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RE: Alternate load combinations

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I was asked by my boss about problems I had w/ IBC.  Below was my major
concern.  Wherever this code is adopted, it needs to be read cover to cover for
these load/resistance factor dis-harmonies.  If at all possible, we need to
adopt a single set of factors.

whoa, the room is spinning, make it stop!

Keith Fix, PE

--- "Lutz, James" <JLUTZ(--nospam--at)earthtech.com> wrote:
> I think this is a case of two codes out of step. The formula with the 1.5
> factor on earthquake loads is copied verbatim from ACI 318, which even in
> the 1999 edition still footnotes the source as ASCE 7-88. In ASCE 7-88, E is
> calculated on an allowable load basis and then factored up for use in
> ultimate strength load combinations. In the current version, ASCE 7-98, E is
> calculated on an ultimate load basis and the factor in the same formula is
> now only 1.0. It looks like an editorial lapse. When the code writers can't
> even keep track, it makes me wonder about the rest us. 
> 
> -----Original Message-----
> From: Dan Goodrich [mailto:dang(--nospam--at)karren.com]
> Sent: Thursday, February 22, 2001 12:50 PM
> To: seaint(--nospam--at)seaint.org
> Subject: Alternate load combinations
> 
> 
> UBC 1928.1.2.3 has the following load combo:
> 5.  1.2D + 1.5E + (0.5L or 0.2S)
>  
> The combo in UBC 1612.2.1 has:
>      1.2D + 1.0E + (f1L + f2S)
>  
> Is the 1.5 factor on the seismic force correct in 
> chapter 19 combo?  Why is it 50% larger?
>  
> TIA.
> Dan Goodrich, P.E.
> 


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