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using cob infill on post and beam to eliminate need for knee braces?  RSS feed

 
michael Egan
Posts: 68
Location: central illinois
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I'm old to building but new to use of cob and wonder about how it bonds and works with wood. Could a post and beam structure be built with temporary angle braces and then infilled with cob to maintain stiffness and prevent racking? I'm skeptical about using these two materials together-- I live in Illinois which has lots of changes in temperature and moisture (rain, snow, high humidity, occasional droughts) and I think cob and wood react differently. Please let me know your experience. thank you
 
Topher Belknap
Posts: 205
Location: Midcoast Maine (zone 5b)
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Timer frames are engineered with the braces in mind. I have seen buildings where they were removed, which induced failures in the structure, not with cob admittedly. Generally braces work in tension (at least some of the time), I have little confidence in the tensile strength of a cob to wood joint.

Why would you want to remove the braces anyway, they make the frame beautiful.

Thank You Kindly,
Topher
 
allen lumley
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Location: Northern New York Zone4-5 the OUTER 'RONDACs percip 36''
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michael Egan : just as a suggestion -perhaps you could use your favorite search engine and type in timber frame cob homes images, Looking at the world wide
range of possibilities, give some consideration to the English Tudor House, there are many 700 years old For the good of the craft ! Big Al
 
Jay C. White Cloud
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Hi Michael E, et al,

First, let me give my welcome to Permies... as I haven't had the chance yet (I don't think...)

Michael Egan wrote:I'm old to building but new to use of cob and wonder about how it bonds and works with wood.


Very well for the most part, depending on formulation and tradition behind mix. Some "pull away" more than others, yet this is not an issue in many cases of "complete and thorough" builds in a traditional manner, as there is much more than just "throwing the daub (cobb) into the wattle."

Michael Egan wrote: Could a post and beam structure be built with temporary angle braces and then infilled with cob to maintain stiffness and prevent racking?


As a traditionally trained (and well seasoned Timberwright) the short answer is ABSOLUTELY...yet it all depends on the tradition(s) that are chosen to facilitate your timber frame.

Michael Egan wrote: I'm skeptical about using these two materials together-- I live in Illinois which has lots of changes in temperature and moisture (rain, snow, high humidity, occasional droughts) and I think cob and wood react differently. Please let me know your experience.


Well that is a "BIG" questions with many facets...

Some would (usually someone with little or no traditional timber framing background) say "don't do it" as it can't work. Well...it has...for thousands of years, yet most have forgotten how to do it well. One way to think of it Michael is ask yourself (I grew up in South Central Illinois and learn the craft from 14 years of age, till 23, from Old Order Amish) if there are log cabins in your area? (There are, because I have been the Historic Restoration Artisan on a few of them, including President Lincoln's cabin of his youth.) If these can work, a timber frame infill can work, and depending on the design, and the effort taken...it can work really well. If you really want to "upgrade," increase the wall mass thickness and design parameters by "mixing traditions" and modalities.

Topher Belknap wrote:Timber frames are engineered with the braces in mind.


Well...that is not quite the complete story...

"Bracing" is a funny thing with timber frames. "Oblique" forms (what is seen in Europe and those timber frame varieties brought here by Europeans) use the very stiff and rigid "oblique" styles that only work in compression loads, in almost all application...though some of those found in Switzerland of the Bernese Master Timberwrights, can work to a degree in both compression and tension, yet this is the exception not the rule as this is a very unique and ancient style,...probably some of the oldest in Europe. Oblique bracing also does add great stiffness to a frame (too stiff in some regards) and when they fail during a tectonic event they fail catastrophically in most caseses...

This is why the majority of timber frames, all 5000 plus years of them...and even most designed today globally and/or in areas with consistent and severe tectonic events (earthquake, tsunami) don't use "oblique" bracing modalities...they use "horizontal" systems...Like the Nuki 貫 beams, which are the fundamental bracing system in Japan one of the most tectonically active zones in the world (and with the oldest timber fame in the world at over 2000 years of age.)

With this system the frame achieves the necessary "stiffness" working in concert with the correct degree of "flexibility," thereby reaching a homeostasis between the two. Vermy much like the Asian Martial Arts.

Many "infill" methods incorporate the same principles as well.

Topher Belknap wrote:I have seen buildings where they were removed, which induced failures in the structure, not with cob admittedly. Generally braces work in tension (at least some of the time), I have little confidence in the tensile strength of a cob to wood joint.


