Verifying, when R = 3 or less AISC SP doesn't apply?
Verifying, when R = 3 or less AISC SP doesn't apply?
(OP)
Hello,
Just wanted to verify with someone, I designed a structure with R=3 for seismic base shear. Does that mean I do not need to follow AISC seismic provisions? I overheard from someone in this forum where they mentioned if R=3 or less AISC SP doesn't apply. Where is this noted specifically?
Thanks!!
Jeff
Just wanted to verify with someone, I designed a structure with R=3 for seismic base shear. Does that mean I do not need to follow AISC seismic provisions? I overheard from someone in this forum where they mentioned if R=3 or less AISC SP doesn't apply. Where is this noted specifically?
Thanks!!
Jeff






RE: Verifying, when R = 3 or less AISC SP doesn't apply?
This is stated in AISC 341 in Section 2.1.
"When the seismic response modification coefficient, R, is taken as 3 or less, the structure is not required to satisfy these Provisions, unless specifically required by the applicable building code"
RE: Verifying, when R = 3 or less AISC SP doesn't apply?
RE: Verifying, when R = 3 or less AISC SP doesn't apply?
Can I justify by using R=3 due to ASCE 7-05 that the structure is not specific braced frame?
RE: Verifying, when R = 3 or less AISC SP doesn't apply?
Also note -- a knee braced frame is not a brace frame, it is a moment frame, and can be detailed according to the ordinary moment frame provisions if you are in a higher seismic design category.
RE: Verifying, when R = 3 or less AISC SP doesn't apply?
The platform is for recycling plants. These recycling plants can be located anywhere in the world...
I've classified them under occupancy category I. I guess I can tell my boss that this platform is to be only located in areas with SDC =A,B, or C ??
RE: Verifying, when R = 3 or less AISC SP doesn't apply?
RE: Verifying, when R = 3 or less AISC SP doesn't apply?
by using R=1, what is this assuming about the response of the structure...I thought the seismic loads/response were capacity driven...
RE: Verifying, when R = 3 or less AISC SP doesn't apply?
By using an R=1 you are assuming the structure remains elastic. So under the design earthquake nothing should yield.
RE: Verifying, when R = 3 or less AISC SP doesn't apply?
RE: Verifying, when R = 3 or less AISC SP doesn't apply?
Therefore my R=3.5 per ASCE 7-05 chapter 12.
The thing is, I'm using a conservative base shear of .4W regardless of the formula provided in ASCE 7-05. It was a conservative approach based on a Seismic Zones Map of the United States provided by my company.
The problems I'm running into now is... I'm using W shapes for my columns and since I decided to go with knee braces in both directions, I'm going to have larger columns to satisfy combined moment(both x and y directions) and axial load. I might be forced to go with a CBF in the weaker directions.
RE: Verifying, when R = 3 or less AISC SP doesn't apply?
RE: Verifying, when R = 3 or less AISC SP doesn't apply?