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FW: More About 1997 UBC Fp

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Thanks for your reply Rick.

 I understand that it is not possible to write a perfect code that leaves no
room for interpretation.  Engineers should be prepared to use engineering
judgment at all times, even when the code is clear about a particular item.
I was just curious about the evolution of the F sub p topic in relation to
the h sub x issue.  If this issue was first developed in the 1997 NEHRP
provisions (from NCEER), how did the UBC depart from the intent of the NEHRP
provisions?  Or was the 1997 UBC developed first and the NEHRP provisions
based on additional research?  This applies not only to the definition of h
sub x, but also the 3 coefficient (in lieu of 2)in equation 32-2?

Curt La Count
Jacobs Engineering
Portland, OR

From: Rick.Drake(--nospam--at)
To: seaint(--nospam--at)
Subject: More About 1997 UBC Fp
Date: Thursday, September 16, 1999 11:55AM

1997 UBC Section 1632.2 clearly defines h-sub-x as the element or component
attachment elevation with respect to grade.  The key words are attachment
elevations.  These are discrete points, each with a unique value.  F-sub-p
values should not be determined at elevations that do not involve
attachments to
the structure, such as the middle of a panel.  1997 UBC Section 1632.2  goes
to specify that design lateral forces shall be distributed in proportion to
mass distribution of the element or component.

So how do we apply these requirements to panels attached at different
elevations?  The UBC is silent, allowing for engineering interpretation.
matter how conscientious, code writers just can't anticipate each and every
situation.)  However, SEAOC made certain that panels were addressed in their
Design Manual Volume 1.   The example uses an average panel design value of
F-sub-p values for each attachment elevation.  This is one rational
interpretation for this application, and one that is relatively easy to use.
Another rational engineering interpretation would be to apply a straight
(trapezoidal) distribution between the F-sub-P values.  This causes a little
more work for the engineer, and therefore, was not suggested in the Design
Manual.  I suggest that we all follow the SEAOC Design Manual Volume 1.

So how do we apply these requirements to block walls/fences?  Block walls
one attachment point, at grade.  F-sub-p values should be determined at
level only.  There is no need to complicate the problem and determine
values at the top of the wall where there are no attachments.

Hope this helps.

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