Log truss info

Having spent a few years working with wood in the round creating mainly A frames and post and beam. I would like to explore creating more open spaces like community builds,workshops and such which has brought me to thinking on roundwood trusses to create open spaces. Being in the uk it seems there is limited information on roundwood trusses. Ive read a bit on the internet to know that its not straight forward and a risk from failure if not done properly. I believe it can be done without metal fastenings which is my ideal way to. Just relying on the joints and pegs.Species of wood used in the uk would be an advantage as again its limited information. Look forward to this discussion.

Hi Dylan,

I am not sure if you have seen the "book list" I have provided here at Permies, but you may find some of the referenced tombs of worth. I can think of a number of "truss designs" from timber framing that would (could?) be of value. Let me know what direction you are thinking, as the simple "King" or "Queen" post truss system would probably be a good start.

Regards,

j

It certainly can be done. Carpenters in medieval England built amazing structures, some of which still stand, with little to no metal involved.
I have a book, Historic English Carpentry, which gives details of joints and overall layouts of buildings, among other things.

Thanks for the reply's. After i posted i see there was a similar thread posted recently with the "wish list" So many books but will short list.
I like the king/queen post frame of a truss and would like to explore how the forces work on this particular truss.As i understand it the rafters are tennoned into the tie beam, How do you determine the shear plane beyond the tie and distance? The rafters towards the ridge are again tennoned into the king post, same question there.
Ive just finished with a team of guys a traditional West Sussex oak framed barn.

https://www.facebook.com/media/set/?set=a.369273303211776.1073741852.262540133885094&type=3

On framing up the roof we tennoned the principle rafters into the tie beam but only used a bridle joint above, fine for oak but a bit more challenging in the round?
Which brings the frame round to using a king post and more appropriate.I see from your previous thread that one book doesn't reveal all on framing up trusses.So gathering information and span tables/spread sheets am finding hard to achieve, maybe there's a book in there for someone!.

Thank you and look forward to exploring the roundwood truss some more....

I do log and timber work but I'm in pine and spruce country although I have used a fare bit of oak for framing. Allan B Mackie is one of my favorites. I know this is a different style but his books have lots of round wood truss advice and info about scribers you will need to master when doing round work.

Hi Dylan,

With that kind of experience behind you, there should be not too many challenges for achieving a truss in "live edge" timber....Looks like you had fun...

Dylan Walker wrote:I like the king/queen post frame of a truss and would like to explore how the forces work on this particular truss.

These are the two most common foundational forms found in "western" styles of timbered truss work. Both are strong, elegant and capable of considerable clearspans. The next most popular is "hammer beam" systems. The question to often ask ourselves, as designers, when facilitating "domestic" and not "commercial" space..."do we actually need a "clearspan?" Often the effort is not warranted because of the need for internal partitioning. We often see the novice designer, for example, place the hard work of a "hammer beam" bent in a gable wall...??...which is both illogical and too often a waste of effort, as this is an external diaphragm to the frame and does not benefit either structurally or aesthetically from this type of truss...

Dylan Walker wrote:As i understand it the rafters are tenoned into the tie beam, How do you determine the shear plane beyond the tie and distance? The rafters towards the ridge are again tennoned into the king post, same question there.

The rafters or more specifically in this design modality, the "principle rafters" are indeed "tenoned and seated into both the "tie beam and upright timbers (i.e. queens and/or kings.) These are critical bearing joints that make the entire system work in concert as a truss. Not all have a "ridge beams" yet probably should for both structural reasoning and ease of other building efforts of the frame.

As for shear loading, in accordance with..."shear plane beyond the tie and distance," this will be dependant on actual truss system type, joint types selected, specific loads parameters, wood species, size and actual span. If speaking of just the "shear plan" of the "principal rafter seat" that again is beholding to the species, joint design and other parameters. This is a reason I never privately or publicly suggest "truss work" done by a novice Timberwright, that is not checked by a well seasoned PE with specific "traditional timber framing" experience. Many of these DIY trusses have failed, from lack of "back checks" and extensive knowledge required to "self engineer" them. I state this as "information to know," not to dissuade, as you should still pursue the task, but understand fully the risks and knowledge base require to be "safely" successful.

We still often "hind" hidden metal elements just to give extra insurance for the unforeseen loads these frames may see over the possible "centuries" they may have to work within a structure. Studying the historic examples demonstrate the "fail points" of such trusses and give us the advantage of understanding where they can become compromised over time.

Dylan Walker wrote:On framing up the roof we tenoned the principle (principal?) rafters into the tie beam but only used a bridle joint above, fine for oak but a bit more challenging in the round?

The challenge is the "live edge" from a layout perspective...which is considerable...but does not affect strength of the final truss if designed, engineered and jointed properly, and well. "Live edge" timber work is always inherently stronger (often by some great margins) than that of "canted work."

Dylan Walker wrote:Which brings the frame round to using a king post and more appropriate.I see from your previous thread that one book doesn't reveal all on framing up trusses.So gathering information and span tables/spread sheets am finding hard to achieve, maybe there's a book in there for someone!.

The info is almost all there (field work with Master Timberwrights is invaluable in this advanced framing modalities) yet the information is not in one specific book...

I look forward to following along...

Regards,

j

Many thanks for taking the time to reply to my info on Roundwood trusses.I really appreciate that there is many factors to resolve before even contemplating a truss layout let alone find a structual engineer who can work with you sensible.
Would looking at heavy timber framing be a good starting point or is trusses in the round stand alone framing?
My feelings are
That species of wood would be questionable in the UK?Not a lot of testing in the round here.
Finding a structual engineer who understands.
Find an appropriate course,timber wright.
Thanks for letting me bounce this around.i know the answers will come

Hi Dylan...

Dylan Walker wrote:Would looking at heavy timber framing be a good starting point or is trusses in the round stand alone framing?

Absolutely! Please do look at general timber frame truss design (and trusses in general as the load paths are the same.) I will let you in on a "little secret," most PE work done for log architecture just employs the statistics for regular canted timbers. "Live edge" framing, thereby is usually considerably stronger than cant timber frame work.

Dylan Walker wrote:My feelings are that species of wood would be questionable in the UK?Not a lot of testing in the round here.

It is a given that the selection of timber species is more limited in the U.K. than here in North America or perhaps even Europe at large. This does render a wee bit more of a challenge, yet not overly so, especially because you are working in the "live edge." Live edge timbers are often way more common than "straight." These can be secured from local Arborists, and even from "forest thinning" projects, as often these members are discarded into "junk wood" for mulch heaps, or fire wood. They "appear" to be of lower quality, yet often are not...just crooked, very much like the "Cruck frames" the U.K. and Europe is known for which is a rudimentary truss.

Dylan Walker wrote:Finding a structural engineer who understands.

They are there and when the time is at hand we will find you one. The TFG here in the states has quite a few U.K. members that can assist in this challenge...should it actually become one.

Regards,

j

That's great news, thanks ever so much.Rule of thumb we have been looking at the square within the round for sizing already. I hear that it's as half as strong,happy days.I would love to work with sweet chestnut due to its architectural look for truss work but I caution the thrusts at the ends due to its cleaving capabilities.Balancing beauty with capabilities can be a fine line.
Are bases of framing with live edge is square rule with scribing,lapped over.I have a good understanding but know hunger for more!
I have a couple of personal projects all being well with permitted development to create an area 7mtrs clear span wide by 10 Mtrs long using trusses.Thats the goal. What do you reckon?