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Steel Knee Braced Frame & R value

Steel Knee Braced Frame & R value

Steel Knee Braced Frame & R value

Deciphering the code:
I am using RISA 3D to design a 5' high x 18' sq steel equipment platform in SDC D. I want to use a non-concentric braced framed frame system amounting to "knee braces" off the column base to the beams at 45o angle. I found that in AISC 360 C1.3a such a system is to be treated as a moment frame. I would prefer to use a OMF. Then to ASCE7-10 Ch 15.4.1 for non-building structures, it appears I have a choice to use table 12.2.1 or 15.4-1.

Using Table 12.2.1, having equipment loading < 600 psf to a edge beam and no roof, I believe I would fall in the Exception category of Section for a OMF. Then R=3.5, Ωo=3.

But looking in table 15.4-1 I find 3 options. The first line of this category list NPc,d= Not Permitted except for pipe racks < 35' or 65'. I do not have a pipe rack. So, looking down the table at the next 2 lines for the OMF is a 100' limitation and NL where R=2.5 and 1 respectively. So the way I reading this is: if I choose to use a R=2.5, I can design whatever I want as a OMF up to 100' (or the sky's the limit at R=1). Is this correct?

Does anyone see a reason I should not use R=3.5?

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