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Re: heavy timber frames

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It is an engineering judgment based on damping (energy absorption) & ductility (also related to your confidence in material values). If stick framing/plywood/nails is 6, I sure wouldn't be using 6 for adobe, haybales, heavy timber, etc.)
Chuck Utzman,P.E.

Gordon Goodell wrote:

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.

regards,

Gordon Goodell



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