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RE: Log Buildings

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Hello Paul,

There are typically 2 connections used in Anchorage for lateral design:
drift pins and full height threaded rods [spikes are not popular because of
shrinkage problems]. Normally the designers assume the wall piers carry load
in proportion to how long they are [based on number of drift pins].
Normally full height rods are provided for overturning moments at the pier
ends and wall corners. I have seen some designs where the designer assumed
the logs span to perpendicular walls.  This can work for a smaller building.

1997 UBC 2318.5.1.2 indicates dift pins can be designed for 75% of the
capacity of in bolt tables and additional penetration of the pins should be
provided in lieu of the washer-nut.  

Pay attention to hole tolerances, often holes are overdrilled and NDS 8.1.2
indicates bolt holes should not be larger than 1/16" of the bolt diameter.
If all the drift pin holes have a 1/4" play, it would add cumulatively up
wall when considering potential drift dispacements.

The main problem I see is the connection between the foundation and the
bottom log on platform framed floors. Sometimes designers have argued that
full height threaded rods running through a joist cavity will provide a load
path to the foundation.  The holes through the floor sheathing and sill are
overdrilled and unless the load is transmitted by air resistance I cannot
see the loadpath.  A framing anchor from the bottom log to the rimjoist and
from the rimjoist to the foundation sill plate is an easy solution.  

Also log walls are heavy and could have large out plane loads and the
connection of floors and roofs to walls for out-of-plane loads should be
considered.

My Building Department sells a 20+ page booklet of example loadpath details
for $5.00, titled peculiarly enough "Load Path Details". Three pages show 8
log wall connections and a typical elevation.  You could call the MOA permit
counter here and try to order one [907-343-8347].  


Respectfully,

Scott M Haan 
Plan Review Engineer
Building Safety Division http://www.muni.org/building
Development Services Department
Municipality of Anchorage
phone:907-343-8183  fax:907-249-7399
mailto:haansm(--nospam--at)ci.anchorage.ak.us



-----Original Message-----
From: Paul_Reilly(--nospam--at)dot.ca.gov [mailto:Paul_Reilly(--nospam--at)dot.ca.gov]
Sent: Friday, April 06, 2001 6:54 AM
To: seaint(--nospam--at)seaint.org
Subject: Log Buildings


'Log cabin' style buildings, ripped 12" lodge-poles, stacked & pinned:  I
am curious if this bearing wall system has any published allowable
capacities for shear.  5/8" A307 lags are staggered at 24" OC each parallel
course.  I would appreciate any lateral design criteria for this building
system.  THIA.