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Author Topic: Glossary of Terms (printed version)  (Read 3233 times)

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Offline Jim_Rogers

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Glossary of Terms (printed version)
« on: August 11, 2003, 07:12:07 AM »
There is a magazine available from the Timber Framers Guild online store called Timber Framing, Journal of the Timber Framers Guild. The June 2003 issue number 68 has an article on page 12 titled "Timber Framing for Beginners" VI, A Glossary of Terms. It is six pages long. It contains 294 terms and their definitions.
If someone is interested in Timber framing this magazine would be a good one to get to start to understand the terms of timber framing.
It was collected by the Exe. Director of the guild and the Editor of the magazine from quite a few books, with more terms added by specialists in each field of timber framing, such as steeple building, bridge building, engineering, and historic American timber joinery.
The cost of this 'back issue' magazine is $5, and you will be able shortly to order it online.
If you are truly interested in Timber Framing you should join the guild for $75 a year and you'll get this magazine as well as a monthly newsletter as part of your membership. You can gain a lot of information about timber framing from these publications.
Jim



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Offline smwwoody

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Re: Glossary of Terms (printed version)
« Reply #1 on: August 13, 2003, 09:03:22 AM »
Thanks for the try jim .

You might want to try posting them full size to a web site like the free space all of us have here then put a link to them in the post
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Offline Jim_Rogers

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Re: Glossary of Terms (printed version)
« Reply #2 on: August 14, 2003, 06:14:13 AM »
smwwoody:
Can you point me to the page or link of how to do this? I'd be willing to do it if they can be read by the average computer user.
I'm not familiar with the procedures to upload to the free space you've mentioned.
Thanks,
Jim
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Offline smwwoody

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Re: Glossary of Terms (printed version)
« Reply #3 on: August 14, 2003, 08:13:24 AM »
Jim

I'm not real sure how to do it eather but I know it can be done.  I'm  sure someone in the know will see this and lend thier help

Woody
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Offline Jeff

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Re: Glossary of Terms (printed version)
« Reply #4 on: August 15, 2003, 03:29:46 PM »
I sent jim a PM to see what we could do.
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Offline smwwoody

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Re: Glossary of Terms (printed version)
« Reply #5 on: August 15, 2003, 07:05:42 PM »
Thanks Dad :D
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Offline Jeff

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Re: Glossary of Terms (printed version)
« Reply #6 on: August 19, 2003, 07:22:32 PM »
That O.K. my boy. Now clean yer DanG room.

Waiting for the info from Jim.
Just call me the midget doctor.
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Offline smwwoody

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Re: Glossary of Terms (printed version)
« Reply #7 on: August 19, 2003, 08:59:30 PM »
I,ll have you know that I was puting tools away in the dark tonight just so I could keep it clean.

No power in the tool shed yet  :(
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Offline ponderosae

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Re: Glossary of Terms (printed version)
« Reply #8 on: September 20, 2019, 07:11:22 AM »
Thanks. I hadn't seen the term "collar purlin", for one. There was something odd about it though, when I looked for pictures of those(?)... well, firstly a couple of other definitions led me to picture it as a set of purlins, however no photographs of that seem to exist (just one diagram from a slide, below). Actual pictures instead indicate that a "collar purlin roof" is synonymous with a "crown post roof", in which there is one purlin under the center of several collar beams, whereas a "clasped purlin roof" shows two purlins, although they are on top of the collar beams.  I wonder if those two terms got mixed up in the following definitions (or perhaps it isn't as common as the one purlin there):

Collar Purlin Roof :


Quote
In this type, long beams called purlins run the length of the roof, tying the rafters together. Both a collar and a tie beam are placed across the width of the building, and various braces may be added to give extra strength.

Houses and Cottages of Britain :


Quote
In the crown-post-and-collar-purlin roof each pair of rafters is joined by a collar (1), the collar purlin (2) runs underneath the row of collars, the crown-post (3) rises from the tie-beam to support the collar purlin, and is braced to collar and collar purlin and sometimes to tie-beam also.

