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Posts Tagged ‘seismic’

Keep barbed wire straight and overlap ends in center of wall

Keep barbed wire straight and overlap ends in center of wall


An engineer of note gave us some suggestions on how to improve earthbag corners in seismic areas. The engineer is concerned the barbed wire could shift in a quake. He felt that wire mesh anchors (4- 5 with 1″ long teeth, bent so it stands up nicely) would better secure barbed wire at corners. He preferred the idea of running the barbed wire straight out the end of the wall, around a wire mesh strip at the corner and back into the wall. That way it was nearly tensioned. The barbed wire could also run up and over into the next course.
Wire mesh anchors can better secure barbed wire at corners

Wire mesh anchors can better secure barbed wire at corners


Related:
Reinforced Mesh Corners
Low-Cost Reinforcement of Earthen Houses in Seismic Areas
Source: Special thanks to Patti Stouter of Simple Earth Structures for networking with engineers at a recent earth building conference and coming up with these ideas, the drawing and photo.

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Seismic Resistant Gravel Bag Foundation (click to enlarge)

Seismic Resistant Gravel Bag Foundation (click to enlarge)


Yesterday’s post was about the earthquake resistance of earthbags. Today’s post illustrates what an earthquake resistant gravel bag foundation looks like and explains why this design is so effective. Gravel is an ideal material for this application because it’s durable, reasonably inexpensive, readily available in most areas, has high bearing strength and prevents wicking of moisture up in the wall. Gravel will shift or ‘give’ during seismic activity, thereby relieving stress without causing structural damage.

The gravel is contained in polypropylene bags or tubes, double-bagged for strength. The gravel bags rest directly on a typical rubble trench foundation with a French drain that removes water from under the building. Two courses of 4-point barbed wire between courses reduce slippage and provide tensile strength. Vertical rebar or bamboo pins are placed opposite each other and tied together through the wall with sturdy baling twine. Plaster mesh, fishing net or plastic fencing is tied to both sides for additional seismic resistance. Typical soil-filled earthbags are placed on top of the gravel bags once you’re safely above where moisture can cause problems.

Gravel bag foundations score highly in every category: ease and simplicity of construction, dirt cheap cost, durability (poly bags can last 500 years if protected from sunlight) and earthquake resistance. No concrete forms needed — just a few simple tools such as a shovel. I highly recommend reviewing some previous blog posts on this subject to better understand why earthbag foundations are a favorite among natural builders.
– A similar gravel bag foundation with strawbale walls successfully passed a shake table test in Nevada with forces that surpassed that of the Northridge quake in California.
Earthbag Foundations background info
Scoria or pumice can be used in place of ordinary gravel to create a frost-protected insulated foundation. (Frost-protected foundations save energy and greatly reduce construction costs because you don’t have to dig down to frostline.)
Rubble Trench/Earthbag Foundation
Earthquake-resistant Earthbag Building Details
Low-Cost Reinforcement of Earthen Houses in Seismic Areas
Another Earthbag Foundation Method explains an alternative way of building a foundation with gravel bags.
Rubble Bags
Flood and Earthquake Resistant Earthbag Foundations in Pakistan
Reinforced Mesh Corners
Earthbag/Stone Foundations

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This is another major announcement courtesy of Structure1.com. Instead of building buttresses, which tend to be time consuming and difficult to design correctly for earthquake zones, they recommend using the same specifications we reported earlier for reinforced earthbag walls in seismic regions. The comments below are from the latest email exchange with Structure1.com.

Refer to: ASTM E2392, Standard Guide for Design of Earthen Wall Building system. Please note that this empirical standard is applicable only when engineering design is not available.

Portions of the International Building Code, IBC, and ACI 530. Please note that chapter 5 of ACI allows unreinforced adobe only in Seismic Design Category A. So, it [unreinforced earthen construction] is not allowed in Seismic Design Category B, C, D, E and F. That is to say it is practically not allowed in more than 95% of the world.

If this is the case, reinforcing bars are always required. So, while buttresses add strength to earthbag construction, they are not required as long as we use reinforced steel bars. Buttresses can be eliminated to save money. The project will be more economical and comply with the building code with reinforcing steel bars only.

Once again, we owe a great deal of thanks to Structure1.com for their efforts to move earthbag building to the next level. Note: No one has received any money for any of this work! This is all pro bono work intended to help those most in need.

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The specifications for reinforced earthbag walls in seismic regions from Structure1.com describe how to attach shear walls to earthbag walls. Properly built shear walls add a great deal of strength to earthbag structures, but are seldom discussed. I thought a detailed drawing of this feature would be helpful. The drawing below illustrates the key concepts.

Attaching Shear Walls to Earthbag Walls

Attaching Shear Walls to Earthbag Walls


Shear walls resist lateral forces from wind and earthquakes. They brace exterior walls (earthbag walls in this case) like buttresses. The connection between the shear wall and earthbag wall must be strong. The drawing shows how threaded anchor bolts are embedded in the earthbags in a vertical row no more than 24” apart. The threaded ends of the anchor bolts protrude far enough to go through the stud. Tighten the nuts (with washers) before sheathing the wall. Wood or metal frame walls sheathed in ½” plywood are both acceptable.

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Reinforced Earthbag Wall Section for Seismic Areas (click to enlarge)

Reinforced Earthbag Wall Section for Seismic Areas (click to enlarge)


I am extremely happy to announce another major first for earthbag building. Precision Engineering has generously provided drawings and specifications for building earthbag structures in seismic areas to meet code. The documents have been combined into one 6-page PDF and are now available online.

