If your building is potentially earthquake-prone, you will need a structural engineer to conduct an engineering assessment.
An Initial Seismic Assessment (ISA) will provide a broad indication of the earthquake rating of your building.
A structural engineer can also conduct a Detailed Seismic Assessment (DSA) of your building. This will provide is a more comprehensive assessment of the earthquake rating of your building and can include potential design solutions for seismic upgrades.
How to find an engineer
You can get help to find the right engineer for your project from the Institution of Professional Engineers New Zealand (IPENZ) and the Association of Consulting Engineers New Zealand (ACENZ).
Your engineer should:
- be a Chartered Professional Engineer (CPEng) whose main area of practice is structural engineering, with an emphasis on seismic strengthening
- have experience with buildings that have similar materials and construction to your own building — both in assessing them and structurally strengthening them
- have professional indemnity insurance
- be a member of a professional engineering organisation such as IPENZ that helps them maintain competency in structural engineering and meet current industry standards.
Questions to ask an engineer
Before you hire an engineer, discuss the services they can provide and how they will work with you. Consider whether the engineer is someone you can work with and have confidence in. The best engineering advice is most likely to come from an engineer with experience in the seismic upgrade of buildings similar to yours.
Ask about their expertise and experience:
- their experience with a wide range of structural types and materials
- their experience of working with historic buildings
- their track record with retrofitting buildings similar to yours
- the contact details of the owners of two or three of their projects, so you can check if the structural solutions suited the building and ask about the quality of service the clients received
- the quality assurance systems they use
- the staff members who’d work on your project and their levels of expertise and involvement.
Ask about their approach to the project:
- the project’s broad scope of work
- who will locate any existing documentation on the building
- will they need to prepare measured drawings and conduct testing to determine engineering properties of the materials of construction
- whether the design process will occur in stages
- the fee rates and rough order total cost to provide the scope of work.
Make sure you understand what the engineer is going to provide you with. A greater input at the concept and detailed design stages may reduce the cost of construction later on.
What your engineer will do
Your structural engineer will perform several tasks. They can conduct an initial seismic assessment (ISA) or a detailed seismic assessment (DSA).
Your engineer will let you know which assessments are required if the council have identified your building as potentially earthquake-prone.
The earthquake-prone buildings methodology provides guidance to engineers completing assessments. It also outlines the requirements for reports you’ll need to provide to your council.
The documented guidelines Seismic Assessment of Existing Buildings provide a technical basis for engineers to carry out seismic assessments of existing buildings.
What’s involved in a performing an engineering assessment
When conducting an engineering assessment, your engineer will:
- complete an external inspection of the building and where appropriate an internal inspection of the building
- consider original building plans or calculations or prepare and use assumptions if plans or calculations are not available
- consider building parts that would pose a significant life safety hazard if they lost support or fell, caused another building element to lose support or fall, or caused any section of the building to lose support or collapse
- consider whether the building has a shared structural form or shares structural elements with any adjacent buildings
- determine the ultimate capacity of the building and its parts, and the earthquake shaking demand to produce a %NBS
- 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 likely damage to other property.
What’s involved in a performing a detailed seismic assessment
A detailed seismic assessment (DSA) of your building’s current seismic capacity is usually the best basis for establishing the structural work required on your building. A DSA uses a number of standard assessment methodologies which are useful if you later decide to have the advice peer reviewed.
Depending on the scope of your project, the engineer may perform these tasks.
Reviewing drawings and existing materials
- Determining the foundation conditions and characteristics at the site of the building
- Reviewing original building plans
- Investigating the properties of the building materials, which may require physical testing
- Recording details of geometric information and construction materials on drawings and in a report for you
Investigating the building’s structure
- Identifying the actions that the building will be subjected to in its life
- Measuring and calculating the weight of the various components of the building
- Analysing the building as a whole to identify the stresses and deflections in the structural elements of the building
- Identifying the critical structural weaknesses and the collapse mechanism for the building structure
- Identifying the effect of acceleration and displacement on the main non-structural elements
Beginning concept designs, a project timeline, and rough costs
- Preparing concept designs for repair and retrofit
- Preparing rough order costs (ROC) for the concept designs
- Identifying the most critical work for earthquake mitigation or most effective return on expenditure, for completion earlier in the project
- Identifying a possible sequence of work or programme that shows the work being carried out in stages.
What you’ll find in a DSA report
After a detailed seismic assessment, your engineer will give you a report. It will set out the results of their analysis, concept designs, their costs, and conclusions. The report should include these things.
A description of the building report
- The scope of the report and its limitations
- A Building Features Report that provides a summary of detailed information
Identification of the building’s seismic weaknesses
- Description of the expected seismic activity for your site and foundation soil conditions
- Description of the building structure
- Description of critical loads for the assessment analysis including loads due to self-weight, wind, snow and earthquake
- Identification of critical structural weaknesses
The proposed solution and how it would perform in an earthquake
- How the structural solution will affect the heritage fabric, and options that maximize retention of heritage character and fabric
- A qualitative description of the damage that would probably be sustained by the current building in the event of earthquakes of increasing intensity, and associated %NBS for each of these intensities
- A qualitative description of the damage that would probably be sustained by the retrofitted building at each of the intensity levels considered for the existing building
Beginning to schedule and cost the construction costs
- The outline of a schedule of work for construction of the repair and retrofit, with associated rough order costs
- The outline of the programme of work – including a project timeline.
Check your project is financially feasible
Use the information in the DSA report to estimate whether your project is financially feasible. You’ll need to decide on a programme of work that matches the funding available.
Once a concept design and cost is agreed, the design process can proceed to detailed design.