10/21/96

COB CODE PROJECT UPDATE

For me 1996 has been a busy year. In the midst of normal everyday needs of family and making a living I did manage to make a bit of progress towards the goal of getting cob into the building code.

Attached is a copy of COB CODE PROJECT which I wrote last December. This was presented to a meeting of the SFAIA codes committee at that time and it was received with what I have since come to realize is the normal mix of WOW, skepticism, and rejection. Nobody on that committe has bothered to call me back.

Also attached is a short article about why a cob code is needed. This is due to come out in the next issue of the CobWeb newsletter.

This spring I ran a booth representing Cob Cottage Co. at the Grand opening of Real Goods in Hopland, Ca. The publics reception of cob at that event was very enthusiastic with only a small percent of folks with looks off "what planet did you come from ?".

Also, during this past year I have been able to communicate with a few structural engineers and architects specializing in earth and/or natural building and have come up with the following thought extensions to cob building and the Cob Code Project paper:

David Murphy, a structural engineer working out of San Francisco on viewing Penny Livingston's project in Pt. Reyes was concerned with what he perceived to be a lack of shear capacity on the window filled South facing wall. This wall consists of two curved segments separated by a door and with narrow cob piers between the several window openings and the door. David's premise is that these narrow cob piers will not be strong enough to resist earthquake forces and thus create a "weak side" to the building which could lead to rotation and seismic failure. He recommended that all cob buildings in earthquake country be balanced and have a wood or concrete top bond beam to give rigidity to the top of the building.

Fred Webster, a structural engineer in Palo Alto, Ca., works with adobe and is involved currently in a project to write a rammed earth code for Sonoma County, Ca. Fred has written an article on "Adobe Codes" a copy of which is attached, Fred made these comments on the Cob Code Proposal: It's ambitious and covers more than required: The rupture test should be done from the side instead of downward - this is to keep the gravity load of the test sample mass from effecting a test result of less than the actual rupture strength: Testing should be done within an accepted ICBO format to assure that the pre-code testing results can be acceptable for ICBO review of the code proposal: Ouality control will be the big issue with building officials (this might be dealt with by having the code require a minimum material strength ). Fred estimates that an approximate material strength of 30 psi will be what is needed to meet Zone 4 seismic strength requirements (see Freds article for the seismic zone map of the USA).

Bob Bruce is a structural engineer in Emeryville, Ca., and is the editor of a report for the State of New Mexico about seismic issues regarding alternative building methods. Bob feels that some important issues regarding the seismic strength capacity of cob are: shear strength: post elastic behavior; a means of controlling cracking: using thick walls so they don't fall over when they crack from seismic forces and using mesh in the wall to keep it together, We discussed the use of straw and other possible fibers in the wall and Bob put forth the notion that the development length of the fibers is an important factor worth studying. That is to say that a fiber length in excess of a balance between the earth mixture's ability to grasp the embedded fibers and the actual tensile strength of the embedded fibers is not needed. If we can figure out how strong a given fiber material is and balance the fiber length to the earth's ability to grasp it, anything longer may not add to the strength of the wall. (This potential for using a shorter fiber length might prove worthwhile in a search for more efficent and or mechanical means of mixing cob). Bob suggested what he called the $1.98 test: making a series of small three inch cube samples of cob containing different possible fibers. These could be smashed with a hammer and would tell right away if some fibers are more promising than others. For the actual cob code testing procedure he suggested using an ASTM test protocol to assure acceptability of the test results. Bob estimates a material strength of appx. 10 psi may be what is needed to resist an eight Richter earthquake (Zone 4 maximum).

Miles Allen, a New Zealand architect working in earth building, had this to say, The cob buildings in New Zealand that have with stood earthquakes are those that are well built, well connected (continuity of structure), and well maintained, The foundation should serve to protect the wall from RISING ground moisture. The straw in the wall acts a fiber to assist with stiffness but not as a structural reinforcement. In fact, the straw, pine needles, tussock stems, etc provide irrigation channels to allow the water to leave the earth wall evenly thus reducing shrinkage and significant cracking. Miles is currently involved in a project to write three earth building codes to cover five forms of earth building. Correction for over drying sounds tricky, Determining exact percentages of soil constituents is not necessary "this isn't rocket science!". Reinforced earthwall panels six feet square by eight inches thick have been shear tested in New Zealand with excellent results, A possible construction method would be to tie a bond beam on top of the wall to the foundation with sleeved and tensioned Vertical rods in the wall at four feet on center. This would act to tie the roof diaphragm to the foundation. Shake table testing will be very expensive, it might be better to collect smaller bits of data from tension, shear and compression strength tests and extrapolate. An alternate to a shake table would be a simple swinging tilt table to simulate % of gravity lateral (sideways) loads. Relative testing of exterior wall finishes could be done With a simultaneous series of wall panels exposed similarly for a period of 10 to 15 years. An important cob variable is the moisture content: before mixing, at placement, and in service. Miles finishes to say that code writing is not for the faint hearted.

