huangyhg

caisson structural slab w/out interior grade beams
at typical caisson foundation systems is necessary to provide a cap with grade beams framing into two directions similar to a pile fdn system? i'm trying to save money for a project and would like to design my foundation system like an elevated structural slab over concrete columns thus eliminating interior grade beams. i would then add column drops as required for punching shear and design the slab as a flat plate. what are everyone's thoughts?
tia
i don't have a copy of the ibc 2000 or ibc 2003 in front of me but in section 18. the grade beams can be omitted as long as you are in a seismic b or higher (please confirm).
if not, there are a few requirements that you have to meet based on your axial load in your column.
i would carefully read section 18 of the code to see exactly what are the requirements.
wish i could give you the section.
hope this helps
i think what you are doing can work. usually, though, you'd still consider grade beams around the perimeter of the building to add stiffness and to minimize reinforcing steel for the edge condition, especially if you are supporting a heavier exterior wall.
the chapter 18 issues that struct59 refers to deals with the requirement in higher seismic areas to laterally tie the tops of piers/piline together with grade beams. this is in cases where columns come down to the first (ground) floor and are directly supported by piers/piles. in your case, your whole floor system would serve that purpose, eliminating the concern that the tops of the piers (bottom of the columms) would spread laterally in a seismic event.

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