to a standard that can provide for buildings to comply with the building code allows building consents and code of compliance certificates to be issued by local authorities for necessary repair or rebuild work. A level of land performance that achieves habitability will allow most people to remain in their homes following a similar sized earthquake. This land performance appears to be approximately Category 4 to 5 (i.e. at worst moderate with some or occasional major land damage). This therefore provides a guide as to a reasonable Ultimate Limit State (ULS) design performance target to aim for. The ULS design performance target also requires that human lives are not endangered, and collapse of the structure is to be avoided. Meeting this level of land performance standard therefore provides for the safety of residents during an earthquake event. Providing assurance to insurance companies and financial institutions: It is important that the damaged land is restored to a state where the risk of future land damage is no greater, or less, than the risk before the earthquake. This means insurance companies can continue to insure dwellings in areas that have been affected by major to severe land damage. For mortgaging finance purposes, it is also important that legal restrictions or hazard notes on LIMs and Certificates of Title are avoided to all possible extents. Minimising social disruption: Adopting land performance standards at the higher end of the scale (Table 3.1) might not only be uneconomic, it would also require more significant land remediation works. More significant land remediation works would require houses to be demolished when they would otherwise be able to be repaired. This would be disruptive to communities, by displacing significant numbers of the population and exacerbating the demand for temporary housing. It would also take more time, delaying people even further from rebuilding on their properties in areas where repairs are not feasible. Minimising social disruption by allowing people to remain in their houses where possible and for as long as possible, and by reducing timeframes for rebuilding, are key objectives of the recovery process. Enhancing future resilience: It is possible to improve the resilience of communities to land damage events, allowing them to recover more easily. Protecting infrastructure and buildings to a consistent standard aims to ensure water, wastewater, telephone and power services can continue to operate, or be rapidly reinstated, following a similar earthquake event. Where people can remain in their homes with adequate services, they are better able to cope with a natural disaster. It allows people to access established social networks and to continue life with some degree of normality while repairs are undertaken. 6

11 7 Providing equity: Living in New Zealand involves an acceptance of natural hazard risks. These risks could be due to earthquakes, rainfall induced landslips, volcanic activity, floods, marginally stable slopes or eroding cliff tops, and/or a tsunami. It is therefore inequitable to completely eliminate land damage risks in one area of the country while risks exist to varying degrees in all communities. It is also important to ensure a level of land performance equity between all communities affected by land damage in the Darfield Earthquake. A higher target performance standard may mean this is not achieved. Financial: The target land performance standard of Category 4 to 5 provides an acceptable level of risk, taking into account the above factors, at an affordable cost to New Zealand. That is, it offers the best value for money. To meet the above objectives, such as avoiding demolition of buildings that can otherwise be repaired, land remediation to the target performance standard will not need to be undertaken for every land damaged site. However, where economies of scale can be achieved and the majority of houses need to be rebuilt, land remediation methods can be introduced across property boundaries to meet the target land performance objectives. More details on land remediation options, including how they can be applied to individual districts and suburbs to achieve the target land performance standard, are set out in the following sections, and in the appendices.

12 8 4 Design options Following agreement on the target land performance standard, design options were identified for each suburb. The scale and type of land remediation in areas of land damage depends on both the observed land performance during the Darfield Earthquake, and an engineering assessment of the likely performance in a future design-level earthquake. Not all areas will require engineered land remediation works to bring them up to the target land performance level. Minor ground surface restoration and recompaction of each site as part of the repair or rebuild process will be adequate in many areas. However, in the worst affected areas, different levels of coordinated land remediation intervention will be required to achieve the target land performance standard. 4.1 Remediation options The Stage 1 report set out the broad land remediation options for liquefaction risks and costs for land repair. After consideration of these options, the Government instructed EQC and T&T to focus on a narrower range of options on a suburb-by-suburb basis. These options provide the least disruption while ensuring greater resilience for communities under a future earthquake of a similar magnitude. The probability of another equal or greater earthquake event means that the risk of similar damage in the future is about the same as other natural hazard risks for communities elsewhere in New Zealand. While the Darfield Earthquake sequence is currently assessed approximately as a one in 500 year event, the Government believes it is best to take the opportunities land remediation offers to improve the level of resilience for the communities most severely affected by this event. Table 4.1 presents the various land remediation options that could be applied to particular districts and suburbs depending on the land damage observed. Schematic sections of options that achieve the required target land performance level and that can be practically applied in a particular suburb are also summarised in Table 4.1, and detailed for each suburb in the appendices. In all cases the preferred option is to retain and repair buildings wherever possible and hence avoid unnecessary demolition of houses. The repair and replacement costs of buildings and related structures for all the options considered are equivalent. It is only the land remediation (and in some cases infrastructure) costs which vary. If an option with no perimeter treatment is selected for a suburb with very severe land damage zones, individual property owners whose land has been subjected to very severe land damage could remain on their land. However, this will require that any new building development on the land is specifically designed to accommodate or mitigate the effects of lateral spreading. Where houses are rebuilt, an option exists for property owners to elect to construct more robust foundations and provide a higher level of performance in a future liquefaction event. This is a matter to be discussed between the claimant and the private insurer. A stiff foundation system, where all the elements are tied together (such as a stiff integrated floor slab), should tolerate differential ground settlement better than the unreinforced slabs and non-connected strip footings present in many of the damaged buildings. This is strongly supported by observations in other earthquakes. This may also allow more effective and economic repair following any future liquefaction event. Differential settlement of the structure would still be expected, but damage may be reduced, and re-levelling may be more feasible.