An aside is called for here to point out what is obvious from the above, to wit: These folks and others not mentioned are all experienced experts in earth construction and structural engineering and they at present do not agree about such critical issues such as required material strength and the need/function of straw (fibers) in the cob. This just further points out the need for a well designed test program to give solid information based on fact as to exactly what we can expect for cob and how it can best be used to construct buildings.

Recommended reading for those of us who really have our minds in the dirt: Earth Construction - A Comprehensive Guide, by Hugo Houben and Hubert Guillard, Intermediate Technology Publications, 103/105 Southhampton Row, London WC1B, UK. ISBN 1 85339 193 X. Can be ordered thru Builders Booksource in Berkeley, Ca.

On the funding side of things. I have gathered in preliminary info on a few foundations that may be interested in funding work towards a cob code. The next task will be to write inquiry letters for funding tailored to the goals of each foundation, If any of these are successful, then a full application with proposal will be needed. To be eligible for funding a non-profit fiscal sponsor needs to be found, To this end I have contacted a couple of possible umbrella organizations but as of yet have no commitments. This all takes time and energy, So far I have been working pretty much alone on this project. If you or anyone you know are interested in joining the pursuit of making cob accessible to the millions of people effected by building codes, then please contact me.

Thanks and cob on!

John Fordice

MAKING THE BUILDING CODE WORK FOR COB

The Uniform Building Code (UBC), used in most areas of the Western United States, does not currently recognize cob as an approved method of building. Consequently, to get a building permit, anyone wishing to build with cob in areas governed by the UBC must either ignore the code or shoehorn their cob design into something that is not cob. This situation also holds true in most areas in which other building codes are in force. Avoiding the building code may Work for some cob builders, For millions of other potential cob builders. avoidance is not an option. The code is a barrier between these people and what they wish to build. This is a problem that must be solved if cob is to become a widely accepted means of building.

The solution is obvious: CHANGE THE CODE!!!!

The best way to do this, to change the code and make it work for cob, is to create a new section for the cone which deals specifically with cob. This will allow building departments to use the code to recognize cob and deal with it on the basis of what it actually is. There is a process for amending the current code that is available to anyone. One simply submits a proposed code amendment to the ICBO. All such amendment proposals are reviewed in an annual process, and if the claims made or implied by the proposed code change can be substantiated, the amendment will be accepted, and will become a part of the next published code (new editions occur at approximately three-year intervals). The key to success is the ability of the proposal to survive the scrutiny of the review process.

To write a new cob section for the UBC, a program of basic research must be undertaken. Cob as a structural system needs to be subjected to a rigorous series of accurate tests which measure the nature, strength, and performance of cob as a building material and technique. A set of realistic cob construction standards with hard data to back them up can then be developed and used to form the basis of a reliable and believeable cob section for the UBC. The purpose of this testing will not be to negate any of the hard-won empirical knowledge about cob we now have, but rather to put measured truth to it. Nor will such testing deny the spirit and magic of cob. It will simply deal with the hard fact that when cob can be factually shown to withstand the various forces that affect buildings it can then be accepted into the building code.

For a cob testing program to be acceptable to code authorities it needs to be done within a sanctioned testing facility. Adequate funding is critical to making this happen. A relationship with a nonprofit organization interested in helping make a cob code happen needs to be established. sources of funding need to be found. I have drafted a PROPOSED COB TESTING PROGRAM as a beginning vehicle in the search for funding. Can you help to make this happen? Do you know of possible funding sources that would be interested in cob or sustainable natural building? Are you or do you know of a structural engineer or building official who is interested in earthen construction? Or do you know any other people who might be interested or want to help? If any of this speaks to you and you would like to become involved please contact:

COB CODE PROJECT
c/o John Fordice
1828 Fifth Street Berkeley, Ca. 94710,
(510) 549-1033 phone/fax

Thanks and keep cobbing!

