Need a book? Engineering books recommendations...

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

RE: Formula for Fp with Braces

[Subject Prev][Subject Next][Thread Prev][Thread Next]
Bill,

I think your way of reading it is correct.  It is permissible to apply different values of Fp to shallow anchors than to other components.  Very helpful.  

Thanks,
MJ

"Sherman, William" <ShermanWC(--nospam--at)cdm.com> wrote:

>My interpretation is that the reduced Rp value of 1.5 only applies to
>the "anchorage", not to the whole system.  See also footnote 14 to Table
>16-0; for this similar situation "the design forces for the anchors" are
>increased by a factor of 2.0, not for the whole mounting frame.
>
>William C. Sherman, PE
>(Bill Sherman)
>CDM, Denver, CO
>Phone: 303-298-1311
>Fax: 303-293-8236
>email: shermanwc(--nospam--at)cdm.com
>
>
>> -----Original Message-----
>> From: Markajohn(--nospam--at)cs.com [mailto:Markajohn(--nospam--at)cs.com]
>> Sent: Tuesday, July 05, 2005 8:28 PM
>> To: seaint(--nospam--at)seaint.org
>> Subject: Formula for Fp with Braces
>>
>> Hello fellow Engineers:
>>
>> Here is an issue that I think will come up for me soon.  I
>> was recently involved in designing seismic bracing for some
>> process pipe runs.  The pipes are supported on trapezes
>> (all-thread hangers and a unistrut cross member) hung from
>> the underside of a concrete slab.  On about every other
>> trapeze, there would be a 45 degree kicker running up from
>> the cross member to the underside of the slab and attached
>> there with a shallow (less than eight diameters) expansion bolt.
>>
>> Section 1632.2 of the 1997 UBC gives a formula for Fp and a
>> requirement that Rp is 1.5 for shallow expansion anchors.  Rp
>> is usually 3.0, so this requirement has the effect of
>> doubling the Fp.
>>
>> So my non-engineer client will say, "no problem, just double
>> up on the number of expansion bolts at the top of the brace.
>> But this doubles the force on the rest of the brace too
>> including the hanger rod and its' attachment to the underside
>> of the slab which then needs to be increased.
>>
>> I know some engineers use the doubled Fp to design only the
>> shallow anchor attachment at the top of the brace but just
>> use the reduced Fp (as if Rp were 3.0 instead of 1.5) to
>> design the rest of the brace.
>>
>> I know this is not per the code, but what's wrong with it?  I
>> wouldn't want my client to call me a code monkey.
>>
>> The answer will have a legal aspect to it as well as an
>> engineering aspect.
>>
>> TIA
>> MJ
>
>******* ****** ******* ******** ******* ******* ******* ***
>*   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 
******* ****** ****** ****** ******* ****** ****** ********