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Re: Pier and grade beam foundation systems

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Rhkratzse wrote:

> In a message dated 4/7/98 5:36:33 PM, John Buchanan wrote:
> <<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.
> >>
> Do (vertical and lateral) loads, downslope soil pressure, soil capacity,
> seismic ductility, etc., have any place in this, or it is all just a concrete
> version of "Conventional Construction" provisions that aren't engineered, just
> followed--like a cookbook?

Good point here Ralph. Sometimes questions like these force us to consider what we
are doing.

Further thinking about whether the pier and grade beam system has an option to
behave as part of the lateral system brings me back to the realization that not
only is it a part, but the primary deliverer of such forces. I am often trapped in
my thinking that these originate in the weights of the superstructure and forget
that the origin comes from it's gravity load system. Which brings me to emphasize
the connection between the pier tops and grade beams.

As another consideration, if the piers are anchored some distance below grade,
isn't the structural model for the building frame for earthquake considerations
more like the inverted pendulum? This would perhaps "penalize" the delivering
system, but at the same time could be considered an absorbing or ductile-like
element. Any comments??

Barry H. Welliver
Draper, UT