12/5/95

COB CODE PROJECT

ABSTRACT of:

PROPOSED COB TESTING PROGRAM

(a working document)

The following paper is a beginning draft proposal for a program of testing and code development for Cob Construction. The proposal starts with a brief introduction that speaks about some of the pressing environmental and political issues which face us both as members of an influential culture and as professionals involved in the creation of buildings.

The second part presents a short picture of cob as an enduring historic resource: a means of earthen construction that has shown an ability to withstand earthquakes; and a way of building which is reemerging into our present world of construction.

Part three discusses why a building code for cob is important. If Cob is to again become available as a building technique, a standardized code which is true to the actual nature of earthen construction will benefit all who wish to build with it.

Part four talks about how our present understanding of cob is for the most part based on empirical knowledge. A structure of proposed steps toward a cob code is put forth.

Part five is an outline of goals for a prescriptive cob construction code. This consists of a listing Of what currently seem to be the critical issues which both the cob builder and the building official will need to recognize. A short acknowledgment of the need for a Performance code is also included.

Part six is an outline of the main goals of the proposed program of cob testing. The intent of this goal structure is to the list the various types of information that will need to be gathered about cob in order to develop a realistic code.

Part seven is a description of the actual testing to be done. The various tests are intended to provide a clear and quantifiable picture of how cob can be expected to perform as a building material. A short description of each test is included along with the goals of each individual test, and now that test is intended to relate to the succeeding tests. The last part is a listing of the variables which can effect a cob construction project. This list is included last in this paper because it is long and perhaps daunting if one is not familiar with cob. It is long because I have attempted to be thorough and not miss anything. However it is worth stressing that cob is really a very simple and easy way to build, and once someone gets their hands in the mud, most of these variables become self evident. Cob is very flexible and an exciting sense of discovery can be found in working with this wonderful sticky material.

COB ON!

COB CODE PROJECT PROPOSED COB TESTING PROGRAM (a working document)

CONTENTS:

1. Introduction
2. What is Cob
3. Why a Cob Code
4. How to create a Cob Code
5. Goals of a Cob Code
6. Cob Test Goals
7. A Proposed Cob Testing Program
8. List of Cob Construction Variables

I. INTRODUCTION

As this century draws to a close. we humans are finally becoming aware of the effect our industrial cultural is having on the earth. Our continued use of natural resources in a nonsustainable and polluting manner is rapidly making our world less and less a fit place to live. Deforestation by the lumber industry: ozone layer depletion by the concrete industry: toxic byproducts of plastics manufacturing: squandering of fossil fuel deposits for manufacturing and transportation: all are actions which can be linked. in part, to our current cultural habit of a for profit based construction industry dependent on processed and manufactured products. An industry which finds its reason to exist thru promoting endless consumerism as means of enhancing the bottom line. This is a situation that has some serious problems for us all.

However, in adversity lies the seed of creativity.

What can be done to turn this situation around? one set of solutions can be found in the promotion and use of earth as a building material, Earth is a building material that is literally under our feet. It is everywhere, inexpensive, durable, and easy to use. Earthen construction has existed for millenia. Indigenous peoples world wide have developed locally intelligent methods of building with the earth. Earth has withstood the test of time as a means of fulfilling our common need for shelter. Earth as a building material and technique has many wonderful attributes. It only needs to be explored, used, and set free, In earthen construction can be found solution to some very serious problems.

Cob construction is one such way of BUILDING WITH THE EARTH.

II. WHAT IS COB

COB is a venerable earthen building technique which employs a mixture of EARTH, SAND, and STRAW, Cob has centuries old roots in England, and there exist today in Britain thousands Of ancient Cob buildings which nave been continuously occupied for hundreds of years. In addition, Cob structures nave been built since the middle 1800's in New Zealand as a result of European colonization, and have there shown Cob to be able to withstand seismically active geological conditions.

Currently in North America, Cob is experiencing renewed interest This is as a result of a series of workshops on Cob Construction which have been conducted over the past few years by the Cob Cottage Company of Cottage Grove, Oregon. In August of 1995 I attended a workshop they held in Point Reyes, California. During this workshop a group of 20 people came together for one week to construct a small Cob building. This was a seminal experience for me and I came away from the workshop with a desire to help bring Cob into our world of construction here in California. For me this has taken the form of introducing Cob into the Uniform Building Code.