If braces are removed from a frame that is designed to have them (like barns and old mills) there are issues that can occur, though this is often not as severe as some would think. The braces on many frames are there for the purpose of "raising the frame," and once this is complete the "infill and/or siding takes over the work, with the brace acting as a potential redundancy. This is not the case in all "oblique braced frames," yet most work this way that have this form of stiffing framework. It should also be noted that "oblique" bracing acts like a "fulcrum" in some designs actually weakening the converging joints in some locations.

I do have to state again that oblique bracing in most (almost all cases) DO NOT work in tension (like a strut which can work in both load paths) but in compression. This is why many frames (1/3 to 1/2 historically) that use this style of bracing do not even have any pegs in them, but rather wedges, as the "relish" in the tenon is not enough to withhold any "drawing force" of magnitude. The "wedged brace" system is still used even today, as it is a superior form to the pegged in many ways (subjective dependant on traditions followed.)

Why would you want to remove the braces anyway, they make the frame beautiful.


Agreed, to some they find these most pleasing...while to others...they seem to subject the structure to a "complexity of form" that detracts from the fenestration and overall flow of the structure...This point is strictly a personal one that must be chosen for its personal aesthetic.

Regards,

j
 
Topher Belknap
Posts: 205
Location: Midcoast Maine (zone 5b)
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I suggest that you make sure to get Mr. White Cloud's engineering stamp on all your plans. As he says:

Jay C. White Cloud wrote:...most have forgotten how to do it well.


Thinking you can resurrect a forgotten engineering craft, and then changing them by ""mixing traditions" and modalities." is a sure way to end up with your house in ruins.

There is a reason that certain building methods are "traditional", because if one doesn't follow the tradition precisely, one ends, badly.


Thank You Kindly,
Topher
 
Jay C. White Cloud
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Hello Topher, et al,

Sorry if my post was a bit to "directive" in nature, I was not trying to be rude in any way..., yet I feel compelled to provide more information to the other readers of this forum.

Topher Belknap wrote:I suggest that you make sure to get Mr. White Cloud's engineering stamp on all your plans.


Ummh...I don't believe I wrote here (or in any other post??) that I was a PE of any type...

I have said many times on this forum...and thank you for bringing it up here once more...that any uncertainty of a design should be reviewed not only by a PE, but also by a professional in the given architectural design modality a reader may choose. I have also shared before that I do work with, on our team of traditional Artisan, a wonderful PE that is also a founding member of the Timber Framers Guild. So I will stress here once more, that being well versed in the craft and the engineering is paramount in all substantial and enduring designs.

Topher Belknap wrote:Thinking you can resurrect a forgotten engineering craft, and then changing them by ""mixing traditions" and modalities." is a sure way to end up with your house in ruins..There is a reason that certain building methods are "traditional", because if one doesn't follow the tradition precisely, one ends, badly


I agree...anyone that believes they can (on their own) "resurrect" a form of architecture...especially many of the traditional and/or natural styles...they very well may experience some form of "ruin," ...either major or minor. This is not to say, that these traditions have not been preserved, and that there are not those among us that have made it a life times pursuit in learning them, and associating themselves with others that have. I have been blessed to learn many of these traditions from unbroken lineages of "knowledge holders," like the Amish, and now get to collaborate with many more (thanks to technology and travel) like those in Japan that have been Daiku 大工 in the same family for over 1000 years. This type of lineage, knowledge, and experience can not be found in books, or in the formulas and "comparative statistical charts" of the Engineers.

With the correct orientation (and trained experience) one CAN successfully mix different modalities, that complement each other and use similar natural materials in similar ways. As I am known for writing here, and stressing to our readers...look to the vernacular, when considering a "Permie Build." These traditional forms whether "pure" or "accumulative" in nature, can yield a secure, effective and efficient structures that will last for centuries, as their predecessors have demonstrated.

If the failure of a timber frame (or some other traditional/natural architecture) is a personal experience, I am sorry that it happened. I too become very frustrated (more so in the last decade) with many current building trends that "unknowingly" facilitate poor guidance. This ranges from "workshops" where the facilitators have little or no background in the given architectural form...to conversations on forums like this one, as it can be very difficult to tell if the information is accurate and/or valid. This is why I stress to readers to scrutinize information well, ask questions, and if taking a workshop, following advice, or seeking guidance...PLEASE DO...examine closely all information gathered...especially on the internet!

Respectfully,

j
 
michael Egan
Posts: 68
Location: central illinois
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My thanks to your comments and advice. I think all of us who endeavor to build with more natural materials encounter issues that challenge our plans and eventually, our structure. Your thoughts are helping me to ponder more before building in hopes of experiencing fewer failures and "do-overs" after I start. Keep talking.

Michael
 
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