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RE: Quick/Easy Question for Seismic List

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Good question.  Let me take another stab at this one. 

The ASCE 7 is referenced by the BOCA and SBC and the parent was the NEHRP.
IBC was fathered more directly by the NEHRP, but many elements of the 97 UBC
were drawn from the 1997 NEHRP.  There was a significant change from the
1994 UBC to the 1997 UBC.  Among these changes was how we calculate lateral
drift.

The 1994 UBC was indeed unitless.  Section 1628.8.2 stated to use 0.004
times the story height for short period buildings.  There is a lot of other
stuff in there that I won't go into.
(Example: period greater than 0.7 seconds, 15' flr to flr; max lat drift =
0.72 inches)

The 1997 UBC said that the delta sub M was to not exceed 0.020 times the
story height.  The units of delta sub M were not indicated.

The 1997 NEHRP uses the limit of 0.020 times h sub sx as the deflection
limit of delta sub a.  Delta sub a is listed in inches or mm.  The h sub sx
is listed in as feet or meters.
(Example: period greater than 0.7 seconds, 15' flr to flr; max lat drift =
0.30 inches)

The formulas contained in the UBC were not unit dependent in the 1994 UBC,
but they are unit dependent in the 1997 UBC.  

Shafat is correct, I just wanted to try to clarify it a bit. I hope this is
of help.

Regards,
Harold Sprague


> -----Original Message-----
> From:	Shafat Qazi [SMTP:seaint-ad(--nospam--at)seaint.org]
> Sent:	Wednesday, March 22, 2000 7:56 PM
> To:	seaint(--nospam--at)seaint.org
> Subject:	Re: Quick/Easy Question for Seismic List
> 
> Michael:
> 
> 17.76 inches is wrong. Your answer of 1.48 inches appears to be correct, 
> although little less than I am used to see. (0.166%)
> 
> The height used should be in feet not in inches. The formula uses feet.
> See 
> then definition of the story height.
> 
> Hope that helps.
> 
> Shafat
> 
> 
> 
> 
> 
> At 03/22/00 05:08 PM, you wrote:
> 
> >Is this some kind of a joke!!!  What's the difference if it is in inches
> or
> >feet.  The formula is not empirical such that changing units will affect
> the
> >value of the result.  1.48 ft is obviously equal to 17.76 inches.
> >
> >Alfonso S. Quilala Jr., P.E.
> >
> >
> >
> >
> >In a message dated 3/22/00 12:47:54 PM Pacific Standard Time,
> >mritter(--nospam--at)lgt.lg.com writes:
> >
> ><< Colleagues,
> >
> >  Please help me with a quick question.  I am looking at some calcs
> >  prepared by another engineer, who calculated the allowable story drift
> >  for a three story building from BOCA and ran the number based on story
> >  height in inches.  In other words, the building height is 74', but he
> >  used 888 inches.  This gives the allowable story drift to be
> >  0.02(888")=17.76".
> >
> >  I've always used the story height in feet, which would give an
> allowable
> >  drift of about 1.48".  I was going to show my colleage the code section
> >  which says story height is in feet, but could not find it in BOCA, UBC,
> >  SBC, Farzad Naiem, or any other text books.  Does anybody have a
> >  reference section showing that the story height, by definition, should
> >  be in feet?  I know it must be there, but I'm in a rush and can't find
> >  it.
> >
> >  Thanks again for the help!
> >
> >  Michael Ritter, PE >>
>