III. WHY A COB CODE IS NEEDED

The Uniform Building Code (UBC) is a set of standards for the construction of buildings, and is used in most locations thruout the Western United States. These standards are developed by the International Conference of Building Officials (ICBO), published as the UBC, and adopted as law by most Local and County jurisdictions west of the Mississippi River.

The UBC covers most building methods commonly in current use. The list of included materials and methods does not include any Earthen Construction other than Adobe and this in only a very brief and limited manner. The UBC makes no mention at all of COB as a recognized means of building.

The UBC does allow for the use of "Alternate Materials and Methods of Construction". This is done on the basis of a by case" approval by the local building official. This results in the Alternate Material being judged for its construction suitability on the basis of what is written in the CURRENT UBC. An example of how this has been misused in actual practice is situation where RAMMED EARTH construction has been required to conform to Chapter 24 (masonry) of the UBC. Rammed Earth is not masonry, and to treat it as such is to do a disservice to both Rammed Earth and the UBC. Such a shoe horn approach, while understandable given that no appropriate earthen building standards exist, is faulted at best and could potentially be harmful.

What is needed is a REALISTIC CODE for each form of Earthen Construction, including: Adobe, Rammed Earth, Cob and any other method with which people desire to build. Anything less is not an optimum solution for building with earth in a SAFE, RESPONSIBLE, and REALISTIC MANNER.

IV. HOW TO CREATE A COB CODE

The key to making a COB CODE will be reliable data on how earthen materials will perform when used to create a building. There has been considerable scientific research done to date on Adobe, and some empirical knowledge has been gained from the case by case construction of Rammed Earth. However, Cob is quite different from both of these two more well known techniques, and there currently exists only empirical knowledge of how Cob performs as a building material. A systematic series of tests is called for to quantify Cob as a building material/technique.

Cob as a MATERIAL and a TECHNIQUE consists of the combination of a series of variables which when properly combined will result in a sound structure. Each of these variables needs to be identified and tested in a series of combined relationships with all the other variables. The GOALS of these tests also need to be identified. once the variables of: material, technique. and goal have been established it will be possible to design a TEST SERIES which will result in valid COB PERFORMANCE data. This data can then be used to develop a reliable Cob Code. The CODE DEVELOPMENT will also require identifying and establishing a set of goals about exactly what the Code is intended to do. This will all most likely not occur as a strictly sequential set of actions and will undoubtedly require including progressive feedback as the TESTING PROGRAM progresses.

V. GOALS OF A COB CODE

PRESCRIPTIVE CODE: a set of codified standards and methods which will describe now to build safely with Cob.

• How to analyze found earth
  • how to record and verify analysis results (for building inspector)

if funding allows, construct and test a series of two story 1/2 scale models similar to those used in the one story testing. if feasible, conduct tests both without and with bond beams. test models with: a bond beam only at the second floor wall top: and bond beams at both the second floor level and the second floor wall top. the total number of tests to be determined based on analysis of progressive results.

LONG RANGE TESTING

there is a body of empirical data that indicates problems with the use of PORTLAND CEMENT PLASTERS as finishes for earthen building materials. the UBC and some ADOBE CODES favor the use of this type of plaster as an exterior finish. the empirical data indicates that either exposed UNFINISHED COB or BREATHABLE LIME PLASTER is preferable. this is a serious issue that needs to be addressed. a series of long range EXPOSURE TESTS of wall panels with VARIOUS EXTERNAL FINISHES needs to be performed and evaluated for inclusion in future editions of the UBC. an interim solution to both exterior and interior finish standards needs to be discussed and proposed. such a testing program is not within the scope of this proposed COB STRUCTURAL TESTING PROGRAM.

