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# RE: re/ Fp Values

• To: <seaint(--nospam--at)seaint.org>
• Subject: RE: re/ Fp Values
• From: "Bill Allen" <Bill(--nospam--at)AllenDesigns.com>
• Date: Thu, 16 Sep 1999 10:52:09 -0700

```To me, this is a valid question (since I KNOW there are several folks out
there applying a pseudo trapezoidal shaped load to a wall) in addition to
the following one:

Why isn't this more clear in the code?

As far as free standing block fences over 6 ft. high (I guess there are no
design values for walls less than 6 ft. high), Table 16-O gives values for
a-sub-p and R-sup-p. Of course, where it gets confusing is applying these
values into Eqn 32-2 since there is no h-sub-r. From previous comments on
this list, I have been instructed to set the h-sub-x over h-sub-r term to
zero, but this method is not that clear. What would folks do if they aren't

Why isn't this more clear in the code?

I know this is 20/20 hindsight, but it appears to me that (IMO):

1. The design manuals should have come out before the 1997 UBC took effect
and
2. There should have been provisions for intermediate issues of the building
code as there were in previous editions.

Getting a little ahead of myself, I recently got into an argument with a
plan checker with regards to the design and detailing of openings in shear
walls (see Fig 23-II-1). After twenty something years of structural
engineering, I thought I knew how to do this. Not according to the plan
checker. For the horizontal check/connection, I calculated the drag force
based on the shear above the opening and the shear below the opening. I
provided blocking and strapping to accommodate this drag force. For the
vertical component (continuous framing member-king stud), I calculated the
axial force by multiplying the shear force in the pier by the pier height
and dividing by the pier width. This is like: T=C=M/d. I divided this force
by the distance from the top of the pier to the top plate to give a distance
in which this "chord force" could be transferred into the panel above the
pier. I then provided boundary nailing that would transfer this force. As
shocking as this may seem, the plan checker did not think that this was an
adequate "Design for force transfer ... based on a rational analysis" (see
2315.1, 5th paragraph). Sheesh. At this point in my career, I no longer am
interested in getting into a debate with the plan checker. I just want to
finish the job and move on to the next one. It would have been nice to have
an example (such as one that may be included in an upcoming design
manual???) to reference.

And, finally, whatever happened at that infamous Seismology committee
meeting held on August 13th?

Bill Allen, S.E.
ALLEN DESIGNS
Laguna Niguel, CA

|| -----Original Message-----
|| From: La Count, Curt [mailto:Curt.LaCount(--nospam--at)Jacobs.com]
|| Sent: Thursday, September 16, 1999 9:09 AM
|| To: 'seaint'
|| Subject: FW: re/ Fp Values
||
||
|| 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?
|| 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
||
|| *****************************************************
||
||
||
||
||
|| 06:42 AM EDT
||
|| 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?