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Re: Parking Garage Loading - IBC/UBC

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This is my opinion on parking garage loading (taken from something I wrote):

While most building codes and standards specify a live load of 50 psf for parking structures, permissible live load reductions vary widely. The IBC, the BOCA National Building Code, and the ASCE 7 Standard do not allow live load reduction for horizontal members but allow a 20% live load reduction for columns supporting two or more floors.  The Uniform Building Code (UBC) allows a maximum 40% reduction for both horizontal members and columns.  The Standard Building Code (SBC) allows a maximum of 40% reduction for horizontal members and 60% for columns.

The use of live load reduction in parking garages is typically justified because actual automobile weight in a fully loaded parking garage will seldom exceed 25 to 30 psf.  A nominal added reserve capacity may be desirable to account for future dead loads such as overlays, however.


The critical stage for collapse is probably during construction.  The precast parking garage that collapsed in Maryland last fall was an 8-story garage.  I heard (from someone "close to the investigation") that there may have been a problem with how many levels they had erected without having welded the flanges.  Eight stories is actually somewhat tall for a parking garage - owners have figured out that the top stories never get used, because people don't want to drive up a mile of ramps to find a parking space.  In the garage in Maryland,   the erectors may only previously have done three or four story garages,  and thus not had a problem with leaving flanges up welded.

Gail Kelley