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Structural considerations for building in a Seismic zone  RSS feed

 
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Hi there



I am planning on building a Superadobe 36' Diameter roundhouse in The Philippines.
My question is regarding reinforcement necessary for a seismic zone and quality of soil for this.

Should the Rubble Trench Foundation suffice rather than a concrete beam)? Does any extra form of pinning need to be done apart from the normally recommended rebar Pins going in at window sill height and Concrete beam height (overlapping)  to  counter possible Seismic events?

Also I have been reading recently that either concrete or Lime stabilization in the soil  would be advantageous in seismic regions. Do you feel this is necessary? The soil I will be using here is a limestone road base that is used everywhere for foundation of roads and floors. So I'm not sure whether the Lime or concrete stabilizer is necessary.
There is conflicting information out there. Thanks  Peter
 
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Location: Bendigo , Australia
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I have has some experience with this issue.
Much experience was gained from work done in Chile, and whilst I have not yet researched it again for you, it is out there.
Essentially the issue of design is to make sure the building just does not collapse at the first shake from the ground.
A concrete ring beam around the top and even mesh on the sides were used to slow the building collapse down.
Giving people time to get out.
As for admixtures to soil. you should use the term cement, not concrete.
Concrete is a mixture of sand aggregate and cement.
Lime or cement can be added to soil in small amounts, but it is best to make samples first to find out the ratio that will work.
It may be less than 5%.
 
John C Daley
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Search this - building abode in siesmic areas

Here is a booklet written about the subject manner
Building in Earthquake zones
 
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Location: Vilonia, Arkansas - Zone 7B/8A stoney, sandy loam soil pH 6.5
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Good link John. The first things to understand about building in earthquake zones are 1. a building that is rigid and unable to move with the earth below it will fail. 2. strong, reinforced walls on a base that allows the structure to move around at the base will most likely resist failure.

The number one reason buildings fall down in an earthquake is that the building builds up a vibration due to the earth movement at the foundation and the taller the building the more pronounced the vibration movement will become.
Most of the recent tall buildings have "sliding" foundations and longitudinal vibration/movement dampers built into their core area, the idea being that the dampers will reduce the movement caused by the vibration of the earth below (it works in japan and other countries with sky scrapers).  

If you look at most of the earthen buildings that are in earthquake zones, they have thick walls sitting on a gravel trench foundation.
 
Peter Murphy
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Thanks John,

It's interesting that you mention the mesh on the walls as providing extra strength. I have read that either a wire (chicken mesh) or even a plastic version will help w the strength of the wall.
Some research suggests this, others don't. Do you have any knowledge as to whether a chicken wire or a plastic type mesh would be more effective?
Obviously I need to do some soil testing here to see what my best options are.
Appreciate  the correction of the Cement/Concrete...slip of the tongue and also for the link to the Adobe link.

The challenge of course is getting the building permit here and getting them to realize that not everything needs to be built w hollow block and cement.They are very new to this type of building here though
there are a few other examples of EarthBag homes in The Philippines.
Thanks again!
 
John C Daley
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When I spoke of mesh, I should have been more descriptive.
There are many styles of mesh and most of us consider mesh to be steel bars welded into squares or even fencing mesh which of course is flexible.
The article I refer to speaks of mesh created by bamboo strips.
Essentially the 'mesh' prevents the adobe wall from exploding outwards and allowing the roof to drop.

=You will also notice in that manual that large open spaces are not encouraged, so that large roof beams cannot fall down and injure people.
BUT remember that manual is written for a country where large rooms in homes are probally rare.
More research will help.
So what is the deal, have you drifted in and want to build something the locals cant get their head around?
Do they have fixed ideas about building?
Will they only consider pole construction?
 
Hey, sticks and stones baby. And maybe a wee mention of my stuff:
5 Ways to Transform Your Garden into a Low Water Garden
https://permies.com/t/97045/Reduce-garden-watering
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