I live in California and I am trying to gather stats on the strength of mortis and tenon and dovetail joints vs. plates and bolts. If anyone knows of any studies or publications that could provide some clarification I would appreciate it. We live in a seismic four area and I am wondering if the codes will allow a strictly traditional construction.
thanks

Reports on research performed at the University of Wyoming related to pegs and mortise & tenon joinery are available for download from the Members Only page. A new report on the response of full-scale frames to lateral loads will be released soon (maybe this summer). In the mean time, take a look at Timber Framing issues 62 (Dec 2001) and 63 (March 2002) for short articles on one- and two-story frame behavior. Issue #63 also contains a discussion (in the Q&A section) on the suitability of timber frames for seismicly active areas. Basically, the strength of a traditional timber frame is adequate to resist seismic loads, but you'll probably need a lateral load system, consisting of SIPs or conventional shear walls, in order to satisfy the stiffness requirements.

Hi Dick,
I saw your articles in TF62 and TF63 and had a couple of questions for you. Please excuse me if I misstate something here, as I am going from memory.

When I look at a tree I see something strong but not especially stiff (bends in the wind). As timbers dry they increase in stiffness. Does your report take this into account, are you able to calculate or predict stiffness vs. moisture content?

Didn't your testing involve both the use of spline joinery and traditional mortise and tenon joinery? Did the data suggest any advantages one way or the other?

How about frame stiffness vs. brace length? I know that longer braces are better, the question is just how much better?

I realize that to perform destructive testing on full size frames is a significant and expensive undertaking, is it possible to get good data using scale models?

Finally, I don't want to throw too many variables into the mix but perhaps in the future you could include southern yellow pine in your testing.
Thanks,
Chip Piller

Chip,

The frames we tested were basically seasoned. EMC in Laramie is about 6%, so things dry out pretty fast here. It might be possible to predict stiffness as it varies with MC, but it wouldn't really be useful for frame response. Actual member stiffness is not really that important. The joints themselves make up the lion's share of the displacement of the frame under lateral load. Natural looseness of the joint, bending and shear flexibility of the peg, and localized crushing of the base material all contribute more to frame deflection than bending of the frame members themselves.

Our objective was not really to evaluate the relative merits of different joinery styles (splines vs. M&T, etc.). We wanted to develop analysis models that can be used to predict response of whatever joinery was used. In general, from a strength perspective, you'd be better off to use splines rather than M&T joinery, assuming that the splines fit into the frame (You don't want them sticking through an exterior wall adjacent to a post). Using splines makes it easier to guarantee that you have adequate spacing and end distance on the pegs and also avoids the problem of tension perp. loading of the post.

You're correct that longer braces are better (stiffer). The question is just how much better can be answered by doing a parameter study using structural analysis models (normally computer programs). Again, the results of our work will help you do that study by giving reasonable values for joint stiffness to plug into the analysis models.

We haven't done any work with scale models. They would certainly require less material, but the time required to cut them, test them, analyze results, etc. would probably not be affected signficiantly. Also, with full-size frames, we avoid questions about the scalability of the results.

Our joint tests (see the Joint Report and the Long-term Report) included SYP. Good stuff!

Thanks for your interest and questions.

Dick