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Re: parking sttructure live load

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It seems that these loads (2000 lb point load; 50 psf distributed 
with some reduction allowed) have traditionally worked well in U.S. 
design.  I thought now would be a good time to raise a point that 
will affect garage designs fairly soon.

The 2000 IBC will say, "The live loads shall not be reduced in 
passenger car garages except the live loads for members supporting two
or more floors are permitted to be reduced by a maximum of 20% but the
live load shall not be less than L as calculated above."

"L calculated above" is using the normal tributary area live load

This is a significant departure from practice under the UBC which
allowed live load reduction by up to 40%.  In particular, we won't be
able to reduce live loads for beam design at all (design for 50 psf,
not 30 psf) and the allowed reduction for columns and transfer girders
is smaller (20% not 40%).

This change is to be consistent with ASCE 7, which has traditionally
not allowed LL reduction in parking garages.  Not everyone on ASCE 7 
believes that LL reduction is inappropriate for parking garages.  
However, it will take years to change ASCE 7 and noone challenged 
this provision in the IBC process.  It looks like garage design in 
the U.S. will change (at least for a few years).


> Date:          Fri, 13 Aug 1999 19:42:39 -0400
> From:          Roger Turk <73527.1356(--nospam--at)>
> Subject:       parking sttructure live load

> Actually, the 50 psf can reduce to about 35 psf considering reduction for 
> tributary area.  But you also have the 2,000 lb concentrated loads (1604.3, 
> 1994 UBC) to consider.

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Michael Valley                                   E-mail: mtv(--nospam--at)
Skilling Ward Magnusson Barkshire Inc.                  Tel:(206)292-1200
1301 Fifth Ave, #3200,  Seattle  WA 98101-2699          Fax:        -1201