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RE: heavy timber frames

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Title: heavy timber frames
Gordon:
 
For traditional timber framing (i.e. mortise and tenon/pegged joints) or even "psuedo" traditional timber framing (i.e. made to look like mortise and tenon/pegged joints but actually drift pins and steel knife plate, etc), I will NOT use the timber frame for seismic lateral loads and will only use the timber frame for wind lateral loads in rare occasions.  I will use some other lateral system (typically either stick-built or SIP shearwalls).  While there is certainly some stiffness for a traditional timber frame joint, there really is not solid research or information on how do treat such joints for seismic loading.
 
The TFEC 1-07 Standard (Timber Framing Standard) kind of does not really directly address the issue.  It merely states:
 

"4.1 Stand-Alone Timber Frames

Stand-alone timber frames have been shown to have limited stiffness under lateral loads due to

the relatively low stiffness of wood-pegged joints. Hence, the effects of joint stiffness shall be

considered in the structural analysis of stand-alone timber frames to assure that the strength and

serviceability of the structural system are adequate for the intended end use."

Hope that helps.
 
Regards,
 
Scott
Adrian, MI


From: Gordon Goodell [mailto:GordonGoodell(--nospam--at)harmonydesigninc.com]
Sent: Thursday, July 02, 2009 2:24 PM
To: seaint(--nospam--at)seaint.org
Subject: heavy timber frames

For those of you who deal with heavy timber construction and traditional timber framing, what response modification & overstrength factors do you use?

More globally, when you get into weird or new systems that arent listed in ASCE 7 Table 12.2-1, how do you deal with it?  In many cases you could pick a similar system and decide if the factors listed for that system are reasonable for yours, but when youre talking about ability to perform into the plastic range its a lot about confidence, and a lot about having seen how these systems have survived real earthquakes.  If you were designing the worlds first stick-framed house, how could you quantify ductility and overstrength?  You could do it for the materials in a lab, and then try to extrapolate those data to your framed system as a whole, but youre not just talking about wood...its also steel, interactions between materials at connections, etc.  Think about how hard it is to calculate the deflection of a wood diaphragm...the assumptions overwhelm the results long before youve got a number to hang your hat on.

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 Im going with R = 2?  For straw bale construction, Ive seen engineers use values ranging from R = 2.5 to R = 6.  It makes a big difference!

Just wondering how any of you deal with this if & when it comes up.

regards,

Gordon Goodell