Seismic restraint – there’s still a lot of work to be done nationwide
At BVT, we now have more in-house NSBE seismic experts than many of New Zealand’s largest firms. This specialisation experienced rapid growth after the Christchurch earthquakes and is making headlines again in the wake of findings from an MBIE and EQC assessment of commercial buildings across Auckland and Wellington. There are a few different reasons behind the importance of seismic restraint, most importantly the risk to life safety.
An assessment by the Ministry of Business, Innovation and Employment (MBIE) and the Earthquake Commission (EQC) undertaken in 2016 surveyed commercial buildings across Wellington and Auckland, finding that most failed to meet the standards designed to keep people safe from falling objects during earthquakes. In fact, 100% of the buildings surveyed in Auckland failed to meet the current standard and 73% failed in Wellington (Stuff.co.nz).
Seismic restraint ensures that non-structural elements such as ceilings, walls, cable trays and HVAC ducts are sufficiently braced to the building structure, to minimise the risk of them collapsing during an earthquake. Seismic engineering standards have been under intense review since the 2011 Christchurch earthquake with robust amendments made to the original 2004 standard in 2016.
Modern buildings are all designed at a structural level to withstand a certain amount of seismic action. The methods for analysing the seismic response of structures are well developed when compared to the methods for analysing the non-structural elements attached to the structure, the area explored in the assessment. The first and foremost reason for restraining non-structural elements is life safety. As we learn more about how non-structural elements respond to seismic actions through research and experimentation, it remains an important task to do our best to make sure these elements don’t pose significant risk to life during and after an earthquake.
The second reason for ensuring all components within and on the outside of buildings are effectively restrained is property loss, or cost/time to repair. Research out of the USA shows that non-structural elements typically account for more than 50% of the capital investment of a new building, with the rest made up of the structure and building contents. This means that even if the structure of a building survives a moderate seismic event without significant damage, if the non-structural elements weren’t designed for seismic performance, it could be economically feasible to write the building off due to the cost associated with replacing the non-structural elements only.
Another aspect of the economic considerations is the lost revenue due to buildings rendered inoperable for extended periods for repairs to non-structural elements. A prime example of this is extensive water damage caused by automatic fire sprinkler systems when damaged during a seismic event. Building contents stored in large volumes such as on pallet racking has also been shown to cause large economic losses due to the structural inadequacy of the racking itself.
Our team covers the seismic restraint of commercial buildings nationwide. Please feel free to contact us directly if you have any questions regarding the seismic needs of your project.