More testing info from Patti Stouter:
What’s so important about New Zealand’s earth building standards? Well, no one else has based earth building guidelines on so much testing. And recently earthquakes in New Zealand (including a magnitude 7.1) proved how well these standards keep buildings safe. Engineers visited 14 adobe and rammed earth buildings to see how well they survived. Since earthbag is a masonry technique that has similarities to adobe, their 10 page report should be of great interest to all earthen building designers.
Earth buildings that used construction techniques recommended by the standards fared well despite experiencing peak ground acceleration of 0.5 – 0.65g or more. Some historic rammed earth buildings with less reinforcement than the standards requires also survived. Earth buildings (wisely built) have been proven strong enough. But photos of the repairs needed for some buildings where construction details were weaker than the standards require can teach us a lot.
Tempted to stretch those pier spacing guidelines? Want to put just one window closer to a corner? If you’re designing for an area at risk for earthquakes, these photos may be a needed dose of reality.
Earthbags may absorb vibrations better than adobe and rammed earth. The barbed wire sunk into strong clay bags may provide more strength. But we don’t know this for sure yet. When we do know, then educated designers can use or adapt New Zealand’s earthen building guidelines to the unique strengths and needs of earthbag.
What’s the weak point of the New Zealand earth building standard? The author of a blog called The Well Run Dry pointed it out clearly in his July 1st post called ‘The Sound Foundations of Engineered Earth Construction’. Although strong earth buildings are a matter of survival in the third world, ‘Many of the publications from First World sources on the topic of earth construction are behind paywalls.’ Simpler guidelines developed for India and Colombia and Japan are available freely on the internet. But New Zealand’s guidelines help with the difficult size and construction detail decisions needed for anything beyond a minimal 2 room house. The NZS engineers have shared some test values and some construction details in several free papers on the web. But New Zealand’s three guidelines cost $100 each even in PDF form.
With unique earthbag testing results, can we craft some guidelines for earthbag that use information similar to parts of the NZ standards? I hope so. Perhaps earthbag won’t need as much reinforced concrete in bond beam and footing as the NZS recommends, at least in low and moderate seismic risk regions. But charts of bracing wall lengths needed for different wall heights and support wall spacing would help earth builders everywhere. And my goal is to make needed information freely available.