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RE: Steel strsss increase for seismic loads

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According to Breyers section 2.17, stress increase is not allowed for wood.
Duration of load Cd for ASD and time effect factor lambda for LFRD are
applied as modifications, but might be allowable per IBC ASD alternate load
combinations.

-----Original Message-----
From: Drew Morris [mailto:dmorris(--nospam--at)bbfm.com] 
Sent: Tuesday, April 21, 2009 3:05 PM
To: seaint(--nospam--at)seaint.org
Subject: Re: Steel strsss increase for seismic loads

I believe wood uses the duration factor Cd so it can vary from 0.9 to 1.6.

Larry Hauer wrote:
> Thanks Tom, that is what I thought with WOOD and masonry the only 
> materials being allowed the 1/3 increase. (Oh well!).
>  
> Larry
>  
> ----------------------------------------------------------------------
> --
> To: seaint(--nospam--at)seaint.org
> Subject: Re: Steel strsss increase for seismic loads
> From: Tom.Hunt(--nospam--at)fluor.com
> Date: Tue, 21 Apr 2009 14:22:48 -0700
>
>
> Larry,
>
> If you use the load combinations from IBC Section 1605.3.1 then a 1/3 
> increase in allowable stresses is not permitted.  If you use the IBC 
> load combinations from Section 1605.3.2 then you are allowed to use 
> the 1/3 increases *but ONLY if allowed by the material chapter*.
>  Unfortunately for steel neither the IBC nor AISC have the 1/3 
> increase factor anymore.  I believe the only material left is masonry 
> and in some cases geotechnical soil bearing.
>
> Thomas Hunt, S.E.
> Fluor
>
>
>
>
>
> 	*Larry Hauer <lhauer(--nospam--at)live.com>*
> 04/21/2009 02:09 PM
> Please respond to seaint 	
> To
> 	"Struct. Eng. Assoc." <seaint(--nospam--at)seaint.org> cc
> 	
> Subject
> 	Steel strsss increase for seismic loads
>
>
>
> 	
>
>
>
>
>
> I am checking existing steel roof framing members for support of 
> replaced roof top mechanical equipment. Obviously, I need to design 
> per the '06 IBC/'07 CBC for seismic forces and will be using ASD 
> equation 16-20 of the IBC/CBC. Based on Sec. 1605.3.1.1 it looks like 
> a 1/3 increase in allowable stresses for the existing steel roof 
> members is no longer allowed when considering seismic loads. Is this 
> correct?
>
> Thanks in advance,
>
> Larry Hauer
>
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