13 9 Any option for improved foundation systems would be an option that property owners may wish to personally fund to mitigate the damage from a similar sized earthquake in the future. However, this additional mitigation measure is not required to meet current building standards and property owners will need to consider whether the additional expense is justified. New buildings which are designed with recognition of the liquefaction hazard will generally perform better than the old buildings they are replacing. This will improve the overall performance of housing stock and less building damage would be expected in a similar earthquake in the future. Options were considered for each suburb mapped for land damage. The main consideration was the performance of the land under the Darfield Earthquake, and the options available to improve the overall performance of the land where required within the identified constraints. The target land performance standard (4 to 5) has been adopted as detailed in Section 3.2. Opportunities have also been evaluated to integrate the remediation work with community and council property to bring a wider benefit to overall communities. Observations from field inspections indicate that the vast majority of buildings and land have performed satisfactorily in accordance with design code performance requirements. However, some areas will require engineering intervention to achieve the adopted target land performance standard. The appendices to this report provide more detail on the design solutions for each suburb.

14 10 Table 4.1 Remediation options Option Description Example Diagram E1 Ground treatment of the perimeter in severely affected areas only. In future events this treatment should mitigate potential for very severe to major land damage. In adjacent areas where buildings need to be rebuilt because they are uneconomic to repair, a low cost shallow dynamic compaction method could be used to create a thicker non liquefiable raft to further mitigate damage for the worst affected moderate land damage zoned buildings. E2 E3 Ground treatment of the perimeter in severely affected areas only. In future events this treatment should mitigate potential for very severe to major land damage. However, the risks of land damage (liquefaction related settlement and ground oscillation) to moderate zones remain. Ground treatment of the perimeter in severely affected areas only, to mitigate the potential for severe lateral spreading. In future events this treatment should reduce the severity of land damage from major and very severe down to moderate and some major land damage. In adjacent areas where buildings need to be rebuilt because they are uneconomic to repair, a low cost shallow dynamic compaction could be used to create a thicker non liquefiable raft to further mitigate land damage for the worst affected moderate zoned buildings. Highest Land remediation costs Greatest Reconstruction time Lowest Potential damage from another similar earthquake

15 11 Option Description Example Diagram E4 Ground treatment of the perimeter in severely affected areas only. In future events this treatment should reduce the severity of land damage from major and very severe down to moderate and some major land damage. However, the risks of land damage (liquefaction related settlement and ground oscillation) to the moderate zones remain. G1 No ground treatment. Building restriction zone may be applied to very severe land damage zones unless specific engineering design is undertaken. These residents will need to be relocated to another subdivision and the remaining land may be considered for reserve land/ parks etc, or for future development of land by others with some level of ground treatment option. G2 Minor ground treatment. In areas where buildings need to be rebuilt because they are uneconomic to repair, a low cost shallow dynamic compaction method could be used to create a thicker non liquefiable raft to further mitigate damage in future events affected in major and moderate land damage zones. This treatment is generally not considered to be an option in very severe land damage zones. Land remediation costs Reconstruction time Potential damage from another similar earthquake G3 Surface levelling and filling in cracks as required but no ground treatment. This treatment is generally not considered to be an option in very severe land damage zones without specific engineering design because ground deformation expected under a similar earthquake is beyond currently accepted design practice. Lowest Least Highest

