Carrying On After an Earthquake – Low-Damage Principles In Residential Construction

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Aug 07, 2019
Low damage home design NZ, best home designs in earthquakes

The Challenge

The recent earthquakes in California are a reminder that seismic activity occurs regularly around the globe. Here at Fraemohs’ headquarters in Canterbury we are all too aware of this, having lived through a series of major earthquakes that caused unprecedented damage to the region’s housing stock and commercial buildings. The resulting rebuild has brought with it huge economic and social costs.

New Zealand is an active seismic region, and it is a certainty that we will be affected by large earthquakes in the future (on the plus side, this is what gives us our amazing landscapes!). In fact, New Zealand is reportedly considered the second riskiest country in the world by insurers, according to a 2018 global insurance risk report by reinsurer Lloyds.

Locally, insurers are becoming reluctant to insure a lot of New Zealand’s building stock because of the cost of remediation after a major event, making it increasingly expensive or impossible to get cover. We now have insurers threatening to pull out of the New Zealand market altogether.

 

A Shift In Thinking…

In this context, we are seeing a shift in focus around seismic design. Historically, we’ve rightly focussed on life-safety; aiming to prevent a catastrophic collapse by designing the building to yield (sustain damage) in a controlled manner during a large seismic event, enabling everyone inside to evacuate. While this limits loss of life, it is often difficult or impossible to repair this damage. This contributes to the enormous rebuild costs, jittery insurers, and stressful relocations for families and businesses.

Clearly, we need our buildings to remain serviceable where possible after a major earthquake. The construction industry is starting to respond to this, with engineers and architects employing “low-damage design” principles in their new buildings. For commercial buildings, there are a number of strategies available to increase building resilience, such as:

  • Making the building so strong that the design limit is never reached, even in the largest anticipated event. Sounds obvious, doesn’t it? Unfortunately, the cost of this is so great that it is prohibitive for all but the most essential structures, such as hospitals and significant civic buildings.
  • Protecting a building’s structure in a significant event by using base isolators. These prevent the most significant forces from the ground from being transferred into the structure.
  • Dispersing the shaking energy throughout the entire structure and dissipating it in specially designed dampers at joints between structural elements. If there is any yielding during a seismic event, it is concentrated in these elements. They are specifically designed to be easy and inexpensive to replace so the building remains functional or can be put back into service very quickly.

 

 

What About Our Residential Housing?

The low damage design approaches above are fine in commercial projects, but are too costly in a residential setting. Our industry needs solutions also, as the residential rebuild in Christchurch has been a colossal undertaking.

In the aftermath of the Christchurch earthquakes, solid timber construction was shown to be among the best options for building a resilient home. We have always been confident of this here at Fraemohs, and it was nice to see that borne out in the stories from our clients. It turns out that solid timber construction inherently follows some of those low-damage principles:

  • Timber is strong, and also naturally flexible. It is good at absorbing energy internally (think trees in the wind, cricket bats, etc).
  • The structure naturally dissipates seismic energy as the boards move over each other, and we use ductile steel reinforcing rods to resist uplift.
  • We have seen through the Christchurch and Kaikoura earthquakes that solid timber homes have sustained very little damage to the superstructure. In cases where the foundation has suffered damage, solid timber homes also tolerate re-levelling very well.
  • In solid timber construction, there are fewer secondary elements likely to sustain damage. For example, there are no separate external claddings that can crack and fall off and there is no gib on the interior walls that can break up.

The end result – in the vast majority of cases, after an earthquake, you can just pick up the house contents off the floor and carry on living in your solid timber home.

As a bonus, you’ll be living in a stylish, warm home, that is locally made from New Zealand grown timber. Solid Timber homes really do tick a lot of boxes.

 


 

If limiting damage to your home or commercial building in the event of an earthquake is of interest to you, you can contact us to receive more information. Simply visit our contact page and ask to learn about our earthquake proof Solid Timber system.