Dear Professor McCabe and Director Trotz:
Will the University of Toronto provide critical technical help with a sustainable, flexible and low-tech construction system Haitians want for small buildings?
Since the earthquake Haitians are investigating low cost but reinforced building methods. Many are using earthbag walls in their own style of buildings. This geo-textile material offers excellent thermal properties, is simple to learn, and costs about 1/4 as much as concrete block to build. Experiments to date show unreinforced earthbag is much stronger than adobe and undergoes deformation without collapse.
Reinforced earthbag is much stronger, but needs more structural testing. Research on sand bag walls have laid ground work, but cohesive fills and reinforced plasters must be tested.
I have designed and advised and done site planning for Haitian buildings ever since I completed a study of Haitian building styles after the quake.
I won first place in the jovoto $300 house competition because I listened to Haitians, and combined earthbag lower walls with an innovative lighter weight upper walls. A new Haitian school for sustainable development is eager to be involved in testing programfor these materials, cooperating with US universities.
I attach a 2 page description of the research needed for earthbag as I see it.
Engineers at the University of Delaware are interested. I am seeking other research partners and grants to make safe reinforced earthen buildings a reality in Haiti in the near future.
Thank you for any advice or contacts you can give me.
Simple Earth Structures
Building and Site Design for Warm Climates
Holmes, NY 12531 ph: 845-855-0150
...They will build houses and dwell in them; they will plant vineyards and eat their fruit...
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SEISMIC EARTHBAG PROJECT RESEARCH NEED STATEMENT
Patricia Stouter, Simple Earth Structures
July 19, 2011
Earthbag construction is a low-tech earthen building technique which is extending sustainable building beyond traditional adobe regions around the world. It has become popular because it is low cost, requires low skill levels, and has potential to resist earthquake damage better than other earthen materials. Non‐decaying polymeric bags or tubes are filled with local, natural subsoils. The bags are then stacked like large bricks to form walls and tamped for strength. Typically, barbed wire reinforcement is used between the bags or vertical reinforcing steel is driven into them for additional structural strength. Earthbags are typically covered by stucco or other plaster to protect the bags from ultraviolet decay. As with adobe, the plaster also strengthens the wall.
In a recent informal static shear test by Simple Earth Structures of a 1.2 x 1.2 m wall under diagonal compression, plastered earthbag with barbed wire had the same peak strength as a larger unreinforced adobe wall panel test referenced by the authors of the influential New Zealand Earth Building Standards(1). This panel was constructed of low-strength cohesive soil fill and low-strength lime and earthen plasters as a lower boundary of earthbag wall strength(2).
Earthbag buildings are often designed based on conventions successful with adobe. Earthbag walls, unlike adobe, usually do not collapse even when severely deformed. Reinforced earthbag walls have an elastic behavior to stress that may allow them to dampen vibrations. Using engineering strength formulas based on stiffer masonry construction may actually create less safe buildings. The increasing demand for their use as low cost buildings in seismic risk regions (like Haiti) makes better structural understanding vital.
PHASE 1: PRELIMINARY PROOF TEST
A preliminary test will validate the potential of earthbag with cohesive fill. This test will find the cyclic shear strength of a reinforced 1.8 x 1.8 m wall panel, similar to the testing used as a basis for New Zealand’s standards. A wall of high-strength (clay-rich) earthen fill with barbed wire will be built with vertical rebar reinforcement at each end and chicken wire mesh in low-strength lime plaster, following standard earthbag construction practices. This wall will be well tamped and cured before plastering.
The result of this test will be compared to the strength standards for reinforced adobe in the New Zealand documents, to provide a preliminary comment on how engineered earthbag walls might compare to adobe for medium and high seismic risk regions.
PHASE 2: STATIC BEHAVIOR TESTING
This next phase of research will compare reinforcement techniques to select the most effective low-cost techniques for simple structures using cohesive fills. Focus will be on practical information relative to small building design.
Different earth fills will be evaluated in tamped, cured bags for compressive strength to confirm a simple method of determining whether a fill meets ordinary (75 psi) or special grade (250 psi) as per NZS 4298- Materials and workmanship for earth buildings. Pull-out tests of barbed wire will be performed on cured earthbags under loadings that approximate the vertical weights present at wall elevations subject to buckling in adobe structures. Variables will include high and low tensile strength wire and mortar anchors.
