For the Prosper Junction log home build, the log walls and roof joists are pinned together by 3,000 feet of rebar!  Most people are familiar with reinforcing steel, commonly called “rebar”. It is used in bridges, buildings, skyscrapers, homes, warehouses, and foundations to increase the strength of a concrete structure.  It adds enormous capacity to resist loads that cause tension and bending.

It is rarely used in constructing log walls, which is one of the reasons this home is so unique.  It’s all about the rebar for load transfer.  The design of the structure above the foundation must consider all vertical and horizontal loads imposed.  As it turns out, the controlling design loads for this build result from resisting the weight of the building, the wind, and the snow.  In Larimer County Colorado, building code requires the structure to be designed to resist a 156 mph, 3-second wind load and a 70 pound per square foot snow load. These design loads create very large bending and shear stresses that rebar can easily overcome.

The rebar helps to resist the vertical and horizontal loads that the log structure will experience.  For every course or layer of logs, there is a vertical rebar spike that is located every 2 feet on-center.  The length of the spike depends on the size of the log.  The top log is predrilled the same diameter as the rebar.  In this case, ½ inch.  The rebar is advanced through the top log and halfway through the bottom log. The bottom log is not predrilled.  The vertical spikes occur every 2 feet on-center.  At the corners where a butt log meets a pass log, a horizontal spike is driven through the pre-drilled pass log into the butt log.  The length of the horizontal spike depends on the size of the log.  For our home, the vertical spikes are approximately 18 inches long, and the horizontal spikes are approximately 24 inches long.

For the bunkhouse, all pins were advanced using the John Henry method.  A 10-pound sledgehammer!  Realizing that if sledgehammers were used on the home build, nobody would have any shoulders or elbows left by the end of the project.  So, we modernized!  I bought a 70-pound demo hammer to advance the rebar spikes.  Still a lot of work, but not quite the workout as a 10-pound sledgehammer.

Another added benefit of using rebar pins instead of conventional log notch and joinery connection is the structure does not settle due to log shrinkage.  The vertical compression load is transferred through the rebar pins.  Very little load transfer occurs from wood on wood contact.

Doug

 

 

70-pound demo hammer advancing vertical rebar pins
Rebar crew – finely tuned European sports car!
Vertical and horizontal pinning almost complete.
Structural corner detail with horizontal rebar pins.
Structural detail with vertical rebar pins.

 

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