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RE: 1.2 stress increase

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There also used to be a provision (at least in the 2001 CBC) that allowed phi to be taken as 1 when using special seismic load combos (omega) in LRFD design.  Does that still exist?  Maybe it was never in the ASCE 7.

 

Thanks,

 

Doug Mayer, SE

Structural Engineer

 

From: Yousefi, Ben [mailto:Ben.Yousefi(--nospam--at)mountainview.gov]
Sent: Monday, November 17, 2008 12:03 PM
To: seaint(--nospam--at)seaint.org
Subject: RE: 1.2 stress increase

 

The only factor that is not allowed for steel is the old 1.33 increase for short term wind and earthquake loading. The 1.2 factor is needed when using ASD load combination including Omega factor since we have eliminated the old 1.7 factor (UBC). We now use 0.7OQE in the ASD load combination, therefore the 1.2 is to provide equivalence to the old 1.7 factor [(1/0.7) (1.2) =1.7]

 

Ben Yousefi, SE, CBO
Chief Building Official
City of Mountain View, CA
(650) 526-7007
ben.yousefi(--nospam--at)mountainview.gov


From: Mark D. Baker [mailto:shake4bake(--nospam--at)verizon.net]
Sent: Sunday, November 16, 2008 9:34 PM
To: seaint(--nospam--at)seaint.org
Subject: 1.2 stress increase

 

Per ASCE 7-05, when using equations with overstrength factor (ASD), section 12.4.3.3 allows a 1.2 stress increase. I can’t find anywhere in the code where this increase is disallowed for steel, including AISC 341.

 

For some reason it is floating around in my brain that the 1.2 incr is not allowed for steel….am I imagining this?

 

Regards,

 

Mark D. Baker

Baker Engineering