Vlll LlST of Cob Construction Variables

• MATERIALS
  • found earth
    • percent of ingredients
      • organic matter
      • clay
      • silt
      • sand
      • rock
  • sand
    • particle size
    • particle shape
    • washed vs found
    • river vs lake vs beach
  • straw
    • species
    • growth period
    • length
  • water
    • potable
    • non potable
    • brackish
    • seawater
  • other organic materials
  • other additives or stabilizers
    • lime
      • hydrated
      • active
    • cement
    • asphalt
  • percent of ingredients in mixture
  • reinforcing
    • straw
    • steel rebar
    • other
• TECHNIQUE
  • establish % ingredients of found earth
    • jar test
    • sieve test
  • mixing methods
    • foot & hand
    • animal
    • rototiller
    • pug mill
    • mix to immediate use moisture content
    • mix wet & dry prior to use
  • aging of mixture
    • aging found earth with water
    • aging complete mixture
  • testing mixture samples
    • hand test to test sand content
    • brick test to test rupture strength
    • cylinder test to test compressive strength
  • application to structure
    • interpenetration of layers
    • application thickness
    • layer (course) thickness
    • drying time between courses
    • dryness of successive base courses
    • adding water to over dry base courses
    • surface texture of successive base courses
      • spine and rib
      • dimpled
      • holes
  • application method
    • pise
      • weight of trodder
      • foot area of trodder
    • cob loaves
    • gaab cob
  • air temperature
  • mix temperature
  • relative humidity
  • wind conditions
  • wall width
  • wall height
  • width to height ratio
  • form of wall
    • straight
    • curved
    • tapered
  • form of corners
    • square
    • angular
    • curved
  • wall penetrations
    • ratio of solid wall to openings
    • horizontal
    • vertical
    • lintels
    • arches

   

• foundation conditions
  • on grade
  • on rubble
  • on dry laid stone
  • on reinforced masonry
  • on non-reinforced masonry
  • key of wall to foundation
    • foundation top texture
    • foundation top keyway
    • foundation top projections
    • dowels out of foundation top
• wall bond beams
  • at intermediate floors
  • at wall top
  • concrete
  • wood
  • method of bond beam attachment to wall
    • texture
    • dowel
    • frequency and size of attachment method
• roof conditions
  • diaphragm
    • ratio
    • type and strength
    • attachment to walls
  • roof framing
    • rafters
      • sizes
      • load to wall
        • gravity
        • lateral
      • attachment to walls
  • roofing material
    • weight
    • durability / longevity
  • roof form
  • roof eave protection of walls
• wall finishes
  • interior
    • moisture permeability
      • liquid
      • vapor
  • exterior
    • moisture permiability
      • liquid
      • vapor
    • attachment to walls

• How to determine proper mixture
  • mix standards
  • imported material standards
• How to field test mixture / cob samples
  • required strength values that need to be met
  • required strength values for seismic zones
  • weight of wall sample
  • how to record and verify test results (for building inspector)
• Acceptable foundation methods
  • reinforced concrete
  • stone
  • CMU
  • other
  • requirements for seismic zone
• Foundation to wall key methods
• How to apply successive layers of cob
  • layer interpenetration standards
  • dryness limits between layers
    • how to correct for over drying
• Wall thickness to height ratios
  • for straight walls
  • for curved walls
  • allowable height / taper ratios
• Wall length standards
  • unsupported length / thickness ratio
  • lateral support methods
    • intersecting walls
      • cob
      • strawbale
      • masonry
      • frame
        • wood
        • steel
      • concrete
    • attachment methods
    • cob buttress
    • curved walls
• Wall openings
  • distance from end of wall
  • distance from corner in wall
  • length of wall between openings
  • opening size / unsupported wall length
  • lintel over opening
    • lintel size
    • lintel bearing
  • arch top opening
    • opening length / load above
    • opening length / wall height above
  • door / window attachments
    • operable
      • frame attachment requirements
    • inoperable
      • frameless fixed glazing methods
• Bond beam
  • when required / seismic zone
  • when required / wall openings
  • method of making bond beam
    • reinforced concrete
    • wood
    • attachment to wall
• Roof structure
  • rafter attachment
    • to wall
    • to bond beam
  • diaphragm boundry attachment
    • to wall
    • to bond beam
  • beam bearing in / on wall
    • allowable tributary area
    • bearing area required
• Floor structure
  • ground floor
    • wood
      • separate from walls
      • supported by walls
    • earthen
      • permeability
    • concrete
      • prevent ground moisture into wall
  • second floor
    • wood
      • supported by cob walls
      • supported by other structure
    • diaphragm connection to walls
• Placing other systems in wall
  • electrical
  • plumbing
  • mechanical
• Finishes
  • exterior
    • unfinished
    • breathable plasters
    • wood siding
    • roof eave projection required
  • interior
    • unfinished
    • breathable plasters
    • damp locations

  PERFORMANCE CODE: a set of design standards which will allow for Cob buildings which deviate from that described by the prescriptive code. To be used by licensed engineer or architect.

