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# FW: re/ Fp Values

• To: "'seaint'" <seaint(--nospam--at)seaint.org>
• Subject: FW: re/ Fp Values
• From: "La Count, Curt" <Curt.LaCount(--nospam--at)Jacobs.com>
• Date: Thu, 16 Sep 1999 09:09:00 -0700

```Rick,

Many people have been stumbling over the right seismic force to use for a
building component that spans between elevations.  The 1997 UBC is unclear,
in this case, about the proper definition of h sub x.  Outside of the Blue
Book commentary, there have been recommendations that a trapezoidal
distribution or an average of the top and bottom values be used.  In
researching this issue, I found that in the 1997 NEHRP provisions, the
variable z (same as h sub x) is defined as the highest point of attachment.

My question is; should this be the correct interpretation?  And what about
the 2 vs. 3 difference?

The answer could significantly affect design of tilt up or CMU wall panels.

TIA,

Curt La Count
Jacobs Engineering
Portland, OR

----------
From: Rick.Drake(--nospam--at)fluor.com
To: seaint(--nospam--at)seaint.org
Subject: re/ Fp Values
Date: Thursday, September 16, 1999 7:52AM

The SEAOC Design Manual, Volume 1 is determining Fp consistently with the
1997
UBC.  I am assuming you are referring to Example 36 for two-story wall
panels.
Wall panels are fastened at the top and bottom of the panel at two different
building elevations, each with its own calculated Fp value.  (Fp is a
function
of elevation within building).  When designing items fastened to the
building at
two different elevations, it is appropriate to design for the average value
calculated at the top and bottom of the panel.  Note that this "averaging"
applies to the panel only, not its connections to the building.

Hope this helps.

Rick Drake, SE
Fluor Daniel, Inc.
Aliso Viejo, CA

*****************************************************

To:   <seaint(--nospam--at)seaint.org> AT fdinet@ccMTA-fdlncta10
cc:    (bcc: Rick Drake/AV/FD/FluorCorp)

Subject:  Fp design value

there is a blue book circulating around my firm titled "seismic design
manual",
volume 1 - code application examples, by the structural engineers
association of
california.  in this manual a "new" way to calculate Fp (different than the
1997
ubc) has been shown.  i heard a rumor that i.c.b.o. had "accepted" the new
method.

here is how i see things:
Fp min = 0.7 * Ca * Ip * Wp (same as code)
Fp max = 4.0 * Ca * Ip * Wp (same as code)
Fp floor (at hx = 0) = ((Ap * Ca * Ip) / Rp) * Wp
Fp roof (at hx = hr) = Fp floor * 4
Fp design = ((larger of Fp min or Fp floor) + Fp roof) / 2
Fp design asd = Fp design / 1.4

my questions are as follows:
is this right?
do i have to design this way (since it is not in the code)?
are there other designers out there using this?