Q1. What is seismic restraint?
Q2. Why is seismic restraint of non-structural building elements Important?
Recent seismic testing conducted on the non structural elements within random buildings in New Zealand resulted in a failure rate of 95%1. Building services and other non structural elements can represent up to 70% of a building’s value 2. As these components traditionally lack seismic restraint there is potential for significant financial loss –
All new buildings require seismic restraint of non-structural elements to gain building consent, prevent future loss of life, injury and financial loss
Figure 1. Earthquake damage to non-structural elements
Q3. What non structural elements require seismic restraint?
Non structural architectural systems such as partitions and suspended ceilings also require restraint. These systems are excluded from the scope of NZS 4219, therefore to meet the requirements of the NZ building code a specific bracing design is required that is capable of withstanding an earthquake of magnitude determined in accordance with NZS 1170.5 – Earthquake actions.The way that the magnitude of earthquake acceleration is determined is discussed below in Q4.
Q4: How is an appropriate level of restraint determined?
A: There are several factors involved in determining a level of seismic restraint, these are:
The level of restraint required for individual elements is based on the importance level of the building, and the risk each element poses to safety within the building. The component categories are P1-P7, with P1 requiring the most restraint, and P7 the least. Part categories and their criteria are presented in the table below.
|Hazard to life outside the building||P1|
|Hazard to a crowd of greater than 100 people within the building||P2|
|Hazard to individual life within the building||P3|
|Component necessary for the continuing function of the evacuation and life safety systems within the building||P4|
|Component required for operational continuity of the building||P5|
|Component for which the consequential damage caused by failure is disproportionately great||P6|
|All other components||P7|
The part category and Importance level sets an expected level of performance of each component under earthquake actions.
Q5. What does seismic restraint involve/ how are components braced?
Figure 4 – Seismic restraint for suspended ceiling
Q6. When is seismic bracing design of non-structural elements required?
During the base build stage of construction, large non-structural elements will be installed and braced. Further bracing design by a seismic design specialist may be necessary at this stage due to variations from the design for consent.
The Fit Out stage of construction often involves further design by a seismic design specialist, either due to discrepancies encountered during construction monitoring, variations from the design for consent, or most commonly, due to interactions with installed services and other bracing for non structural elements.
Q7. Who is involved in restraint of non-structural elements?
Seismic design specialists then determine and design the seismic bracing requirements for individual components. The seismic design specialists issue a Design Producer Statement (PS-1) for submission to the building consent authority, recommending an agreed level of construction monitoring during installation.
Seismic design specialists can also provide a Design Review Producer Statement (PS-2) for a design prepared by another party, certifying that the design complies with the relevant standards.
During installation, the seismic design specialist provides an agreed level of Construction Monitoring. Upon completion of the work, the installer should provide a Construction Producer Statement (PS-3), certifying that the installation has been completed in accordance with the seismic specialist’s design. The seismic specialist will then provide a Construction Review Producer Statement (PS-4) certifying that the installation has been completed in accordance with the design and any other relevant requirements of the building consent authority.
For additional information visit the BRANZ seismically resilient non-structural elements fact sheets: http://www.branz.co.nz/non-structural