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RE: heavy timber frames[Subject Prev][Subject Next][Thread Prev][Thread Next]
- To: <seaint(--nospam--at)seaint.org>
- Subject: RE: heavy timber frames
- From: Kausik Dutta <kaushikd(--nospam--at)lntecc.com>
- Date: Fri, 3 Jul 2009 12:40:31 +0530
- Disposition-notification-to: "Kausik Dutta" <kaushikd(--nospam--at)lntecc.com>
Title: heavy timber frames
Happy Independence Day!
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.
From: Gordon Goodell [mailto:GordonGoodell(--nospam--at)harmonydesigninc.com]
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 aren’t 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 you’re talking about ability to perform into the plastic range it’s a lot about confidence, and a lot about having seen how these systems have survived real earthquakes. If you were designing the world’s 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 you’re not just talking about wood...it’s 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 you’ve 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 I’m going with R = 2”? For straw bale construction, I’ve 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.
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