Structural considerations for building in a Seismic zone

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

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%.

Search this - building abode in siesmic areas

Here is a booklet written about the subject manner
Building in Earthquake zones

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.

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!

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 John,

Thanks for your reply again..
The whole mesh thing seems to be contradictory to a certain extent. Conflicting messages from a variety of sources.So I will keep researching!
Even the use of some type of mesh to allow plaster (cement,cob,lime etc) to adhere to the PP walls,  seems to have differing opinions from people regarding whether you need to use them or not.
Certainly a different concern as to whether you should use a mesh to reinforce walls for earthquake considerations.

[color=cyan]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?

Yeah its an interesting question!  Over here in the Philippines everything is Cement and Hollow block (often poor quality) 4" and 6"  versions (mainly the 4" version is used to cut costs) ...all the roads are built from cement, many of the original roads they build up to a higher level cos they flood so frequently( more so in Manila than here) always done w about a 6" layer of cement...imagine how much cement that is!
But here on the island everything, houses, fences is built from 4" hollow block.

So yeah their ideas are fairly fixed. I have lodged my plans with a City Engineer and he seems open to the idea. Once the CAD plans are finalized , the permit process begins which apparently happens very quickly compared to what us Aussies are used to! He seems to feel it wont have any problem getting approved, but we will see! Even though I am going to be doing the build myself with local help, the Builders I have spoken to here seem quite open to the idea and once it's explained to them, they seem to understand how strong it would be considering the recent earthquakes experienced here in Bohol a few years back.
The biggest issue for people here is the foundation. They don't get the RTF and think concrete foundation is the only way to go. I suppose you can't blame them for that.
So from what I can tell, it should be approved and I strongly believe that there will be a lot of interest in the build once it begins. the Engineer doing my CAD drawings is keen for me to get started and just from a personal interest point of view, wants to come over and see how it's done!

So I should have my permit in a couple of weeks, maybe a bit longer!
Which part of Bendigo do you live in?

Peter

A rubble trench is your best insurance, because it will absorb the energy and provide a zone for  random movement vs the house itself crumpling.
Keeping the building to just 1 or so stories help. A ring at the top for the roof helps and a ferrocement shell (chicken wire mesh+'strong stucco plaster') will weather proof it and also help earthquake stability.

[tt]sbengi[/tt][tt]bryant redhawk[/tt]To Bryant and S

Thanks for your thoughts on the Rubble Trench Foundation. Very re-assuring  as concrete is all the go here.
Appreciate your comments!

Bryant, can you please expand on the dampers in the core and what you mean by that.Thanks!

S, can you advise on your experience building w Chicken wire mesh and how you used it? I have read about a couple of different methods of using strips of chicken wire mesh both vertically and horizontally to form a grid pattern and also Bamboo installed vertically and horizontally on internal and external walls.  I have read some really good research that also promotes using a Geo Mesh (same as what you would use around your Rubble Trench Foundation. Very interesting how it adds strength to walls.
Any thoughts would be appreciated!

Thanks  Peter

Peter, never use cement based products with earth, you will have moisture issues.
If you read the notes, the mesh is a containment system to ensure if the building is going to fall apart, it takes long enough for people to get out. The mesh stops whole sections dropping away,
giving a longer exit time.