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RE: UBC: How Do You Interpret 1997 UBC P

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Bill,

The live load reduction rationale is based on the assumption that as
tributary area increases, the likelihood of the entire area being loaded the
specified amount diminishes.

For example, a 50 psf LL is the equivalent of 200 pound men at 2-feet on
center over the entire area.  While this could possibly occur in an area of
10 sq. ft., the likelihood that you would have this occurrence at areas
greater
than 150 sq. ft. is remote.  Note that your LL reduction does not kick in
until the tributary area is greater than 150 sq. ft.  Maximum LL reduction is
40 percent.

A typical parking space for private passenger cars is 8' X 20' (160 sq.
ft.).  At a loading of 30 psf (40% reduction), we would be looking at a
4800# car; at 50 psf (no reduction), we would be looking at an 8000# car,
in addition to having all the aisles similarly jammed with cars.   What is a
conservative weight for a passenger car: 4000#, 5000#, 6000#?

BTW, does the lawyer want you to determine the cause of the problem(s) or is
he/she focusing on the LL reduction.  If the latter, the attorney is looking
for a whore on whose testimony the attorney can base his/her case.

A. Roger Turk, P.E.(Structural)
Tucson, Arizona

Bill Polhemus wrote:

. > Now comes my ignorant question:

. > Other than due to tributary area, is there any other rationale for
. > reduction of the live load?

. > (The reason for my ignorance is that I have never used a reduction for
. > live load. I'm just a bit conservative that way, I suppose. Partly this
. > has to do with my training on Wal-Marts, where due to some specific past
. > problems of roof structural failure we did not reduce live load for any
. > reason. But now I'm having to examine the calculations of the EOR where
. > he DID use the LL Reduction).

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