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RE: Parking Garage Loading - IBC/UBC

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Being a "wood guy", I'll admit that I don't know a lot about parking garages, however, this was a semi-controversial item in the latest round of ASCE 7 ballots.  What resulted was an entirely new commentary item that was added to ASCE 7 - 2002.  I'll not type the entire section, but will excerpt what I think is applicable.
C4.8.3 Parking Garage Loads -- Unlike live loads in office and residential buildings, which are generally spatially random, parking garage loads are due to vehicles parked in regular patterns and the garages are often full.  The rationale behind the reduction according to area for other live loads therefore does not apply.  A load survey of vehicle weights was conducted at nine commercial parking garages in four cities of different size (see reference below)..... The equivalent uniformly distributed loads (EUDL) that would produce the lifetime maximum column axial force and midspan beam bending moment are conservative estimated at 34.8 psf..... In view of the possible impacts of very heavy vehicles, however, a design load of 40 psf is recommended with no allowance for reduction according to bay area.
Wen, Y.K. and Yeo, G.L. Design live loads for passenger cars parking garages.  Journal of Structural Engineering. ASCE, 127 (3), 2001.
Since glulam isn't used much for parking garages, I didn't follow this issue as closely as some.  I don't recall if the lack of live load reduction was an issue, but from my recollection, some engineers thought that 40 psf was too low relative to the UBC required 50 psf.  Perhaps someone else who sits on ASCE 7 can fill in any details I might have missed.
Thomas D. Skaggs, Ph.D., P.E.
Senior Engineer
APA - The Engineered Wood Association
P.O. Box 11700
Tacoma, WA 98411-0700
ph: 253/565-6600
fx: 253/565-7265
-----Original Message-----
From: Jake Watson [mailto:jwatson(--nospam--at)]
Sent: Friday, April 04, 2003 7:25
To: Structural Engineering Association International
Subject: Parking Garage Loading - IBC/UBC

We are working on a precast parking garage in northern California.  The '97 UBC requires a 50 PSF live load.  This can be reduced to 30 PSF for the columns and even the double-tees we are using.  The IBC (read ASCE 7-98) doesn't allow the reduction for the double-tees and the columns will be designed for 40 PSF.  We are debating which direction to advise to owner to go.  I am not aware of any parking garage failures but don't want the building to be "under-designed" in 5 years when California does change codes to something other than the UBC.  This is a eight story garage and the impacts will be huge based on the decision.  Like usual it is a fast track job, and we need foundations in two weeks.  Opinions greatly appreciated.
Jake Watson, P.E. 
Salt Lake City, UT