   

  VI. GOALS OF COB TESTING

  1. Measure material strength
     • compressive
     • rupture
     • shear
  2. Effect of mix material variables on strength
  3. Effect of mix technique variables on strength
  4. Effect of application variables on strength
  5. Effect of form variables on strength
  6. Ability of strength levels to withstand seismic loading
  7. Ability of form variables to withstand seismic loading
  8. Same for strength and form variables re wind loading
  9. Effect Of roof variables on strength and weathering
  10. Effect of wall finish variables on strength and weathering
  11. Effect of foundation variables on strength and weathering

   

  VII. A PROPOSED COB TESTING PROGRAM

  TESTS:

  ANALYSIS OF FOUND EARTH

  Using a series of found samples, perform seive tests to determine the exact percentage of sample constituents. attempt to find samples representative of typical native surface and subsurface soils ranging from 0% to 100% clay. Retest the same samples using various jar test methods. Develop a jar test method which will give results consistent with the actual percentage sieve tests. there are two goals to this testing:

  • develop a sample data base for further testing as described below
  • develop an easily performed jar test which yields accurate and reliable results

  MIX TESTS

  The objective of these tests will be to determine mixtures of found and imported materials that do not crack upon reaching a dry state. Perform a series of mix tests using: 10% variations of clay to aggregate (silt/sand/rock) add imported aggregate and clay as required. form into uniform 1-1/2" thick by 5-1/2" x 11" bricks and air dry. Note: limit found earth to aggregate ratio to those samples which are able to maintain sample cohesion when formed into a lump and dropped two feet onto a hard surface.

  perform the same series of tests on identical samples except with variation in imported sand (aggregate) particle size and shape. the number of test samples to be based on commonly available aggregates from both commercial and found sources. develop limits on aggregate size during testing if it becomes clear that sample cohesion or workability is negatively effected.

  alter test mixture procedure as necessary based on unanticipated results. add other constituents if needed to maintain cohesion and workability.

  perform the same series of tests on identical samples which contain straw. the amount of straw to be the maximum which can be mixed into the sample and still be hand molded into a cohesive ball.

  STRENGTH TESTS

  the first two strength tests are simple to perform and should be done with a number of samples based on the mixture tests. samples to be selected based on those that do not crack upon reaching dry state. total number of tests to be determined.

   

  1. COMPRESSION TEST

     test standard concrete cylinder sample. sample to be: height = 2 times diameter or, 2 high x 1 x 1 cubic sample test rate: 1mm/minute to failure

      

  2. RUPTURE TEST

     test wall section: l high x l wide x 3 long (between supports) load at center with two points 6" apart test rate: 1mm/minute to failure

  The third strength test will be more difficult to perform - it should be done using the strongest sample formula based on the first two strength tests. a main objective of this test is to quantify the reinforcing effect of the straw content. several tests should be performed using the following straw variables:

  • straw content by weight
  • straw species
  • average straw length

  the total number of tests to be determined based on analysis of progressive results.

  • 3. SHEAR TEST
    • test wall panel
    • 1 thick x 4 square wall panel
    • load panel diagonally from two opposite corners
    • load panel top vertically (simulated overbearing)

  ATTACHMENT TESTS

  the goal of these tests will be to test four common methods of attachment of other materials to cob walls. the total number of tests to be determined based on analysis of progressive results.

  • attachment methods to be tested
    • gringo blocks
    • porcupines
    • reinforcing bar dowels
    • bolts

  SEISMIC RESISTANCE TESTS

  these tests will require the use of a shake table and may also need extensive instrumentation. the goal is to determine how various structural shapes (consisting of walls only) will resist EARTHQUAKE FORCES (ground shaking and the resultant imposed inertial loads as will occur in an earthquake). other test goals are to establish limits for how wall thickness to height ratios can vary based on wall curvature. these tests should be based on the strongest wall panel samples resulting from the previous wall panel SHEAR TEST. the total number of tests to be determined based on analysis of progressive results.

   

  • SHAKE TABLE TEST
  • ONE STORY TESTING (walls only)
    • test 1/2 scale building model
    • first series of tests to be for walls without bond beams.
    • test three models
      • square with square corners
      • square with circular corners
      • circular or rectangular with square corners
      • regular oval
      • ellipse

         

      • base model dimensions on 8 wall height with a maximum unsupported wall length based on the results of rupture test. base on zone 4 seismic loading for scaled weight of model. test at varying intensities and durations until structure fails.

