Log cabin Seismic design 1

[GVCivilGuy]

Switching over to the new code (CBC2007 VS UBC 1997). What seismic response modification coefficient (R) should I use for a bearing wall system that is designed out of logs? I can't find anything in the ASCE7-05.

 

[msquared48]

Most log cabins are not a true bearing wall system in that the loads are transmitted through the logs in bending to the intersecting corners. Many have gaps between the logs, but some do not. That being said, with the rods and spikes to transfer the lateral shear between the logs, and the rods to serve as holddowns, I just design them as a shearwall system.

In reality, if you model them on the computer, you could rationalize that they are really log moment frame systems with the rods and load bearing points serving as couples to develop the moment.

To keep things simple, I just use 6 or 6.5 for R (ASCE& or IBC). Never had my analysis questioned in ten years of doing them. Maybe because plans checkers really don't understand these animals very well?

Mike McCann
MMC Engineering