Hi,

Recent mention has been made about the efficacy of some timbers in service (Brungraber) and the multitude of tieing joints types (Sobon / Lewandoski) that can and are employed in timber-framed buildings.



I thought that I would share some of the hard realities of life (and death) of a timber-framed building with the timber-framing community.

The English tieing joint assembly has been employed thousands of time but eventually (some considerable time ago) this joint or more correctly the structure yielded causing the tieing joint assembly to move apart. The post top rotated outwards breaking the teazle tenon and breaking the cross brace pegs. In very simple terms A + B = C where the outer edge of the wall plate is not completely clear and the possibility exists that the wall plate has been replaced at some point since the shoulder of the lap dovetail seat is not completely evident.

An attempt has been made at some time in the past to strap this joint together using an old metal cart tyre which is the most frequently encountered method employed to strengthen this type of joint. It works. With the passage of time these straps have also become an architectural feature worthy of preservation.

I sometimes wonder if the complex detail calculations and analysis undertaken by north american timber-frame designers on timber frame joints are really worthwhile especially when an old cart tyre is a solution that can deal with a multitude of woes.

This building has now been standing for 689 years !

P.E.'s and anyone else please discuss

Ken Hume

You must take into consideration the electrical wiring in the equation.

Does this building have common rafters? or is it pure purlins? Where does the thrust come from to effect such damage to this joint, and then construct in a manor that avoid these forces.

Any evidence of using cogs in stead of the dovetail over there?

Hi Tim,

The cables - yes - now there's a glimpse of the obvious !

The building is as shown below :-



and has a crown post roof with common rafters and hence no side purlins. The location of the blown tieing joint is as indicated in the sketch. This is a tall slim town building with an end jetty and a very large open 2 bay upper room at the front.

Cogged tieing joints are employed in English timber-framed buildings but as yet there is no real significant statistical evidence of where and when these can be found.

Ken Hume

Hey Ken, et al.,

Ben, Jan and Jack, are all "Nuts," and I love them for it, but Ben is really the "character" in the group, and actually he and the team he works with is our "go to" PE, and have been for decades. It would be great if they added their voice to this conversation.

The "English" tying joint and its related species in other wood cultures of perimeter "3 way connections," can be very efficient and strong, but also in some forms very susceptible to failures (especially if modified.) Yet “689 years,” as in your example, is testament to wonderful holding qualities of this traditional joinery.

I believe that most “deaths” come from poor maintenance, and just as often, from unqualified intervention by novice carpenters of "fix it" folks. This intervention, whether contemporary, or in the chronological history of the frame, can often lead the compromise-demize of the structure, which is often taking more time to happen than the occupants of the structure are aware of.

The “3 way tying” joint in your example is clearly compromised, and has moved apart. Now when we get to your comment about “teazle tenon,” I became a bit confused? “Teazle tenons,” (sometimes call “threading tenons,” must pass through a minimum of two or more timbers, usually timbers perpendicular and/or juxtaposed to one another. I don't see a “teazle” in the photo, unless the tenon on the “lapping jetty” of the “jowel” passes through the “tie beam” and into the “principal rafter above.” I would note at this time that the “jetty” of the “jowel” can sometimes present with a “dovetail” along its side that will fit an appropriate “dovetail” mortise on the receiving side of the “rafter plate” (what you are calling a wall plate.) Have you ever discovered this type in your travels?

Now you of course saw the joint, but from the photo it presents more as a “racking” and maintenance failure over time, than it seems a “rotational” failure. I would agree that it does appear to have had a “novice” repair in its history, which may have included an improper replacement of the “rafter plate,” and the addition of the mentioned “metal strapping.” I often find such metal “reinforcements” added by “novice,” and or “unqualified” restorationists. A very few present as “legitimate” artifacts of the frames history, I agree, and as such preservation may be warranted, yet many more should just be removed, if given an opportunity during a proper restoration, as they undermine the validity of the original intentions of the House or Timberwright that built the structure. As for working...I would have to agree that only sometimes they do subjoin some ancillary security to this family of joints, but many are an unnecessary, an only redundancy if all other factors are addressed.

I agree that many of the engineering analysis of this joint may not be necessary, but the addition of hardware such as strapping is not appropriate for the family of joints when executed properly and with good means, methods and material. I make that statement both as a traditional Timberwright, and as a Restoration Artisan. I see many of these types of frames “modified” with good intentions by folks with perhaps good “timber framing” skills but no background in the ethical ethos of “Heritage Conservation and Restoration,” of architecture. As such, I may (or may not) keep such an artifact in a frame during a full restoration, as my task is not only to honor the original “Wright” of the frame, but to preserve the heritage skill sets that built fashioned this vintage fabric. As such, the metal is an unnecessary redundancy, if all is done well, in most cases.