     

  • repeat the same series of seismic tests for those models that fail the first test series. this series to have a grade beam at the wall top.
    • test two grade beam types
      • wood
      • reinforced concrete

         

      • actual design of bond beams and connection to wall to be verified prior to testing. bond beam design based on required strength to resist calculated loads for zone 4 maximum predicted seismic event.
• ONE STORY TESTING (walls with roof diaphragm)

  conduct a series Of similar 1/2 scale model tests which include a wood roof structure which forms a horizontal diaphragm. diaphragm design based on required strength to resist calculated loads for zone 4 maximum predicted seismic event. the total number of tests to be determined based on analysis of progressive results.

   

• TWO STORY TESTING (walls, second floor and roof diaphragms)

  use data gathered with one story testing to calculate prediction of how a two story structure will perform

   

• if funding allows, construct and test a series of two story 1/2 scale models similar to those used in the one story testing. if feasible, conduct tests both without and with bond beams. test models with: a bond beam only at the second floor wall top: and bond beams at both the second floor level and the second floor wall top. the total number of tests to be determined based on analysis of progressive results.

  LONG RANGE TESTING

  there is a body of empirical data that indicates problems with the use of PORTLAND CEMENT PLASTERS as finishes for earthen building materials. the UBC and some ADOBE CODES favor the use of this type of plaster as an exterior finish. the empirical data indicates that either exposed UNFINISHED COB or BREATHABLE LIME PLASTER is preferable. this is a serious issue that needs to be addressed. a series of long range EXPOSURE TESTS of wall panels with VARIOUS EXTERNAL FINISHES needs to be performed and evaluated for inclusion in future editions of the UBC. an interim solution to both exterior and interior finish standards needs to be discussed and proposed. such a testing program is not within the scope of this proposed COB STRUCTURAL TESTING PROGRAM.

   

  Vlll LlST of Cob Construction Variables

• MATERIALS
  • found earth
    • percent of ingredients
      • organic matter
      • clay
      • silt
      • sand
      • rock
  • sand
    • particle size
    • particle shape
    • washed vs found
    • river vs lake vs beach
  • straw
    • species
    • growth period
    • length
  • water
    • potable
    • non potable
    • brackish
    • seawater
  • other organic materials
  • other additives or stabilizers
    • lime
      • hydrated
      • active
    • cement
    • asphalt
  • percent of ingredients in mixture
  • reinforcing
    • straw
    • steel rebar
    • other
• TECHNIQUE
  • establish % ingredients of found earth
    • jar test
    • sieve test
  • mixing methods
    • foot & hand
    • animal
    • rototiller
    • pug mill
    • mix to immediate use moisture content
    • mix wet & dry prior to use
  • aging of mixture
    • aging found earth with water
    • aging complete mixture
  • testing mixture samples
    • hand test to test sand content
    • brick test to test rupture strength
    • cylinder test to test compressive strength
  • application to structure
    • interpenetration of layers
    • application thickness
    • layer (course) thickness
    • drying time between courses
    • dryness of successive base courses
    • adding water to over dry base courses
    • surface texture of successive base courses
      • spine and rib
      • dimpled
      • holes
  • application method
    • pise
      • weight of trodder
      • foot area of trodder
    • cob loaves
    • gaab cob
  • air temperature
  • mix temperature
  • relative humidity
  • wind conditions
  • wall width
  • wall height
  • width to height ratio
  • form of wall
    • straight
    • curved
    • tapered
  • form of corners
    • square
    • angular
    • curved
  • wall penetrations
    • ratio of solid wall to openings
    • horizontal
    • vertical
    • lintels
    • arches

   

• foundation conditions
  • on grade
  • on rubble
  • on dry laid stone
  • on reinforced masonry
  • on non-reinforced masonry
  • key of wall to foundation
    • foundation top texture
    • foundation top keyway
    • foundation top projections
    • dowels out of foundation top
• wall bond beams
  • at intermediate floors
  • at wall top
  • concrete
  • wood
  • method of bond beam attachment to wall
    • texture
    • dowel
    • frequency and size of attachment method
• roof conditions
  • diaphragm
    • ratio
    • type and strength
    • attachment to walls
  • roof framing
    • rafters
      • sizes
      • load to wall
        • gravity
        • lateral
      • attachment to walls
  • roofing material
    • weight
    • durability / longevity
  • roof form
  • roof eave protection of walls
• wall finishes
  • interior
    • moisture permeability
      • liquid
      • vapor
  • exterior
    • moisture permiability
      • liquid
      • vapor
    • attachment to walls