Large scale shear box tests will also be performed using multiple 80% scale bags to establish friction coefficients of earthbags with barbed wire and with added wire mesh pins, using a variety of cured, tamped fill materials.
SHEAR STRENGTH OF WALL PORTIONS:
In-plane cyclic loading tests will determine the most effective reinforcement to resist pullout, compression, and other earthbag sideshear failure mechanisms for bracing walls. These will be conducted on plastered 80% scale bag wall portions of 1.1 m x 1.07 m height(3) to compare the following effects:
* Mortar anchors and wire mesh pins attaching barbed wire between bags
* Plaster reinforcement: chicken wire, wire mesh, plastic traffic fence, and plastic fishnet
* Sloping bag courses 18 degrees from vertical
* Pre-tamping and tamping bucks to compress unconfined bags at corners and openings
Full scale in-plane loading tests of 2.4 x 2.4 m wall portions will be completed of the strongest and most economical reinforcement configurations. All testing will explore structural failure as well as serviceability limits.
FLEXURE STRENGTH OF WALL PORTIONS:
Out-of-plane loading tests on 1.8 x 1.8 m walls will compare reinforcing solutions to resist wall-buckling failure mechanisms.
* Height to wall thickness ratios: 1:6, 1:8 and 1:10 ratios
* Vertical rebar position and attachment: inserted in the center or paired at the exterior
* Vertical rebars through stabilized bags in an unstabilized earthen wall
* Horizontal bracing strips of geo-grid or wire mesh anchored between courses at high stress elevations
Full scale 4 x 2.4 m height walls with returns will be constructed to test the most successful reinforcement types for low risk, moderate risk, and high seismic risk. A public report will comment on non-engineered earthbag design guidelines currently in use.
PHASE 3: DYNAMIC BEHAVIOR TESTING
This phase of the testing will evaluate optimal earthbag wall types from Phase I testing in terms of stability performance under horizontal loading using shaking table tests. 80% scale bags in 3m x 3m height walls with clamped returns will check these details:
* Base isolation or damping mechanisms from a base of gravel bags, rubber tires, or sand bags
* Superior corner strength from piers, buttresses, rebar, or mortar anchors
* Specialized reinforcement above doors and windows
Finally full-scale structures will be tested under extreme earthquake loading conditions to guide reinforcement recommendations.
PHASE 4: GUIDELINE AND PROTOTYPE DEVELOPMENT
Simplified guidelines will be prepared for non-engineered buildings in different seismic risk zones. One set will focus on buildings in the developed nations and a second set on less costly methods for other areas. Both will be free of charge on the internet(4).
These will be tested in at least two developing world demonstration projects, and revised. Instructional materials will be developed, and a system of suggested worksheets for remote and local mentoring of novice builders.
Prototype plans for several types of buildings will be engineered for high seismic risk regions and provided free of charge as well. These will include a health clinic, a two-story residence, a multi-family courtyard residence, and a modest school building.
A preliminary design guide will be written for the use of earthbag building designers, architects, and engineers, including discussion of tested strength values and suggested topics for further research.
1 The 2010 ASTM Standard Guide for Design of Earthen Wall Building Systems recommends New Zealand’s earth building standards for engineered design of unstabilized earthen building walls; NZS 4299: 1998- Earth buildings not requiring specific design; NZS 4297:1998- Engineering design of earth buildings; NZS 4298: 1998- Materials and workmanship for earth buildings, at http://www.standards.co.nz/default.htm. Information is at http://www.dab.uts.edu.au/ebrf/research/earthbuildingstandardnz.pdf
2 More information at http://earthbagbuilding.wordpress.com/2011/07/17/earthbag-shear-test/
3 Smaller bags are easier to handle, and comparable to University of Bath tests http://www.earthbagbuilding.com/pdf/croft.pdf.
4 More complete than: http://www.simpleearthstructures.com/resources/EB%20Building%20in%20Humid%20Tropics%202.pdf