I will note, that if Ben becomes a “pain in my back side,” (he seldom is or does) and insist that a metal or synthetic moment or drawing connection” is necessary, we will save the “artifact” if structurally sound, or replace with a surreptitious hidden reinforcement.

"Happy New Year" to all,

j

Teazle tenon is clear to me, Jay, your description is clear but goes past my known description of Teazle tenon, it is clearly depicted in HATJ, A Graphic Guide, pt 2 Tying Joints:Tie at Plate.

Rotational forces..... Ken are you suggesting the post is twisted? Or has the plate and post been pushed away from the building directly in line with the tie beam? Rotation as in the whole building? I still suspect rafter thrust. Closer look at the peak of the roof in some detail or at the purling.

The brace below is shown to have been compromised and gaped at the post. Are there other aspects that would point the the Why this happened? Like those common rafters with shadow lines of where they used to rest?

Regardless if it was yesterday or 400 years ago, someone beyond a novice applied the tire rim. It had to have been heated, straightened, holes punched Pins constructed and applied, all with much thought. Sometimes buildings don't demand full on restoration, when a permanent fix will suffice. I speculate that it was a run away cart that rolled away and smashed into the lower part of the post and the reaction was shown at the top of the post. Then they used the, now bad wheel, to fix the damage cause. Maybe the horses were spooked and they had a wreck. Hows that for conjecture.

Hi Tim,

Some of your surmises might not be so far from the mark ! This building was recently hit by a truck reversing into an old coaching door opening on the same side of the building as the broken English tieing joint however this happened a few years after the above picture was taken. The square holes seen in the metal strap are original holes used to secure the tyre to the wooden cart rim.

Maybe my choice of the word "rotation" is not the best since as Jay mentions above transverse racking of the building can in effect cause rotation of the main post about its base. It's probably worth re-examining the drawing where one can see that the main post concerned is a full height storey post of some 16 foot length with this divided into 6 foot on the ground floor and 10 foot on the upper floor. The posts at the jetty are discontinuous being jointed above and below the mid rail. This will not provide the same degree of stiffness as a continuous post. The 2 bay upper room was completely open to the roof and so this room lacked intermediate stiffening other than the cross braces between the tie beam and main posts. I have mentioned a couple of times on this forum of my dislike for empty frames and especially those that comprise just main posts, cross braces, tie beam and pricipal rafters.



The picture above shows the common rafters in the jetty bay immediately in front of the failed tieing joint. Of particular note is the dragon tie between the wall plate and front tie beam. This is a very archaic feature generally found only in timber-frames built within a 1200 - 1300 date range.

Regards

Ken Hume

Ken,

I'd be interested in hearing more about our dislike for empty frames.

Hi Ken,

Thanks again for great photos and this conversation.

You wrote: "This is a very archaic feature generally found only in timber-frames built within a 1200 - 1300 date range."

I would only validate that as perhaps as it may apply to certain timber frames from the U.K. as "dragon" beams have been used extensively for over a thousand years by other wood timber cultures (still are extensively in some) and I believe probably the first to be in ships in Europe and with the Swiss for the first in timber architecture of Europe, David B, could confirm that I am sure.

I also have the same question as David B, on the facet of "dislike for empty frames." I need clarification, as barns are "empty frames" that are some of the most enduring of history? As are many temples in Asia. Did I miss your point on that one?

@ Tim B.

Thank you for using that reference Tim B. about the "teasel tenon," and I agree from that account it would be such, but I challenged that use with several folks on its publishing, and many including Ed (levin) agreed with my confusion.. However, from most other text I have read, and examples I have seen, and all other aspects that I know of from variable sources from central and eastern Europe to Japan, a "teazel tenon," to be such, must pass through more than one member. For now I leave it as a mystery of "British" semantics.

I also did not mean for "novice" to be take to fare out of context or necessarily demeaning, just as, "one not familiar with proper timber frame restoration modalities." I would see such metal as an example of that, and in some times and places it being an asserted and keen effort to conserve what is there until a better solution or full restoration could be addressed.

Regards,

j

Jay,

I am not aware of the use of the dragon beam in vernacular styles in Switzerland. If it is used, it is probably found in cities, and there likely a French influence.
Hip roofs are framed with a very different method than that employing the dragon beam.
Jettying is not overly common, and when employed, the method of framing (Riegelbau/Fachwerk) does not necessitate the use of a diagonal beam.

I am interested, Ken, in hearing about your perspective of the so-called open frame because I am not used to this method of construction.

I see timber frames built in the US as large open frameworks with light framing partitions added, or in many cases what I would consider to be unreasonably large open spaces. This stands in sharp contrast to the framing methods I have learned, where the frame itself is divided and partitioned. Also these buildings are thorough tied together with a multitude of intersecting frameworks. In our customs, even buildings built for strictly agricultural purposes are often subdivided with closed frameworks.

I suspect your reasons for disliking open frames are similar to what makes me uneasy about these structures -blown joints like shown above.