Return to index: [Subject] [Thread] [Date] [Author]

RE: Quick/Easy Question for Seismic List

[Subject Prev][Subject Next][Thread Prev][Thread Next]
Wow!  So now I'm really confused.  I thought I understood, but now I'm
going in circles.  I'm going to have to sleep on this one overnight.

Thanks Harold,  

Mike

> -----Original Message-----
> From:	Sprague, Harold O. [SMTP:SpragueHO(--nospam--at)bv.com]
> Sent:	Thursday, March 23, 2000 1:23 PM
> To:	seaint(--nospam--at)seaint.org
> Subject:	RE: Quick/Easy Question for Seismic List
> 
> 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 >>
> > 
> 
>