Reinforced Earthbag Specifications is a 6-page PDF describing in drawings and text exactly how one might construct a reinforced earthbag wall that would pass most building codes in areas of high seismic risk. This document was prepared specifically at the request of Dr. Owen Geiger and Kelly Hart for use on reconstruction projects in Haiti, but it could be useful wherever reinforced vertical wall structures may be built. We want to acknowledge and thank Nabil Taha of Precision Engineering for his patience and diligence in preparing this document.

This document is now accessible from EarthbagBuilding.com and EarthbagStructures.com with the following disclaimer:

“The information/drawings that follow are just general and preliminary and may not be applicable to your or to any user’s particular project. Users of these opinions/information assume all liability arising from such use. You should retain the service of Precision Structural Engineering, http://www.structure1.com, or a local licensed Professional Engineer for engineering on any specific project. Precision Engineering and http://www.earthbagbuilding.com or earthbagstructures.com make NO warranty, expressed or implied, or assume any legal liability or responsibility for the use and/or application of any material shown here.”

I want to emphasize what an amazing gift this is to the earthbag building community, and to those struggling in stricken areas such as Haiti. As far as I know, this is the first time an engineer has published their drawings and specifications in this manner. It’s truly a pioneering document. There is no big industry driving this movement that can pay for tests that costs hundreds of thousands of dollars, and so we rely on expert advice to take earthbag building into mainstream use.

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PAKSBAB strawbale houses in Pakistan use earthbag (gravel bag) foundations that have passed a shake table test.

PAKSBAB strawbale houses in Pakistan use earthbag (gravel bag) foundations that have passed a shake table test.


As you may well know, the recent floods in Pakistan destroyed or damaged 2 million homes, affecting 20 million people. PAKSBAB, an NGO building strawbale houses in Pakistan, uses gravel-filled earthbag foundations to protect their houses from water damage. To date, 22 houses have been built.

In addition to providing flood protection, PAKSBAB uses earthbag foundations because they are earthquake resistant. A shake table test at the University of Nevada, Reno, simulated the devastating Northridge (Canoga Park) quake that occurred in California. According to their report, “the house survived 0.82g, twice the acceleration of the Canoga Park record. Although severely damaged, the building did not appear in danger of collapse, even at the end of the test sequence.”

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Reinforced Mesh Corners (click to enlarge)

Reinforced Mesh Corners (click to enlarge)


The idea presented here is for Haiti and other areas susceptible to earthquakes. It’s a very simple concept, but even small steps like this one can save lives.

The main idea involves reinforcing corners of earthbag buildings with plastic mesh or plastic fencing. For background information, see my previous post on Low Cost Reinforcement of Earthbag Houses in Seismic Areas that discussed the research at the Catholic University of Peru. Blondet, one of the lead researchers on the project, said plastic reinforcement mesh was the strongest method they’ve tested in 35 years of seismic research.

The main addition here is ¼” rebar to secure the plastic mesh. Add ¼” rebar and plastic mesh on both sides of the wall and tie together through the wall with baling twine or nylon cord. Bend the rebar and plastic mesh at the top of the wall and embed in the reinforced concrete bond beam. Embed it in the concrete foundation if you have one. Lower cost chicken wire or fishing net may be adequate for the remainder of the walls. There’s also a 1/2″ internal rebar pin pounded through corner bags. Note: earthbag walls in non-seismic areas typically do not use mesh unless required by code.

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Confined Earthbag (click to enlarge)

Confined Earthbag (click to enlarge)


Sometimes incremental changes are the most effective. People are naturally resistant to major changes, but they’ll more readily grasp and utilize small changes. That’s the thinking behind this confined masonry/earthbag system. Confined masonry is one of the most common building systems in the world, with millions of structures built this way.

Confined masonry construction consists of unreinforced masonry walls confined with reinforced concrete (RC) columns and RC bond beams. In Mexico, where confined masonry makes up over 60% of all structures, it is used for lowrise construction and for buildings up to seven stories high. Confined masonry housing construction is practiced in several countries that are located in regions of high seismic risk, including Mexico, Slovenia, Chile, Peru, Argentina, Serbia and Montenegro. A very important feature of confined masonry is that columns are cast-in-place after the masonry wall construction has been completed.

The drawing above shows how to mimic traditional confined masonry using mortared stone or rubble and rebar columns, with earthbags between. Make the columns with steel cages filled with mortared stone or rubble as shown. This is one good way to build long straight walls without buttresses. (Note: mountains of rubble are freely available in Haiti. This system was created to help utilize some of that waste material to rebuild the country sustainably.)

Confined Masonry Construction, by Mario Rodriguez

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Barbed Wire Anchors for Seismic Regions

Barbed Wire Anchors for Seismic Regions

Patti Stouter has devised a new way of reinforcing earthbag walls in seismic regions. Cement mortar is inserted in some joints between bags to lock the barbed wire in place and increase tensile strength. Mortar isn’t needed between every bag, and most likely every course doesn’t need this extra reinforcement. Designers/engineers could strategically place the mortar only where needed. For instance, analysis might lead to reinforcing the joint on each side of each corner and the middle of each wall on a moderate sized house. This system is very efficient — each joint would use just one shovel of mortar. One option is to tie or cinch the lower and upper courses of barbed wire together (only where mortar is being applied) to better embed the wire and increase strength. You could also mound a little extra mortar on top to add additional strength.

Designers and engineers now have another very good technique to add to our ‘tool box’ of reinforcing earthbag buildings — none of which were available or published just a few months ago. Thank you Patti.

Image credit: Patti Stouter

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