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FW: Pier and grade beam foundation systems

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IMHO, the pier and grade beam system is part of the lateral system unless
there is a Substantially  more rigid load path for seismic forces (passive
earth pressure).  If the piers and grade beams are part of the lateral
system, they are subject to the provisions of UBC  1921.  The requirements
of 1921 may be avoided only if the design basis for seismic forces is not
relying on "energy dissipation in the non linear range of response"
(1921.2.1.1).  This would mean that the special detailing provisions of UBC
1921 are not required if the design forces are derived with an Rw=1.  I
would use this exception with caution, depending on your location and the
possible consequences of larger than calculated forces.

I hope that this helps.

Curt La Count, P.E.
Jacobs Engineering Group
Portland, OR
From: John Buchanan
To: seaoc(--nospam--at)
Subject: Pier and grade beam foundation systems
Date: Tuesday, April 07, 1998 4:41PM

To all:

I have a general question regarding a foundation system for residential
wood structures founded on a pier and grade beam foundation system.

A college of mine has received a plan check comment from a locale building
official stating that the pier and grade beam system should be considered a
reinforced concrete frame structure and designed per the requirements of
section 1921 of the 1994 Uniform Building Code.

The standard of care for the area has always been to use an 8" x 18" or 24"
deep concrete grade beam with #3 ties and 2 #5 bars top and bottom. The
beam reinforcing varies per the vertical load. Typically the piers are
spaced at eight to twelve feet on center.

The grade beams are tied to the piers with four #5 bars from the grade beam
to the top of the pier.

The piers are reinforced with six number five bars and #3 ties at 10" o.c.
with 4 #3 ties at two inches o.c. at the top of the pier.

So the question is should the pier and grade beam system be considered a
frame system a be detailed per the requirements of chapter 21?

If the consensus is no, how does one confront the building official? (There
is a board of appeals)

My college has called the ICBO and they do not offer any help.
Calls to ACI have been relatively unresponsive and they try to defer the
question to others.
(makes you want to be a member Ha!!!!)

Have a call into EERI to discuss the project but no return phone calls as
of yet.

So does any one have any comments?\

John Buchanan