Re-reading the second definition above, it seems to describe one purlin (okay then, maybe the '(2)' threw me, or I had a preconceived notion of two purlins everywhere). A church glossary also shows the same picture for either the collar purlin or the crown post roof, with only one central purlin. So there seems to be a consensus, except for the first definition above, where a diagram is shown in the book with two purlins (slide 25 there). It also distinguishes between a crown post roof, with a "crown plate", instead of calling that a "collar purlin"... yet, as I said, there don't seem to be any historical photos of a roof with two collar purlins, like the way it's shown in their sketch.

Offline Jim_Rogers

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Re: Glossary of Terms (printed version)
« Reply #9 on: September 20, 2019, 10:46:50 AM »
There are many names for the same timber depending on the location of the frame. Whether it is here in the USA or overseas. And there can be local difference in the names depending on who is labeling them.
The writers of these books are giving them the names that they know from their research of their area.
And they can vary with our names of what we would call an American frame.

It is difficult to get the exact name right in all locations due to these differences.

Jim Rogers
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Offline ponderosae

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Re: Glossary of Terms (printed version)
« Reply #10 on: September 20, 2019, 04:35:11 PM »
Oh yeah, there's not even much info on the word purlin by itself.


Quote
Information on the origin of the term is scant at best. According to Websters it comes from 15th-century English. According to the Oxford Concise Dictionary, it is "Middle English, perhaps of French origin". Other sources reference Middle English or 15th-century English.

Offline ponderosae

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Re: Glossary of Terms (printed version)
« Reply #11 on: September 20, 2019, 04:56:21 PM »
The discrepancy with names wasn't really what I found odd about it though. I'd think that two purlins would work better with one on either side under the collar beams than one purlin in the middle of them, so it's strange to me that the only pictures representative of a collar purlin roof in actual use show the middle crown plate design.

Offline btulloh

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Re: Glossary of Terms (printed version)
« Reply #12 on: September 20, 2019, 05:09:27 PM »
Perhaps you should publish a book on timber framing that corrects all the design errors that have been perpetuated over the ages. 
HM126

Offline ponderosae

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Re: Glossary of Terms (printed version)
« Reply #13 on: September 20, 2019, 08:18:55 PM »
Alrighty, I'm done talkin with you guys if yer gonna fall off topic like that: TIMBERRRRRRRRRRRRRRRRR...........

Er make that HOLLLLZKLOTZ (wooood log)... oddly funny, yeah I had to look at a German glossary to find an example of that kind of 'dach-stuhl' (roof-timbering or roof-truss), which is an upright-, stehender-Stuhl: "Unlike a purlin, a collar plate never carries the rafter directly, but only indirectly via the collar beam." So these framing pieces are called 'rahm' or 'stuhlrahm', as collar plates (instead of a collar purlin or crown plate), when used in tandem (or mittelpfetten I should say), and are commonly found as the double frame of a chapel (kapelle). One of the oldest examples is a 9th century one called Einhardsbasilika, which had this roof added in 1541. Then from 1900, there's a model of the dachstuhl, which indicates that it was mostly used in smaller buildings since then (as it is explained in a Dutch book that the angled-, leigender-stuhl was preferred in larger buildings). However, I hadn't found an example of the smaller stehender stuhl in current usage, as it seems that the terminology has been changed in such instances (like the dachstuhl here), referring to pfetten (purlins), running longitudinally (langsrichtung) under the kehlbalken (collar beams), or 'kehlbalkenunterzug' in one word. Whereas a set of pfetten, without the kehlbalken connecting them to the sparren (rafters), would be called a pfettendach (or dachpfetten), in addition to a sparrendach, or what ever else they want to call it (like another kind of dachstuhl).

Well now we're on topic, in another language, so I'll just call it eclectic.