16 Opportunities in the detailed design The detailed concept design of the most appropriate options, including the specific identification of remedial work locations, will be provided in suburb specific geotechnical reports. These are expected to be published in stages between late 2010 and early Community engagement on the limited range of options identified for each suburb is expected to inform the detailed design process. Opportunities to enhance land remediation during the detailed design process are discussed Locate engineered land remediation works within public land In many areas it may be possible to locate the engineered land remediation works within public land rather than within residential boundaries. Waimakariri District Council and Christchurch City Council have both approved in principle to locate engineered land remediation works within public land where practical. Benefits include: Protecting infrastructure: Providing a level of future protection for infrastructure that requires replacement or repair within the road or esplanade reserves (linking to enhancing community resilience and providing greater value for money as discussed in Section 3.2 of this report); Minimising delays in rebuilds: Allowing staged rebuilds of dwellings to occur earlier as works will have a lesser impact on private properties; Minimising disruption: Affecting fewer properties which allows for a greater number of people to stay in their homes and begin repairs or rebuilds as necessary. The extent to which these opportunities can be taken up in different suburbs depends on site characteristics and community expectations. Such opportunities will not be available in all areas as there is not always enough available room within public land to provide for the engineered land remediation works. A combination of works between the front yards of private properties and the public road reserve may be suitable in some areas to protect mature esplanade reserve vegetation (i.e. trees located along roads or river banks). Regulatory frameworks may also affect detailed design and location. Construction management plans will be a part of all detailed designs to minimise potential social and environmental effects of construction Setting a higher target land performance standard In some areas, local authorities may want a higher target land performance to provide protection to their infrastructure investments. This is currently being discussed with local authorities and will be integrated into the suburb specific geotechnical concept design process. Some residents may also elect to undertake additional improvement to their land on their own account.

17 13 5 Reconstruction programme For properties that have been assessed by EQC which are mapped as Zones A and B, repairs to land and buildings (including rebuilding) can be undertaken independent of works on public land and other properties in the same suburb. In undertaking repairs it needs to be recognised that aftershocks greater than magnitude 4 can still occur well into For properties in Zone C repairs to land and buildings (including rebuilding) needs to be coordinated. The reason for this is that a greater level of land remediation is preferable, and more rebuilding is expected. Accordingly, to ensure that the recovery process is undertaken as soon as possible overall, and with the least disruption in terms of people needing to be re-housed while repairs and rebuilding are undertaken, all affected parties (including EQC and councils) need to work closely together. The programmes for Zones A, B and C are set out in Figures 5.1, 5.2 and 5.3 respectively. These figures show work that has both started and scheduled to begin. It includes indicative timeframes. Figure 5.1. Indicative programme for Zone A Figure 5.2. Indicative programme for Zone B

18 14 Figure 5.3. Indicative programme for Zone C

19 15 6 Glossary Dwelling A dwelling is the word used in the Earthquake Commission Act 1993 to mean any self-contained premises which are the home or holiday home of one or more persons. Ground oscillation In areas where liquefaction occurs away from the unconstrained edge of a channel or dip, large horizontal displacements and cracks are unable to occur. However, due to the underlying liquefied material, the ground surface is able to move backwards and forwards (oscillate) during earthquake shaking. This may cause minor ground cracking and damage to underground infrastructure. Lateral spreading The most severely affected areas are where land has been able to move horizontally due to its proximity to open channels or dips. The land is unconstrained and moves towards these channels. In moving, cracks parallel to the channel can open up and the surface of the land can drop. Liquefaction Liquefaction describes an event where loose soils below the groundwater level substantially lose strength and stiffness in response to an applied cyclic force, such as earthquake shaking, causing the soil to behave like a pressurised liquid. For example, in some areas in Canterbury the pressurised soil/ water mixture has squeezed to the surface through cracks, creating sand boils, colloquially called "sand volcanoes. Liquefaction related settlement After land has liquefied, the pressurised groundwater flows out of the soil and this allows the soil to reconsolidate. Also, in many areas, some of the liquefied soil was ejected to the surface. Both of these processes result in ground settlement. Most of this settlement will have occurred shortly after the earthquake, but in some areas gradual settlements occurred for several weeks or months after the earthquake. Magnitude (M) This characterises the relative size of an earthquake and is based on measurement of the maximum motion recorded by a seismograph. Several scales have been defined, but the most common is the "Richter magnitude". Modified Mercalli Intensity (MM) This quantifies the effects of an earthquake on the earth's surface, with 1 denoting not felt and 12 total destruction. The values will differ based on the distance from the earthquake centre and other parameters such as ground types. Data is gathered from individuals who have experienced the quake, with aggregated information used to map intensity levels generally radiating out from the epicentre. NZS 3604 New Zealand Standard NZS 3604: 1999 Timber Framed Buildings is a key New Zealand Standard used by the building industry. It provides suitable methods and details for the design and construction of timber-framed buildings up to three storeys high. It applies to domestic dwellings, most residential and some commercial and other buildings. Ultimate Limit State (ULS) This is the design level adopted when designing buildings and structures buildings must not collapse when subjected to loads similar to this design level, but are likely to require extensive repair or total reconstruction.

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