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Pegged Connection - Design Solutions #35971 11/14/22 07:24 PM
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JohnnyB Offline OP
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Hello -

I am relatively new at timber frame engineering but I am really enjoying digging into the engineering and providing solutions for my clients. With that being said, this particular post is about providing solutions when the pegged connection is the weakest link and a reasonable/industry standard solution for the issue. To preface this issue, and the solution I have been providing t my clients, I have assumed the shear wall resistance is negligible for these when providing lateral resistance against earthquake and wind loads. The main reason is that the architect / contractor / owner does not provide the exterior covering that is planned for the job: OSB, SIPS, etc. Therefore I have to make conservative assumptions, i.e. negligible lateral resistance. I know this is an important part of the resisting system for the structure, but it doesn't change the question of how to provide a solution to this particular issue.

I am calculating the failure modes based on TEFC paper by Joe Miller from FTE, Capacity of Pegged Connections. This paper is well written and based off of the TFEC-1-2019-standard-&-commentary. I have noticed that the pegged portion of the connection often shows insufficient capacity in failure mode V with a standard M&T connection with two equal cheeks. This failure mode shows insufficient capacity based on the shear strength of the peg. I find that when I use the specific gravity of steel it easily passes, so I have been specifying steel dowels in place of normal wooden pegs.

A couple questions:
- Is this standard practice within the industry?
- How have others solved this issue when encountered?

All feedback is appreciated, thanks!

Re: Pegged Connection - Design Solutions [Re: JohnnyB] #35972 11/15/22 03:59 PM
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Joe Miller Offline
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Mode V failures tend to be as much a deformation limit as the wood fibers in the dowel are deforming - so the capacity limit is set at the load after deformation equal to 5% of the dowel diameter. In a braced frame situation with tension joinery, this deformation can end up causing larger deformations within the structure than calculated. As such, it is most common for timber frames, if they are being enclosed by some building envelope (stick framed walls, SIPs, board and batten siding, etc), that we rely on the building envelope to take all of the lateral load via shear walls. The adage "load goes to stiffness" holds true, and, while the braced frame may be able to resist quite a bit of lateral load at an ultimate level, it tends to only engage that capacity after quite a bit of deformation, and, the exterior walls are a stiffer, and therefore the preferred, load path. In seismic areas, this is also quite a bit more favorable, as the ductility of nailed shear walls is substantially more defined than that of a braced frame, and thus we have much better response coefficients.

If you are designing mortise and tenon joinery using steel dowels, then utilizing the the design parameters of pertinent design code (NDS, CSAO86, etc) for a bolted connection would be the appropriate methodology. The edge/spacing/relish detailing requirements within TFEC 1 are based on a wood peg, and, would be quite unconservative for a steel dowel.

Re: Pegged Connection - Design Solutions [Re: JohnnyB] #35973 11/16/22 01:37 PM
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Jim Rogers Offline
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Joe Miller, thanks for your reply.

Jim Rogers


Whatever you do, have fun doing it!
Re: Pegged Connection - Design Solutions [Re: Joe Miller] #35974 11/16/22 09:21 PM
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JohnnyB Offline OP
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Thanks Joe. I appreciate the feedback.


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