Offline ponderosae

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Re: Glossary of Terms (printed version)
« Reply #14 on: October 14, 2019, 07:51:21 AM »
Otherwise, I was reading about how collar ties are actually in compression, for roofs with a slope of 4 in 12 or greater (even though a 'tie' typically refers to a beam in tension). They say a collar tie can perform the same task as a purlin, except that it uses the opposing rafter to prevent sagging. Now I see what the purpose was of a crown plate under the middle of the collar beam spans—in case those deflected in compression, since the collar beam is actually substituting for purlins on either side. I just had the general impression that all tie beams were in tension, and the references I found about collar purlins didn't seem to explain as much, so it was a wonder what the point of that was.

Except in comparison to a king post, which holds up a tie beam in tension (because it can sag this way too, particularly under its own weight for having a longer span at the bottom of a truss), but that's a different set up (with the post on top of it), and if the collar ties were similarly in tension, they could have simply used king posts on top of those.

Likewise, the comparison between a collar purlin (or crown plate) and collar plates (underpurlins) is one of a difference between the collar beam either taking the place of purlins (besides one underneath it for reinforcement in this case), or a collar being there to connect the purlins to rafters (on either side of it). Functionally, they would be similar though, in order to take on compression from the rafters.

However, there must be a fine line between tension and compression in tie beams, since the article about collar ties in Canadian construction says they are placed at the mid-span of rafters to be in compression, while rafter ties are placed in the lower third of the span to be in tension. I guess collar ties may work either way, especially when placed in the upper third, since they are said to help hold the ridge of the roof together as well. Not only are the names sometimes interchangeable, it's about what the framing does interchangeably also.

Hopefully not fall apart like this discussion (the framing that is)! Can I buy a Vokal?

Offline Jim_Rogers

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Re: Glossary of Terms (printed version)
« Reply #15 on: October 14, 2019, 05:10:00 PM »
there must be a fine line between tension and compression in tie beams, since the article about collar ties in Canadian construction says they are placed at the mid-span of rafters to be in compression, while rafter ties are placed in the lower third of the span to be in tension. I guess collar ties may work either way, especially when placed in the upper third, since they are said to help hold the ridge of the roof together as well. Not only are the names sometimes interchangeable, it's about what the framing does interchangeably also.
 

The engineers at the Timber Framers Engineering Council have done structural analysis of "collars" and they are in compression when they are above 1' of the plate. At 1' or below they are in tension. Holding the plates from spreading.

One well known timber framer suggested that the name "collar tie" be used only when the collar is 1' or lower to the bottom of the rafter, as mentioned that is the only location that it is truly "tying" the timbers together. Any other location the collar is in compression. After reading this, and understanding that every timber, in a frame, gets its name from its location, I have been calling any collar above 1' a "collar beam"
Others should adopt this new name and definition, but that most likely will never happen.

Jim Rogers
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Offline Don P

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Re: Glossary of Terms (printed version)
« Reply #16 on: October 14, 2019, 07:41:17 PM »
If there is not a supporting ridgebeam or something else supporting the rafters, any single tie across the rafters, no matter how high, is in tension. Mock up model roof using a greeting card sitting tent fashion on a smooth table. Use a needle and thread to create a tie. First place the tie at plate elevation, the table level. Push down on the ridge. The rafter feet are tied and do not spread. The rafters can bow. Put a collar beam, say a toothpick taped into place up somewhere around midspan, push down on the ridge and that compression member will help brace the rafters, but only in conjunction with something restraining the thrust. Just as you see in the Canadian roof in the home inspectors report, two levels of ties. Cut the thread removing the lower tension tie and push again, the toothpick, now a single tie, in tension, falls free as the rafter feet slide apart.

