[GSBN] Catalan vaults

Tue Dec 13 02:49:12 UTC 2011

Derek and all, 

As the one who set this thread in motion, I was also getting a bit concerned that the discussion, while labeled " Catalan vaults " was wandering into all manner of other vaulting techniques such as thin shell concrete, brick bovedas, compressed earth blocks, etc. that differ greatly from what I was raving about. 

So to clarify:  a major, perhaps THE major distinction of Catalan vaulting from other traditional masonry arch techniques is that you have several layers of terra-cotta ( or recently,  machine-pressed soil cement ) tiles  bound together,  and the joints between individual pieces,  being offset between layers, do not run straight through the thickness. This gives the structure a great deal more inherent cohesion than blocks of stuff locked in place by gravity. 

If anyone is advocating THIS approach with unfired,  unstabilized earth,  they are smoking the wrong stuff. 

 There are a number of other benefits of this " plywood " approach, including that the use of small thin units, normally a drawback in traditional vaulting,  makes the creation of double curvature much easier, which greatly increases the stiffness of the structure. And you don't have to shape complex,  three dimensional pieces to get them to lock together. 

The Guastavino Company was building these things all over the U.S. in the first part of the last century, and the subsequent track record of the buildings has been excellent.   

As to the high stresses in low arches:  there is obviously a need to match the rise to the conditions.  For long spans the domes were normally at or close to spherical profiles, partially because this was the Beaux Arts style ( i.e.,  ape the Romans ). When they were supporting floors (  on much shorter spans )  they would make the vaulting much flatter. And would include vertical ribs,  creating an egg crate, to stiffen them from the back. Nowadays we can make the profiles caternary without much trouble. 

As to the concern about getting the geometry exactly right: if you look closely at some of the interior shots of the South African project I linked to, the very white mortar lines show that there are several places,  in quite large spans,  where the vaults bent a little, implying that it is not as demanding as you're imagining. 

I can only speak from book knowledge ( so far ),  but it  seems to me the equivalent of bale construction for walls. There,  you have to get the moisture issues right. Here, you have to get the structure right. But it's within the skill realm of a tradesman, not a rocket scientist. 

And since we will be insisting on enough roof thickness to accommodate a great deal of insulation, it's  not likely to end up a thin-shell structure like we architects have been so enamored with in Modernism. Insulating it is the part that really needs work. 

Basic observation: we really, really  like arches and domes. If there is a "structophilia", they are way up at the top. My entirely intuitive sense is that we don't trust heavy looking stuff that's flat overhead. We intuitively know it's in a lot of tension,  and we trust compression more.  Even wood beams feel better when they're bowed. 

But we keep roofing our all-natural  buildings with tension-capable "sticks" of various kinds, which the pull of convenience keeps forming into flat ceilings and flat openings   It's worth keeping this in mind.  

Bob

On Dec 12, 2011, at 3:31 PM, Derek Roff wrote:

> It's great to see what people are doing with thin, low-arch vaults and domes.  Obviously things are working for them.  However, I am concerned about safety.  With every building material and design, as we push toward the extremes, the risk of failure increases.  And when failures occur, they are more likely to be catastrophic.  Traditional building forms, methods, and materials tend to have a lot of redundancy, and are usually quite fault tolerant.  More modern, optimized, resource minimizing designs and structures require everything to be done right, and run the risk of collapse from the failure of one or a few key elements.  
> 
> I feel concern about the Catalan arches in this regard.  Individual pieces of the arch are each in high stress.  The perimeter of the low-arch shell experiences forces many times the weight of the dome.  Small horizontal displacements can lead to structural failure and collapse across some or all of the dome.  Few of us have trained our intuitions sufficiently to make accurate judgements about many of the design and building details.  
> 
> I'm not suggesting that no one should experiment with these structures,  Rather, I am calling for us to take proportionately greater care and to pay substantially greater attention to design, materials, and construction details, when the risks are higher and harder to judge.  I wonder if Bruce, or other engineers on the list, would comment on building Catalan domes with unfired earthen materials.  
> 
> Trying to keep our heads in the clouds, and out from under the bricks,
> 
> Derelict
> 
> Derek Roff
> derek at unm.edu
> 
> 
> On Dec 12, 2011, at 12:02 PM, huffnpuff at q.com wrote:
> 
>> Chris and All,
>> 
>> I do remember perusing the info posted for the Catalan vaults and found it most interesting. About a year ago I had an opportunity to attend a charrette on Compressed Earth Blocks, hosted by Bernard Amadei at the U. of Colorado. These CEB builders were meeting to discuss similar issues that we SB builder types are/have experienced with acceptance, testing, codes etc. Two fellows of particular vision and spirit were Satprem Maini from the Auroville Institute, India http://www.earth-auroville.com/vaulted_structures_introduction_en.php and Jim Hallock, of icatis, USA http://www.icatis.org/, both NGO's building with CEB's and Vaults/domes. Both web sites are full of the work these two organizations have done and are eye candy for anyone interested in vaults. If you visit the icatis site you'll see they have teamed with George Nez and built at least one of his 'thin shelled latex concrete' roof systems.
>> 
>> Currently our local engineer and COSBA member Ian Smith and his wife (both engineers) are on their honeymoon in India at the Auroville Institute at a workshop on vaults. That's devotion...
>> 
>> Mark Schueneman
>> COSBA 
>> 
>> 
>> ----- Original Message -----
>> From: "Chris Magwood" <chris at chrismagwood.ca>
>> To: "with public archives) Global Straw Building Network (private" <GSBN at greenbuilder.com>
>> Sent: Sunday, December 11, 2011 9:55:05 AM
>> Subject: [GSBN] Catalan vaults
>> 
>> Hi all,
>> 
>> The mention on this list some months back about Catalan vaults (or 
>> Guastavino vaults) sparked my interest, and we've now decided to forge 
>> ahead and build one as the roof for a buried, earthbag root cellar at 
>> Trent University.
>> 
>> Does anybody have experience building these, or know of anybody who 
>> does. I'd like to try and hire in somebody to lead us in this build. 
>> It's a small structure (18 x 22 ft) so it won't be a long build, but I 
>> always like to have someone knowledgeable in charge when doing things I 
>> haven't done before.
>> 
>> The budget for the project is not high, but I would be willing to try 
>> and cover travel costs, food, lodging and a bit of cash for the right 
>> person.
>> 
>> Let me know!
>> 
>> Chris
>> 
>> -- 
>> www.chrismagwood.ca
>> www.endeavourcentre.org
> 
> 
> 
> 
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