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Re: Log Construction questions

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John

I have not seen any specific capacities for the joinery.  This varies
considerably from log supplier to supplier as well as log type. 
Typically, I use drift pins driven though one log into the log below and
base the capacity on the principles of single shear connectors in NDS. 
Overturning on the wall panels needs to be reviewed carefully.  Usually
the only vertical through tie that can be used for tension is all-thread
rods at the ends of the total wall.  These are often used to pull the
logs together as they shrink but can be used for the tension as well.

Due to the shrinkage in the logs using interior partitions as shear
elements has to be done with great care.  The shrinkage can be 6" or
more which also needs to be accounted for at any interior supports to
prevent sloping floors.  Interior posts are normally supported on
adjustable screw supports that can be lowered over time.  As a result
most interior walls are provided with a slip connection at the top.

The indicated shrinkage is very real.  It will depend on the species to
an extent.  I know of one house that has at least 6" of chinking and
caulking beneath the log that runs over the top of the framed doors
because the builder did not provide anything more than a standard shim
space around the frame.  Getting kiln dried logs would be out of the
question.  The possibility of aged logs is a maybe but not likely since
the logs would have to be held onto for a number of years in a covered
environment to allow natural drying.

> "John H. Cato, jr., R.A." wrote:
> 
> Folks,
> 
> I'm assisting another architect on a log home (duplex, actually) and
> need to ask a few questions.
> 
> 1) Information on engineering for lateral wall strength.  Are there
> any quantifiable info sources or data on how much the notched joinery
> can withstand?  I've found some 'log building standards' at:
> 
> http://www.logassociation.org/resources/index.html
> 
> .. that gives some basic 'rules of thumb' - but I would like more (and
> don't really see anything like this within).
> 
> I notice recommendations about distance between windows, doors, etc
> (below which the wall is weakened - understandably).
> 
> 2) Wouldn't it make sense to utilize some of the interior walls as
> shear walls to 'beef up' these exterior log walls -- (even simply
> utilizing 45° 1x diagonal sheathing - exposed, on both sides of
> intersecting walls - as a design element on those walls framing into
> the exterior walls).  We have a common wall separating the duplex
> units - to be log construction - and, by notching this connection,
> will gain some strength here.  Other than that, the structure is
> basically rectangular (40' x 70') with no other 'natural'
> intersections to build strength along the eave walls.
> 
> The roof is framed with standard 2x lumber trusses - so thrust loads
> from roof framing is taken care of thru the truss.
> 
> 3) I am finding settlement and shrinkage issues (see above
> 'standards') talking about 6% settlement of the logs over the initial
> (5) years.  That translates into something approximating 6" over the
> 8' (+-) wall height.  I'm not particularly concerned with detailing
> (particularly interior partitions) to handle this - but are these
> numbers rational?  I'm not doubting it at all - but just need a
> broader perspective here.  We're talking 'green' logs (at least,
> that's what the owner has mentioned - he's planning on setting up a
> planing mill to do his log machining).  Log profiles are basically
> rectangular (out of 8x8 actual cross section) with radiused exterior
> face and tongue and groove interconnections (3/4"x1") - log-to-log.
> Would kiln-dried stock be better?  According to the standards above,
> it doesn't hardly matter.
> 
> 4) Connections between log-to-log: I assume any of several mechanical
> connections are workable - pegs, spikes, lag bolts, etc - but I can't
> find any real recommendations on spacing / angling, etc.  It would
> seem some good 12" or so spikes every few feet or so would work - but
> am I overlooking something?
> 
> Any of you fine folks out here got some extensive log building
> experience that you could pass along?
> 
> Thanks.
> 
> -- john.
> 

-- 
++++++++++++++++++++++++++
Forrest T. Braun, P.E.
BBFM Engineers, Inc.
Ph (907)274-2236
Fx (907)274-2520
Anchorage, Alaska
http://www.bbfm.com
++++++++++++++++++++++++++

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