exploring a new method of framing....

[Thehardway]

For many people, the availablilty of solid sawn timbers over 6x6 is dismal.  Additionally many inspectors will not permit the use of any lumber which is not grade stamped.  Additionally the weight of large dimension timbers can be prohibitive in many situations.

I am exploring a hybrid framing system to address these issues and seek comments and input on what people think.

The system would use traditional mortice and tenon joinery but with built up 2X dimension lumber rather than solid timbers.

Joints could still be pegged in traditional manner.  Joints could also be made in an interlocking fashion which could not be done with traditional solid sawn timbers adding to strength and visual interest.


For instance, lets say you wanted to build a kingpost truss with a  40 span.  It would be virtually impossible to find a 10"X 12" X 40' tie beam.  You could however get 2x12"X 20' grade stamped dimension lumber from a local big box store.  You could build up 7 of these to compose the width of the tie beam and use 3 alternating center plies along its length to make the span and tie the kingpost in.  The buildup would be done with screws and then once assembly was complete, thru bolted with carriage bolts at intervals.

I have seen wooden roller coasters built using this technique.  It is extremely strong.

There is no drilling and chiseling needed to make mortices and tenons, all mortices are saw cut into the 1.5" board that is receiving them and then the neighboring boards form the walls of the mortice. They could also be done in a half lap style if so desired.  Tenons are all 1.5 and placed in the saw cut morticed and then locked in by the next ply.

The use of dovetail joints would be very effective.  Beams could be built in place.

[beenthere]

Good idea. The beams would have more strength when laminated (assume you would glue them as well) in the same sizes than solid, mostly due to the random location of any strength-reducing defects.

A problem to overcome is that the grade stamps may be hidden from the inspectors view (which can and has caused problems in some applications). Some inspectors can't think beyond the printed words in front of them.

A traditional "look" might be the only drawback. Then again, few people would know the difference.

[MHineman]

A traditional "look" might be the only drawback. Then again, few people would know the difference.

How about after being inspected, box the "timber" with 3/4" by full width boards.  Miter the corners where the boards come together.
  Most will never see the miter detail and it will definately look like a full size timber from a distance.

[Jim_Rogers]

Do you have a structual engineer in your family?

You'll most likely need one to layout all the screw and bolt locations to meet code(s).

Doing this wrong is worst then building with undersized timbers. I have posted photos of failed "post and beam" constructions that some do it yourselfers thought that they could do. Placement of the bolts is very important and it is in itself a very strict science. Or they'll end up splitting the wood when the load is applied.

Here is one example.



And "field gluing" of planks together will most like not meet code either. They would have to be certified by some one and without complete control conditions of the glue, wood, pressure used to bind them while drying, and probably a lot of other reasons I don't know about it would seem unlikely to me that anyone would approve the process. And if not approved would be as if it wasn't even there or done.

Basically what you're talking about is a "home made" glue lam.

Personally I tried that many years ago. I didn't however, at the time, understand the loads that would be placed on my "home made" built up timbers, and they began to sag shortly after I raised them and started putting on the roof rafters to make my own sawmill roof. And they sagged to the point were I thought it was very unsafe to have them up in the air. And they came down.

I really don't or didn't want to rain on anyone's parade but if it was that easy then lots of people would be doing it and it would be a very common thing.

You'd be better off doing the steel collars like Arkansawyer did when he built several out buildings. This type of construction would be better in my opinion.
Do a search for his posts in this section and you'll see some of the things he had welded up to join timbers together. (Or he welded them up, not sure without doing the research myself.)

Jim Rogers

[grweldon]

Jim,

I am not a structural engineer, nor do I claim to be a builder of post and beam construction.  I sincerely acknowledge your experience and wisdom concerning this type of construction, however, I am a manufacturing engineer and a tool designer.  Looking at that photo of the failed joint above, something just doesn't look right to me.  The location where the bottom member joins seems to be incorrect.  Would it not have been better to place the joint directly under the vertical member that the plate is holding and then fasten all members with bolt holes that were offset from center slightly?  Also, although it wouldn't look as good, would it not also be better to can the metal plate in favor of a plywood plate that would be glued and bolted with smaller screws, possible 1/4 to 5/16?  I don't really know, I'm just trying to reason this out...

[Jim_Rogers]

gr:
That is my point exactly.

It has to be done correctly.

That failed joint picture was sent to me by a structural engineer who was called in to help them solve the problem of the failing joint.

You can't just put something up there and hope it will work correctly. It has to be designed and all the loads and load paths have to be understood and accounted for.

I'm not a structural engineer either. I have my work/designs reviewed by one of many that I work with to make sure that they are correct.

Jim Rogers

[Thehardway]

Jim,

Thanks for chiming in.  I'm not proposing anything like the picture.  In fact what I am proposing would be just the opposite.  There would be no butt joints or bolting plates like that.

Post and beam uses a lot of point loading.  What I want to do is load distribution over the entire span.  In the case of a post, at least one member would be continuous across the top of the post and reach to the midspan on each side.  It would be held to the top of the post with a tongue and fork type joint.  I really need to draw this up.

In cases of extreme stress, a flitch plate with bolts and compression washers would be used only to clamp the members together tight, no plates at endpoints where splitting or end grain tearout is an issue.

I know this would need to be engineered.  The hope is that some standard load/span tables could be developed.

Joints would be wood on wood in typical TF joinery arrangements but faster easier and more accurrate to cut for the beginner with less specialized tools.

[losttheplot]

My neighbor used the method I think you are describing to build his wood shed.
For small buildings I think common sense goes a long way.

For large buildings a qualified opinion would be advisable what ever the methods used.

[D L Bahler]

For similar reasons, I have long thought the German system of Riegelbau (or Fachwerk) to be an excellent solution. This is a 500 year old timber framing method that uses small timbers -posts around 4x5 inches, and very little above 8 inches is needed. Also, everything can be made well out of short lengths of timber.

The system works by handling the loads with many smaller timbers, rather than a few giant ones, while still using traditional cut joinery to tie everything together

[losttheplot]

If you take the timbers out of timber framing..... it kind of loses the plot............ ???

[Chilterns]

Hi,

There is something about this approach to utility building construction that is quite appealing to me.

It could also be used in proper timber frame construction to create either wall frames as shown above or maybe better still as bents which when combined with splined interconnecting girts, plates and sills could result in a timber frame of much higher load carrying capacity than a traditional mortice and tenon frame.

Laminated timbers generally have a greater load carrying capacity when compared with sawn lumber because the quality of the timbers that form the laminations is fully known i.e. selected material with minimal defects or with those defects positioned within the lamination build up so that this will not affect the overall load carrying capacity of the timber assembly in service.

It would be important to use nearly dry planed all round timber so that shrinkage would not have any significant effect on the assembly. Some modern adhesives actually require a degree of moisture to help with settings.

It would be interesting to hear from someone with good experience in using laminated timbers in respect of this proposal.

Chilterns   

[Thehardway]

The pictures posted by "lost the plot" are very close to what I am talking about.    In many cases a hybrid approach could be used.  Conventional solid sawn timbers for posts and short members such as braces and the multi-ply members for longer spans.

I hesitate to use the term laminated as it implies glue and I do not advocate field applied adhesives because of all the variants in the results.  Temp, humidity, dust on surface etc. 

I like the joints pegged in a traditional style after assembly.