when to use Special Seismic Load from ASCE7-02?
when to use Special Seismic Load from ASCE7-02?
(OP)
The Special Seismic Load of 9.5.2.7.1:
Em=omegaQE +- 0.2SdsD
is to be used "where indicated" in the code...
My question is, where do you use this Special Seismic Load, Em, besides 9.5.2.6.4.2 (collectors and collector connections)?
Do I use Em anywhere else besides for collectors? I hunted through the code couldn't find anywhere else besides 9.5.2.6.4.2...
Thnaks.
Em=omegaQE +- 0.2SdsD
is to be used "where indicated" in the code...
My question is, where do you use this Special Seismic Load, Em, besides 9.5.2.6.4.2 (collectors and collector connections)?
Do I use Em anywhere else besides for collectors? I hunted through the code couldn't find anywhere else besides 9.5.2.6.4.2...
Thnaks.






RE: when to use Special Seismic Load from ASCE7-02?
in IBC 2000 a diaphram is also considered a "collector", by the way....if you know a way around this, please let me know.
RE: when to use Special Seismic Load from ASCE7-02?
RE: when to use Special Seismic Load from ASCE7-02?
RE: when to use Special Seismic Load from ASCE7-02?
rho*QE+_0.2SdsD
Maybe I'm wrong...Can you tell me where I can read about the braces needing to be designed for amplified Em? Thanks for the help.
RE: when to use Special Seismic Load from ASCE7-02?
The amplified load is not too bad, its more of a pain in the neck to track than anything. The problem that I can't get over is the req'd strength of the brace connections. I've been using SCBF to try to get around that req'ment when I have a single story bldg. Multy-story and you have to re-configure your braces or you'll end up with some monster beams due to the 13.4a req'ment.
Post back and let me know what you are able to figure out, I'm always trying to learn how to interpret these provisions.
RE: when to use Special Seismic Load from ASCE7-02?
My question is, if all members are to be designed for Amplified Em, when do you ever use regular E (rhoQe+_SdsD) in a steel structure? Never it sounds like.
ETABS uses regular E for OCBF bracing design, by the way, not Em...I emailed CSI about this, it may be a mistake in the program...
RE: when to use Special Seismic Load from ASCE7-02?
RE: when to use Special Seismic Load from ASCE7-02?
RE: when to use Special Seismic Load from ASCE7-02?
RE: when to use Special Seismic Load from ASCE7-02?
I looked at AISC.org and 341-05 takes it back out again for OCBF, so again it's E and not Em for OCBF.
Thanks.
RE: when to use Special Seismic Load from ASCE7-02?
RE: when to use Special Seismic Load from ASCE7-02?
RE: when to use Special Seismic Load from ASCE7-02?
Blake, I am using IBC03 for this OCBF. It too has that row at the bottom of table 1617.6.1 that lists systems not required seismic resistance...it references somtheing called AISC335--what is that?! Never heard of AISC335.
Thanks.
RE: when to use Special Seismic Load from ASCE7-02?
RE: when to use Special Seismic Load from ASCE7-02?
Man this is a treasure hunt...thanks for your help by the way.
RE: when to use Special Seismic Load from ASCE7-02?
RE: when to use Special Seismic Load from ASCE7-02?
D. Ordinary Concentrically Braced Frames...(14)j
Which points me to AISC 341 sect 14...but I don't understand how you know that SDC A, B, and C are exempt from 341...it seems like IBC is saying that ALL SDC's with OCBF must use sect 14 of 341...no?
RE: when to use Special Seismic Load from ASCE7-02?
Basic Structural System = Building Frame System
Basic Seismic Force Resisting System = Structural steel system not specifically detailed for seismic.
I did not mean to confuse you, but you ask when could you not design to the provisions. Confusing huh??
RE: when to use Special Seismic Load from ASCE7-02?
RE: when to use Special Seismic Load from ASCE7-02?
thanks
RE: when to use Special Seismic Load from ASCE7-02?
RE: when to use Special Seismic Load from ASCE7-02?
RE: when to use Special Seismic Load from ASCE7-02?
RE: when to use Special Seismic Load from ASCE7-02?
RE: when to use Special Seismic Load from ASCE7-02?
RE: when to use Special Seismic Load from ASCE7-02?
Em=omega*Qe+-0.2SdsD
My next question...say you are in SDC D, with an OCBF structure, where you've designed your members for Em, your column base plate connection for Em, your connections for regular E....let's look at the foundation.
ASCE 9.5.2.7 says you can neglect 0.2SdsD for fdn o'turning.
IBC 1801 says you can take 75% of your quake load for fdn o'turning.
All that being said....now, for the foundation, do you do your strength design for Em or E?
How about when you check that under service-level loads you are < qa recommended by the geotech, and check that you have no net uplift...E or Em?
Thanks!
RE: when to use Special Seismic Load from ASCE7-02?
When you say "strength design", I am assuming you're talking about reinforcing the foundation. IN MY INTERPRETATION all the omega factors and such are there to create a certain amount of pre-determined behavior/ductility in the "structural steel". With that being said, I ditch the omega for concrete design, but I've always retained Qe for overturning (i've never seen that exclusion in IBC, but I will look for it next time).
RE: when to use Special Seismic Load from ASCE7-02?
It just seems like you would include Em * 0.75 (IBC 1801) for your foundation reinforcing design, and include 0.7Em for your service-level pressure bearing check < qa.
No?