Need help with log cabin calculations

[Don P]

I'm not a real fan of recesses in the tops of logs. In conventional construction you assume the siding will at some point leak and joinery taking advantage of gravity is your first line of defense against that water doing damage. I assume at some point the lateral will have water in it. An upward facing groove can trap moisture. The handcrafters now advocate a top kerf so take it for what its worth.

Their section on settlement does a better job of describing the factors that come into play with shrinkage and settlement than I have been able to. Notice different forces can be at work in different types of construction.

http://www.logassociation.org/resources/standards.php

That short section is now being written into about 20 pages of building code that will most likely be law by the end of the decade. It includes provisions for shrinkage and settlement in milled logs with relatively wide, relatively flat, bearing surfaces. The section dealing with handcrafted log settlement is a bit more detailed dealing with compression and spreading of the cope, 2 more factors that come into play in its settlement equation.

Below are some short excerpts from the proposed code addressing settlement. I posted the basics of this about a week ago and had to delete it all after a response, we apparently lost a good member in the process. I hope he returns. That is not my intent, I do feel everyone does better work when they understand the facts surrounding their work, so I'm trying again. The fault could well be my own for not presenting the info in a third party officialeese. These 2 references give the information in that form. I don't mind discussion or disagreement, just keep it civil.


304.2.1 Total settling. Total settling shall be calculated using the following equation:
?t = ? SL + ?c + ?s

Where:
? SL = settling due to slumping?
?c = settling due to compaction
?s = settling due to radial shrinkage

Exception: Where the minimum allowance for settling is accommodated at 6%.

304.2.2 Settling due to Slumping (? SL).
Settling due to Slumping (? SL) shall be determined as described in this section.

304.2.2.1 Continuous contact.
Where longitudinal seams (joinery) between logs are horizontal (e.g., flat-on-flat, tongue and groove, etc.) or have continuous contact (e.g., the radius of the cope equals that of the log beneath), ? SL =0.

304.2.2.2 Non-continuous contact.
For wall systems where an air space is created and contact is at an angle, settling due to slumping shall be determined in accordance with the provisions of this section.

304.2.3 Settling due to Compaction (?c).
Settling of log walls due to compaction (?c) occurs when the load applied along the bearing (contact) regions of one log to the next are initially insufficient and crushes wood fiber. This is permitted in lieu of the AFPA NDS design requirements for bearing (Section 3.10) when the compaction is part of the joinery design. Settling due to compaction (?c) shall be determined as described in this section.

304.2.4 Settling due to Dimensional Change (?s).
Settling of log walls due to shrinkage(dimensional change in cross-section, ?s) shall
be determined in accordance with one of the methods provided in this section.

304.2.4.1 Tabulated settling due to shrinkage.
Allowances for settling due to shrinkage shall be as provided in Table 304.2.4.1 by climate zone, initial moisture content (MI), and shrinkage coefficient. Refer to the Climate Zone Map included in Figure 302.2.2.4 (from the 2004 IECC Supplement) for a representation of geographic variation in outside equilibrium moisture content.

304.3 Accommodating Settling.
Log structures shall accommodate calculated settling.Calculated settling accommodation shall be clearly stated in the construction documents at each location of involved height.
Exception: Log wall systems where ? t is less than or equal to 0.5% of the involved
height (HI) to a maximum of ½ inch.

[Stephen1]

Don, this will give something to read over the next couple of days.

[Don P]

Thanks Stephen,
The ILBA standards are easy to find at the link above. The proposed code standard is I believe now out of the public view. The public comment period ended shortly after I posted a thread on it last year, and it was taken offline while they review. I do have the draft on my computer, its a little under 1.5 megs in pdf.  PM me an e-mail if you want any or all. You can also try the icc website and their search, it was titled ISLOG.