Section 2: Engineers carry out assessments of potentially earthquake-prone buildings

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2.1 Scope for engineering assessments

This methodology sets out how an engineering assessment of a potentially earthquake-prone building is required to be carried out.

If an owner receives a request for an engineering assessment, the owner, in accordance with section 133AI of the Building Act, must provide the territorial authority with an engineering assessment or a previous assessment (refer to section 3.0 of this methodology), evidence of a factual error with respect to the building’s potentially earthquake-prone building status, or notification that an engineering assessment will not be provided (refer to section 3.1 of this methodology).

An engineering assessment must meet the following requirements:

1. the qualification requirements specified in section 2.2 of this methodology
2. the requirements for determining the appropriate form of engineering assessment specified in section 2.3 of this methodology
3. the technical requirements specified in section 2.4 of this methodology
4. the reporting requirements specified in section 2.5 of this methodology.

If a territorial authority accepts a previous assessment (refer to section 3.3 of this methodology), the owner is not required to also obtain an engineering assessment.

This section of this methodology refers to Part A, Part B and Part C of the Engineering Assessment Guidelines.

2.2 Qualification requirements

An engineering assessment must be overseen and signed off by an engineer with relevant skills and experience in structural and earthquake engineering, and assessments of existing buildings. At a minimum, the engineer that oversees and signs off an engineering assessment must be a structural engineer who is chartered under the Chartered Professional Engineers of New Zealand Act 2002.

Engineers undertaking an engineering assessment will need to be able to interpret and apply the requirements and technical methods set out in the Engineering Assessment Guidelines.

2.3 Determining the appropriate form of assessment

The engineer must determine whether an Initial Seismic Assessment or a Detailed Seismic Assessment as described in the Engineering Assessment Guidelines is appropriate for the building in accordance with the framework set out in Figure 2.

The Engineering Assessment Guidelines recommends, in most cases, that an Initial Seismic Assessment is carried out as the first step of a Detailed Seismic Assessment.

For an Initial Seismic Assessment to be used as an engineering assessment and therefore as the basis for determining whether or not the ultimate capacity of a building is exceeded in moderate earthquake shaking, the engineer must be confident that the result reflects the building’s expected seismic behaviour.

In particular, the engineer must:

1. have a clear understanding of the structure and how it will respond in an earthquake, and
2. be confident that there are no aspects of the structure that require more specific or detailed investigation and assessment; ie no potential Critical Structural Weaknesses that could lead to a %NBS that is less than 34%NBS.

Figure 2: Framework for determining the type of engineering assessment required

2.4 Technical requirements for the assessment

An Initial Seismic Assessment must meet the requirements of Part A and Part B of the Engineering Assessment Guidelines.

A Detailed Seismic Assessment must meet the requirements of Part A and Part C of the Engineering Assessment Guidelines.

An engineering assessment must:

1. include necessary inspections of the building: an external inspection of the building, and an internal inspection of the building where it is appropriate to do so.
2. consider either the original building plans or calculations; or in lieu of plans or calculations, prepare and use appropriately justified assumptions in place of information that would have otherwise been obtained from the plans or calculations
3. consider parts of buildings in accordance with the scope and definition of parts set out in section 2.4.1 of this methodology
4. consider whether the potentially earthquake-prone building comprises a shared structural form or shares structural elements with any other adjacent titles, and, if this is the case, consider the extent to which the low scoring elements (ie those scoring below 34%NBS) affect or do not affect the structure as a whole, as described in the Engineering Assessment Guidelines
5. determine the ultimate capacity of the building and its parts, and the earthquake shaking demand to produce a %NBS
6. for buildings less than 34%NBS, determine the mode of failure and physical consequence of the building or parts, and the nature of the significant life safety hazard and/or likely damage to other property.

2.4.1 Considering parts of buildings

The Building Act refers to a building and a part of a building. An engineering assessment of a potentially earthquake-prone building must consider parts of buildings as described below.

A building part is an individual building element that would pose a significant life safety hazard if it is able to:

1. lose support or fall, or
2. cause another building element to lose support or fall from the building, or
3. cause any section of the building to lose support or collapse.

A significant life safety hazard is an unavoidable danger that a number of people are exposed to.

An engineering assessment of a potentially earthquake-prone building must consider and include parts of buildings in accordance with Part A of the Engineering Assessment Guidelines.

An engineer will need to exercise judgement in applying the earthquake-prone building provisions to parts of buildings. Whether a particular building element is considered a part of a building will depend on the individual circumstances of the building and whether a significant life safety hazard is present. The justification or reasoning for inclusion or exclusion of a part should be clearly reported.

However, the consideration of parts for the purposes of assessing potentially earthquake-prone buildings is not intended to be as broad in scope as the application of the term ‘parts’ for the structural design of new buildings.

Parts of buildings likely to be a significant life safety hazard that would be expected to be included in an engineering assessment are described in Part A of the Engineering Assessment Guidelines.

2.5 Reporting requirements

The resulting engineering assessment report must be provided to the territorial authority. In addition, a summary of the engineering assessment must be provided to the territorial authority, in the format prescribed by the Engineering Assessment Guidelines. The following information must be provided in the summary:

1. a statement of appropriate qualification and experience (supplemented with any relevant training attendance) of the engineer overseeing and signing off the engineering assessment
2. the relevant building information
3. a statement of confirmation that an external and internal inspection of the building was completed as part of the engineering assessment, or appropriate commentary where an internal inspection was not completed
4. a description of the engineering methodology used and key parameters (and if the engineering assessment is an Initial Seismic Assessment, a confirmation statement that the Initial Seismic Assessment provides a result that the engineer is confident reflects the building’s expected behaviour)
5. sufficient detail about the building and any parts that score less than 34%NBS and therefore pose a significant life safety hazard to allow the territorial authority to evaluate the possible consequences of failure
6. if the building comprises a shared structural form or shares structural elements with any other adjacent titles, information about the extent to which the low scoring elements (ie those scoring below 34%NBS) affect or do not affect the structure as a whole
7. the %NBS for the building
8. for buildings less than 34%NBS, a statement on the expected mode of failure and physical consequence of the building or part, and the nature of the significant life safety hazard, and/or likely damage to other property.

The engineering assessment report and summary must be accompanied by all documentation considered in undertaking the engineering assessment or, in place of appending this documentation, a list with specific references to the documentation used. This must include the building plans, and drawings and calculations considered; or in lieu of these, an appropriate justification of the assumptions used for information that would have otherwise been obtained from the plans, drawings or calculations.