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Re: Adding nail values to bolt values

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I now agree (from different posts to my original question) that the two should not be added.  But, it seems from your reply that you think my problem stems from a conventionally framed rafter system with rafters and collar ties.  It is not (if that is what you are thinking, which may be from my poor explanation), but the framing is made up of site built trusses.  they are made up of 2X6 top and bottom chords and 2X4 webs with plywood gussets at the panel points.  We've had these discussions before on the list about site built trusses, but that is what I have.  These trusses (as I have stated the ones that are still in one piece) have worked very well for over 30 years.  I think that they may have been engineered, but back then there wasn't a building department here, so no plan reviews.  I suspect there was never a snow load in the original design (If there was one), because otherwise things are close to "calcing" out with dead load only.
The boss will just have to go with metal plates and bolts or replace the trusses all together (as I have already suggested as there is not that many of them.  That suggestion was rejected).
Thanks for your reply,
----- Original Message -----
Sent: Tuesday, March 15, 2005 6:50 PM
Subject: Re: Adding nail values to bolt values

Bill Allen, S.E. wrote:

Joe ?


Even though bolts and nails are ?dowel type fasteners?, I would hesitate to combine their capacities. After all, holes are drilled for bolts whereas nails are ?interference fit? type of fastener. In effect, the nails have to fail before the load is transferred to the bolt. Mixing different diameter of bolts makes more sense, although I wouldn?t do that either.


Sleep well at night or make boss happy? Hmmm?.


T. William (Bill) Allen, S.E. (CA #2607)


Consulting Structural Engineers

V (949) 248-8588


F (949) 209-2509



Bill Allen always claims that we don't agree but for almost a year we have agreed on quite a lot (but I've been at fault for now keeping my personal frustration under control). In this case, Bill's advice is very sound. You can not mix the strength in shear of various "dowels" or bolts and nails. Obviously, the nails will fail in bending first then the total load is transfered to the next stiffest material - the greatest diameter bolt.
The old issue that Bill points out to is the fact that conventional construction only requires about four 16d nails at the connection of each tie, but when you run the numbers it rarely balances. However, if you use through bolts, then remove the nails and keep the diameter of the bolts consistent. If you do this refer to the AITC manual (or NDS) and maintain appropriate edge and end distances and the spacing between rows and columns of bolts. I just don't think you have much room if the chords are 2x4 or even 2x6's for the top and bottom chords and the struts.

Heavy timber can use more elaborate connectors that most engineers don't consider out west - shear plates and split rings. So it depends on the thickness of the truss material and the area of overlap that can allow you the appropriate clearances.

However, as much as I hate to admit that I agree with Bill Allen ;-)  the truth is that he is right on the money here and I would not deviate from his advice.



Dennis S. Wish, PE
California Professional Engineer
Structural Engineering Consultant


760.564.0884 (office - fax)

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