Back to just the thread again, make a tie at midheight or higher, push down. The feet slide outward, the rafters bow mightily, the tie tries to restrain the thrust, it is in tension however it also puts a lot of bending stress on the rafter. As that attempted raised tie moves higher in the roof the stress on the rafter and tie connections increases. The high posted cape example in the red book shows this as well.

Look at the rafter span tables in the codebook, https://codes.iccsafe.org/content/VRC2012/chapter-8-roof-ceiling-construction
scroll down to table 802.5.1(1-8), read the footnote at the base of each table, there is a correction factor to be applied to allowable span as the tie is raised. When the tie, in tension, is raised 1/3 of rafter height the allowable span is decreased by 1/3 due to that bending force from the tie. Scroll to the last table (9) the heeljoint/tie connection table, again scroll to the bottom and you will see a need to beef up the connection strength as the tie is raised above the plate.

In a simple rafter triangle the only time a collar tie can be in compression is if there is a rafter tie below it taking care of the tension. Usually :)

In stick frame construction that upper collar tie, in the upper third of roof height, or a strap over the ridge connecting the rafter couple and ridge together, is intended to be a tension element in the event of uplift. The physics are not different.
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Offline ponderosae

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Re: Glossary of Terms (printed version)
« Reply #17 on: October 14, 2019, 11:28:05 PM »
Ah, so between what each of you are saying there, I was re-reading something about the Basic Design Issues in Timber Frame Engineering, because I kind of skimmed it at first (in order to answer some other questions about purlins). They also explain how a raised tie is under greater tension, unless it is above an existing tie at the plate (or maybe a tie below plate too). Their example is a king post truss, which handles the tension at the plate better than a tie beam alone in longer spans, and then adding a 'collar strut' above it handled compression in the rafters, which formed a Roman Truss (or alternately the diagonal struts added to a king post act as a collar beam in compression). As y'all said, tie beams can work both ways much better if they are used together at different levels to handle tension below and compression above (like the crown post roofs, or dachstuhls too, which would additionally reduce tension at the plates).



Speaking of which, I was looking at the picture of a frickin sparren-pfetten-dach-stuhl again (which uses three levels of purlins or pfettens, instead of collar beams and rafter ties with purlins in between, like the stehender-stuhl); it also has king posts going between the purlins. So what's up with that... are the king post trusses in tension or compression there? I would guess both, potentially (compression from the rafters and/or the ridge purlin, and tension from tying the middle purlins together). More likely tension though, most of the time, since it all seems redundant enough otherwise. I gather this is like moving the top plates up to the mid-purlins, in essence, and the lower half behaves like a simply supported shed roof on either side (with no thrust or tension there, since it doesn't have any ties at the bottom). In other words, that timber engineering reference says a ridge beam divides a roof in half to eliminate thrust (like a shed that is only sloped on one side), but with a longer rafter span like this, the mid-purlins seem to have trusses between them in order to neutralize the thrust at mid-span (with tension there), and divide it into separate shed halves underneath, which have only down force on them. So in this case, the roof framing is handling tension above and compression below.

Offline Don P

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Re: Glossary of Terms (printed version)
« Reply #18 on: October 15, 2019, 07:41:23 AM »
It appears to be designed as a kingpost truss supporting a ridgebeam, notice the joinery of the truss is capable of supporting the head of the kingpost and directing load down to the heels of those top chords. The kingpost, or kingrod, appears to be clear of the tie. This is glulam and has nice appearance. I notice they used bolsters on the posts and have an off post simple lap scarf in the plate that I'd bet has a threaded rod or bolt through it.
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Offline ponderosae

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Re: Glossary of Terms (printed version)
« Reply #19 on: October 15, 2019, 10:56:01 AM »
Yeah that's a long beam span (they call it the firstpfette, and the glulam is Brettschichtholz). It seems like the truss is set up there for support in each direction then.

I was just looking at another image of a carport that shows the 'querpfetten' (cross purlins) of a simply supported shed too (it's kind of like looking at one side of that pfettendach, without the firstpfette).


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