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Re: AISC Seismic for ASD

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Section 4.1 gives the load combinations, which are similar to the LRFD load combos. So, in essence your load calculation and resistance is done similar to LRFD method, you just use the ASD provisions to get the allowable stresses. To be honest with you though, I have yet to see anyone do it this way. Most engineers are still plowing away the old fashioned way, and as far as I know most plan check engineers don't seem to mind either, since the end results is essentially the same.

>>> HoodMO(--nospam--at)ci.anchorage.ak.us 12/05/03 01:23PM >>>
Seaint,

I have a question about the ASD alternative (Part III) of the 1997 AISC
seismic provisions. Section 4.2 allows the nominal strength of a member
to be calculated by multiplying the allowable stresses by 1.7. According
to section 4.3 the design strength is calculated my multiplying this
nominal strength by the appropriate Resistance Factor.

Ok, so now I've got the design strength of my member. To me this
indicates I should be comparing the values calculated to the required
strength (LRFD) load combinations of the building code, in my case the
2000 IBC. 

My question is: where is this called for in the code? I'm using the
allowable stress alternative in the seismic provisions so could I
actually use the ASD load combinations (divide E by 1.4)!? This doesn't
seem right to me, but I can't figure out why it's wrong. Any thoughts?

Thanks,
Matthew O. Hood, E.I.T.
Anchorage, AK

 

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