Log Connections

[Engrman]

Does anybody have any details on log structures? Project is a house, post and beam roof structure, with varying log diameters and lengths. How to account for shrinkage across diameter and length, beams and columns? Supplier says logs will have less than 15% moisture content but up in the mountains that means still some significant moisture loss. I'm thinking connections must have some means of taking up slack once shrinkage starts but must not restrain shrinkage from occuring. Sounds like a tall order to me.

 

[RockEngineer]

I do a lot of engineering for log homes. There is usually very little shrinkage in the logs longitudinally but there can be significant shrinkage in the logs radially. If your supplier is providing logs with less than 15% moisture content you need to know if this is the surface content because they have tried to kiln dry them or if they are standing dead trees with this low moisture throughout. This will make a difference is the actual radial shrinkage.

If you are only doing a post and beam structure with the logs there should be minimal shrinkage to consider. The main shrinkage is when you have log walls laid on their sides so you have lots of radial shrinkage to consider. When you have lots of wall shrinkage you tend to use jacking screws on your columns. If you provide a fax number I can provide more details.

 

[Engrman]

Phone number is 719-533-1725. Call first so I can switch over to the fax. Will require 2 phone calls. Sorry. Thanks for the help.

 

[LarryGlickfeld]

LOG STRUCTURES: Log Wall design for concentrated and lateral Loads: While these are typically issues we deal with in just about any log structure, I've never seen any "textbook" examples of how this is done.
For concentrated loads on walls, we typically resort to wood or steel columns -- perhaps within the log walls -- at some point, but how can we determine the actual concentrated load this stack of logs is capable of supporting? Obviously, it depends on the log size and species, construction method, location of openings, etc.
Re. shear wall, spiked walls are mechanically connected from one course to the next. What about through bolt walls? Do we figure some kind of friction, or what.
Anyone have any ideas, or sources?

 

[RockEngineer]

See thread337-25324 for ideas on calculating log shear wall strength. For concentrated load capacity you need to look closely at the construction method and the length of wall section. Short sections of stacked pieces of logs tend to roll and buckle if used as columns but long wall sections usually are pretty stable and that stability is greatly increased if there is a notched or butt & pass corner. If you are using coped logs you usually gett a pretty good fit for bearing one log to another. If you are using full round logs with pounded in rebar as the separator/connector you have to look at the capacity of the rebar because the logs will tend to shrink away from each other leaving the rebar to take the load without logs bearing on each other. Each construction method has its advantages and disadvantages.

 

[LarryGlickfeld]

CONCENTRATED LOADS ON LOG WALLS: Obviously this depends on the variables: log size & species, length of wall section, the corner construction (or lack thereof, e.g., if there are doorways, or window openings, or occasionally interior walls with no corner(s)), and the actual wall construction (spiked, thru rods, etc.). But given the variables, where does one go? As far as I know, there is no research, testing, or textbook dealing with this issue, yet it is one that comes up on a regular basis with log wall construction.
I think most of us go with the "when in doubt, provide a steel column within the wall" rule, but obviously there's a better way.
Occasionally I will use an analogy with reinforced concrete, i.e., the logs take the compression, and the rods or spikes take the tension. But with the individual log courses, this isn't exactly a very accurate analogy.
Does anyone know of any published information on this subject.