Light-framed structure above rigid structure: location of seismic base
Light-framed structure above rigid structure: location of seismic base
(OP)
If I have a multi-story light-framed structure constructed above a rigid structure (i.e. an elevated concrete slab with very stiff lateral resistance system below), could I justify considering the "base" to be the top of the elevated concrete slab for measuring the seismic height of the light-framed structure? In my opinion, the seismic response differential between these two systems makes such an assumption a more accurate analysis, but it is clearly not the conservative approach.
ASCE 7-05 section 11.2 definition of "Base":
The level at which the horizontal seismic ground motions are considered to be imparted to the structure.
ASCE 7-05 section 11.2 definition of "Base":
The level at which the horizontal seismic ground motions are considered to be imparted to the structure.






RE: Light-framed structure above rigid structure: location of seismic base
The top of a podium slab is frequently used as the seismic base in multi-family construction - wood or steel stud framing above concrete.
Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask
RE: Light-framed structure above rigid structure: location of seismic base
RE: Light-framed structure above rigid structure: location of seismic base
We found a design example at www.woodworks.org (link publications, case studies/design examples)
for a four-story wood frame structure over podium slab.
They consider the seismic base at the top of the ridgid floor.
RE: Light-framed structure above rigid structure: location of seismic base