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RE: IBC Sec. 1617.1
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- Subject: RE: IBC Sec. 1617.1
- From: Scott Maxwell <smaxwell(--nospam--at)engin.umich.edu>
- Date: Fri, 12 Sep 2003 15:29:32 -0400 (EDT)
Brian, I thought that the 1997 NEHRP would provide clear guidance on it...was just too lazy to dig it out and really look. ;-) Regards, Scott Ypsilanti, MI On Fri, 12 Sep 2003, Brian Harris wrote: > Scott and Jason- > > The 1997 NEHRP commentary makes it clear that this is a vertical effect: > > "In Eq. 5.2.7-1 and 5.2.7-2 , a factor of 0.2SDS was placed on the dead load to account for the effects of vertical acceleration." > > These two equations are labeled as 16-28 and 16-29 respectively in the 2000 IBC. > > -Brian Harris > > -----Original Message----- > From: Scott Maxwell [mailto:smaxwell(--nospam--at)engin.umich.edu] > Sent: Friday, September 12, 2003 11:23 AM > To: seaint(--nospam--at)seaint.org > Subject: Re: IBC Sec. 1617.1 > > > Jason: > > To me, the definition of E just after Equation 16-28 should help provide > some clarification. > > It states: > > "E = The combined effect of horizontal and VERTICAL earthquake-induced > forces." (emphasis is mine) > > Add to that, that QsubE is defined as: > > "QsubE = The effect of horizontal seismic forces." > > To me, that makes the 0.2SsubDS*D term a vertical component term. > > Further more, this is consistant with how the 1997 UBC deals with the > similar situation (and the 1997 UBC is to some degree at least a minimal > basis for what is in the 2000 IBC). The similar equation in the UBC (eq > 30-1) is E = rho*Eh + Ev. And Ev is clearly defined as the vertical > component of the earthquake ground motion ("Ev = the load effect resulting > from the vertical component of the earthquake ground motion and is equal > to an addition of 0.5*Ca*I*D to the dead load effect, D, for Strength > Design, and may be taken as zero for Allowable Stress Design.") > > And last, since the 2000 IBC Seismic provisions are basically based off of > the NEHRP Provisions, you could get a hold of the 1997 NEHRP provision and > see what the commentary says on this section. > > HTH, > > Scott > Ypsilanti, MI > > > On Fri, 12 Sep 2003, Jason Kilgore wrote: > > > I normally work with buildings with a seismic design category of A, B, or C, > > so I rarely use Equations 16-28 through 16-31. (rho = 1, I don't use > > section 1617.1.2, and 0.2*Sds = about 0.02). > > > > Now I've got a problem with an Sds of 68%, so the second term in those > > equations is much higher. > > > > It's obvious that the first term acts horizontaly (Qe). I've always worked > > on the assumption that the second term acts vertically. For example, take a > > drag strut with vertical and horiz. loads. Assume rho = 1.5. > > > > E = rho*Qe +/- 0.2*Sds*D > > E = 1.5*Qe +/- 0.136*D > > > > You would then plug this value of E into, for example, Eq. 16-5: > > F = 1.2*D + 1*E + 0.5*L + 0.2*S > > > > F = 1.2*D + 1.5*Qe + 0.136*D + 0.5*L + 0.2*S > > > > F = 1.336*D + 1.5*Qe + 0.5*L + 0.2*S > > > > In other words, the "D" value from equations 16-28 through 16-31 are added > > to the "D" in whichever final load equation you use. > > > > Recently it was pointed out to me that the D in those equations is actualy a > > horizontal force, and should be directly added to Qe to get a purely > > horizontal "E" force. In other words, part of the horizontal load in a > > member is from the seismic base shear, and part is caused directly by the > > dead weight (and supported dead weight) of the member itself. > > > > I think this person is wrong, but would like other expert opinions. > > Thanks, > > > > ---- > > Jason Kilgore > > Leigh & O'Kane, L.L.C. > > > > > ******* ****** ******* ******** ******* ******* ******* *** > * Read list FAQ at: http://www.seaint.org/list_FAQ.asp > * > * This email was sent to you via Structural Engineers > * Association of Southern California (SEAOSC) server. To > * subscribe (no fee) or UnSubscribe, please go to: > * > * http://www.seaint.org/sealist1.asp > * > * Questions to seaint-ad(--nospam--at)seaint.org. Remember, any email you > * send to the list is public domain and may be re-posted > * without your permission. Make sure you visit our web > * site at: http://www.seaint.org > ******* ****** ****** ****** ******* ****** ****** ******** > > ******* ****** ******* ******** ******* ******* ******* *** > * Read list FAQ at: http://www.seaint.org/list_FAQ.asp > * > * This email was sent to you via Structural Engineers > * Association of Southern California (SEAOSC) server. To > * subscribe (no fee) or UnSubscribe, please go to: > * > * http://www.seaint.org/sealist1.asp > * > * Questions to seaint-ad(--nospam--at)seaint.org. Remember, any email you > * send to the list is public domain and may be re-posted > * without your permission. Make sure you visit our web > * site at: http://www.seaint.org > ******* ****** ****** ****** ******* ****** ****** ******** > > ******* ****** ******* ******** ******* ******* ******* *** * Read list FAQ at: http://www.seaint.org/list_FAQ.asp * * This email was sent to you via Structural Engineers * Association of Southern California (SEAOSC) server. 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- RE: IBC Sec. 1617.1
- From: Brian Harris
- RE: IBC Sec. 1617.1
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