Need a book? Engineering books recommendations...

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

RE: Seismic loads on mechanical and electrical components

[Subject Prev][Subject Next][Thread Prev][Thread Next]
The 1994 NEHRP has the same wording as ASCE 7-95, i.e. it includes
"vertically" as well as lateral/longitudinal. 

> -----Original Message-----
> From: Gunnar Hafsteinn Isleifsson [mailto:gunnarhi(--nospam--at)post4.tele.dk]
> Sent: Wednesday, December 05, 2001 6:29 PM
> To: seaint(--nospam--at)seaint.org
> Subject: RE: Seismic loads on mechanical and electrical components
> 
> 
> The design criteria is meant to be all-encompassing. I have 
> though excluded chimneys and tanks. Worst case scenario for 
> mechanical or electrical components, acc. to ASCE 7-95, table 
> 9.3.3.2,  is thus when ap/Rp equals 2.5/3.0 (stacks, 
> panelboards, etc). In my case Ca = 0.3 and Ip = 1.0, so the 
> design equation reduces to
> 
> 	Fp = ap/Rp*Ca*Ip*[1 + 3*x/h]*Wp = 0.25*[1 + 3*x/h]*Wp
> or
> 	Fp = 0.25*Wp	at grade level (using x = level of attachment)
> 	Fp = 1.0*Wp		at roof level (x = h)
> 
> This reminds me of the reason I wrote in the first place  8-)
> 
> Do any of you guys have the 1994 NEHRP Provisions (FEMA 222) 
> at hand to check if it is an error in ASCE 7-95 when it says 
> that Fp shall be applied both vertically and laterally. As 
> mentioned before; UBC94, UBC97, 1997 NEHRP (FEMA 302) and 
> 2000 NEHRP (FEMA 368) all say that Fp shall only be applied 
> horizontally.
> 
> Regards,
> Gunnar Hafsteinn Isleifsson
> Denmark
> 
> 
> -----Original Message-----
> From: Gerard Madden [mailto:gmadden(--nospam--at)duquette-eng.com]
> Sent: Thursday, December 06, 2001 01:36
> To: 'seaint(--nospam--at)seaint.org'
> Subject: RE: Seismic loads on mechanical and electrical components
> 
> 
> The 2.5 ap is for flexible equipment. Do you really have 
> that? If you are on
> springs, vibration isolators, or inertia pads then yes. Is 
> your equipment
> tall and slender and able to wobble? I would venture to guess 
> that most
> equipment is rigid if it comes pre-assembled from a manufacturer and
> contained within sheet metal walls on a base frame.
> 
> Otherwise, ap =1.0 and Fp=1/1.5*Ca*Ip*Wp=0.67CaIpWp
> 
> Otherwise, your statement is accurate.
> 
> -gerard
> SJ, CA
> 
> -----Original Message-----
> From: Gunnar Hafsteinn Isleifsson [mailto:gunnarhi(--nospam--at)post4.tele.dk]
> Sent: Wednesday, December 05, 2001 4:05 PM
> To: seaint(--nospam--at)seaint.org
> Subject: RE: Seismic loads on mechanical and electrical components
> 
> 
> I don't have the UBC97 at hand at the moment, but I seem to 
> recall that the
> worst case ratio of ap to Rp equals 2.5/1.5 which results, at 
> base level, in
> Fp = 1.67*Ca*Ip*Wp  or far higher than the minimum base 
> shear. Whether to
> use height of CG or height of attachment point would also 
> have a big impact
> on the seismic force, especially for a tall component.
> The UBC97 says that this force shall be used in LRFD or ASD load
> combinations with "rho" equal to one. I understand this so 
> that the seismic
> effects, E = rho*Eh + Ev, shall be calculated as
> 
> 	Horizontal effects:	Eh = Fp
> 	Vertical effects:		Ev = 0.5*Ca*Ip*Wp (for 
> LRFD, can be
> taken as zero in ASD)
> 
> Regards,
> Gunnar Hafsteinn Isleifsson
> Denmark
> 
> [snip]
> 
> 
> ******* ****** ******* ******** ******* ******* ******* ***
> *   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 
******* ****** ****** ****** ******* ****** ****** ********