I think there was a talk at one conference, not sure if it was an engineering pre-conference workshop or a regular conference presentations, but the speaker, an engineer, said that the method he used to calculate the spacing of pegs was based on load. He would figure the load and then what size metal bolt would be needed to hold that load and use that diameter for the spacing of the 4D 4D 3D stuff and then place a larger diameter peg that has the same strength capacity as the bolt in that location.

Basically use the metal size for determining the spacing but use a peg for the actual fastener.

I'm not sure if I've explained it correctly or not.
Hope that helps.

That's interesting, Jim. I've never heard that before, but I like it. Do you remember who said that?

That is a correct explanation Jim, I'm going to quote you with a little addendum, hoping for a little more clarity.
"Basically use the metal size for determining the spacing but use a peg (within its allowable design limits) for the actual fastener."

That was presented during the enginering pre-con in Roanoke, I think it was part of Dick Schmidt's presentation. I've heard it from another engineer as well.
The metal connection spacing rules are in Section 11.5 in the NDS. The commentary is available online;
http://www.awc.org/Standards/nds.html

a similar line of thought is presented in the standards for design of timber frame structures. here's what they say:

"3.4.8 Edge Distance, End Distance and Spacing
NDS© provisions for edge distance, end distance and spacing in wood connections with dowel-
type fasteners are based upon the use of steel fasteners. Since a wood peg has substantially
lower lateral load capacity than a steel dowel of the same diameter, the required minimum
detailing dimensions (edge distance, end distance, and spacing) to prevent splitting in a pegged
joint are less than those for a joint with steel fasteners. One approach to selecting appropriate
end and edge distances is to proportion the joint based on the assumption that steel bolts will be
used instead of wood pegs. The bolt size is selected such that one steel bolt has the same
capacity as one wood peg used in the actual connection. Then end and edge distances are
selected based on the steel bolt diameter. Spacing between pegs should conform to the
provisions of the NDS© with no adjustment in fastener diameter. The recommended detailing
dimensions shown in Table C3A have been shown to develop the full strength of a pegged
mortise and tenon connection without splitting of the timber (see References 3 and 5)."

I still don't get the spacing requirements though. with white pine the 4D (where D=diameter of peg) requirement of spacing to the edge would make it impossible to put a 1" peg in anything less than a full 8" wide tenon- or am I missing something in this?

Missing it. Calculate the loads as if you were using a steel bolt to make the connection. Lets assume when you look up the load, species and joint configuration in the NDS tables that a 1/2" bolt would safely bear the load. 4D would be 4x1/2" for a 2" edge distance. Now use your 1" peg 2" off the edge. If the table shows that a 1/4" bolt will do the job then your minimum edge distance is 1", etc. The edge distance guidelines were so a bolt wouldn't split out the side of the joint, They assured that adequate meat was left around the bolt. That distance doesn't need to be greater than the bolt's requirement just because you chose to use a larger dia wooden peg. Making sense?

ahah! i see it. so lots of meat in the tenon if we calculate D from the diameter of the bolt. reading at work - thinking effected by metal desk.

now it is calculating wind lift on the porch roof - would this be divided by 3 if there are 3 post to plate joints?- deciding whether 1 or 2 pins (people up here in northern ontario are using 2 there) then dividing the lifting load per joint by 1 or 2, determining the proper sized metal bolt in the tables to bear that load, then using that diameter to set the wooden pin spacings...

i have a feeling there is a translation between materials here that speaks to a impasse between objectifying and traditional forms of knowledge.

i wonder just how much it matters if a tenon splits in a blind mortise? the peg may go loose perhaps if it does, but once it's lifted up, the joint is not going to fail in tension from windlift. or is this too gonzo an attitude? the ends of tenons may very well split irregardless, just living out their lives however they may.

Hi Toivo,

Excellent question. You now know what you don't know.

That is a huge step forward.

Regards

Ken Hume

Thanks to DonP for clarifying what I was trying to say. And posting the link.

Will someone please enlighten me.
Are we comparing a tightened nut & bolt fastener to a wood pegged mortise & tenon joint or just a smaller steel peg to a larger wood peg in a common mortise & tenon joint?