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RE: heavy timber frames[Subject Prev][Subject Next][Thread Prev][Thread Next]
- To: seaint(--nospam--at)seaint.org, GordonGoodell(--nospam--at)harmonydesigninc.com
- Subject: RE: heavy timber frames
- From: Tim Rudolph <TimRudolph(--nospam--at)att.net>
- Date: Fri, 03 Jul 2009 16:05:54 -0700
Gordon, For strawbale construction the California Strawbuilding Association CASBA - has done testing on strawbale walls and is working on determining a R. It seems when the Strawbale Guidelines were adopted in California in 1998 & 2002 the R that was assumed for stucco plastered strawbale shearwalls fit in the 1997UBC tables as R=4.5 but not explicitly stated anywhere. the shear value seemed to come from the code value for stucco over wood framing that no one I found has any memory of testing for the 180plf per skin value.(see the California Strawbale Guidelines) CASBA and the Ecological Building Network (www.ecobuildnetwork.org)did full scale testing of walls. that data is available for download. At this point it seem the strawbale shearwall assembly would earn a R=3 due to the limited number of test. also the allowable shear will be adjusted based on plaster compressive strength, mesh reinforcement gauge, plaster thickness and aspect ratio. The R=3 will keep the wall at or below the ultimate load and elastic in performance. The work is underway now to determine the path to apply this into the current code structure. If you look at how plywood shear walls got the R=5.5 or 6 when the walls become inelastic at R=3 (the typical safety factor applied to plywood shear walls is 2.8- 3.0) the R is determined by an inexact method when applied to traditional building materials where with new systems lots of science is applied to determine the R (look at steel plate shearwalls R and data on a new material acceptance) I think a standard is being written to address how to determine a R for a structural system. If more info is desired contact me Tim Rudolph Bishop CA So what about straw bale houses? Adobe? Rammed earth? Earthships? What do we do, say "I have no data for or confidence in the system, so I'm going with R =3D 2"? For straw bale construction, I've seen = engineers use values ranging from R =3D 2.5 to R =3D 6. It makes a big = difference!
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