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Re: Pier and grade beam foundation systems

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Try to convince the plan checker or building official that the pier and grade
beam system is not part of the "lateral-force-resisting system" (which is
defined as "that portion of the structure composed of members proportioned to
resist forces related to earthquake effects").

For residential jobs, the main purpose of the grade beam and caisson system is
to transfer the vertical dead and live loads to the ground. If there are
seismic forces resisted by this system, they are small and has only minor
contribution. 

An exception is when the system carries a significant portion of the seismic
force. Houses with steel frames or narrow shear walls with heavy uplift and
downward loads resisted by the grade beam or even if the upward and downward
forces goes diredtly to the piers, if they are heavy loads compared to the
dead and live loads, then, using one's engineer's judgement, it may be
considered as a "lateral force resisting system". 

I had a plan check correction before on a small house with a medium uplift
load on a grade beam/continuous footing. He wanted me to design the continous
footing/ grade beam per this code section but I convinced him that the seimic
related loads and stresses are small enough that  this should not be
considered as part of the lateral force resisting system. 

But it depends on how reasonable the plan checker and building official is
when it comes to city policy. In my experience, if they insist, try a
compromise where you will add more rebars or ties and increase the concrete
strength without having to go full compliance with the code section. Otherwise
you can try fighting it out agrressively and risking getting nitpicked on
other issues.

Ernie Natividad