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RE: UBC: How Do You Interpret 1997 UBC P

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"What is a conservative weight for a passenger car: 4000#, 5000#, 6000#?"

Courtesy of the Chevy web site, a Cavalier (subcompact) weighs approximately
2,617#.  Based on an 8'x20' parking space, that is 16 PSF.   A Suburban (big
SUV) weighs approximately 5,700#.  Based on the Suburban's dimensions of
219.3"x79.8", it is 46.7 PSF on the area immediately under it and only 36
PSF on an 8'x20' parking space.  Chevy lists the maximum fully loaded weight
of the Suburban as 8,600#.  This is 70 PSF on the area immediately under the
truck itself, but only 53 PSF on the 8'x20' parking space.  Although many
people believe that large SUVs exceed parking structure design loads, this
can only happen if the SUVs are heavily loaded, and even then the overload
only exists on a very localized basis.  The 50 PSF code load roughly
accounts for a parking garage full of Suburbans parked tight against one
another (no space even to open doors) and filling the drive aisles and every
other nook and cranny of the floor.  The Ford Expedition, their largest SUV,
is approximately the same size and weight as the Suburban.  Given that this
wildly unlikely scenario is what it takes to get to 50 PSF, I feel very
comfortable with that design load for typical parking garages where large
truck loads are prevented.  I think that the same line of reasoning could be
used to allow LL Reduction (as is done in the UBC) for parking structures.
Not knowing the specifics of Bill's project, it is hard to say for sure, but
50 PSF is generally fine.  I would hope that they have explored other
issues, such as whether the building design is adequate for 50 PSF and
whether it was constructed properly, before assuming 50 PSF is the problem
(again, assuming typical garage loads, and not a UPS depot or something
unusual like that).

Paul Crocker, P.E.

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