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Re: UBC: How Do You Interpret 1997 UBC P

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It seems that if you use a reducible 50 psf loading, or a non-reducible 40
psf loading, you end up with the design live loading in the same neighborhood.

I should probably have elaborated in the example that I gave that neither the
design loading, nor the fact that tour buses had been parked on the deck
were, IMO, the cause of the distress that I observed.  The distress was
severe spalling of concrete on support columns and started occurring within 6
months after completion of the structure.

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

Gil Brock wrote:

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Maybe the low loads you get after reductions is the reason why many codes
(not including ACI) do not allow live load  reductions based on tributary
area for parking garages along with places of assembly, vaults, strongrooms

At 10:40 PM 5/03/02 -0500, you wrote:
>Reductions based on tributary area will frequently reduce the 50 psf load in
>parking structures to 30 - 35 psf.  If we have a 4,000 pound car and assume
>that it occupies a space of 6' X 20', its weight is equivalent to 33 psf over
>that same area.  Concentrated load from each wheel would be 1,000 pounds each
>(compare that to the concentrated load that the code requires --- I don't
>have my '97 UBC handy).  So even if we had every parking space filled, and
>cars lined up to leave the parking deck, it seems that the 50 psf (reduced)
>would still be a realistic loading.
>Is there a fixed barrier that will prevent use of the parking deck by trucks,
>buses, motor homes, etc?  If not, is there some other positive barrier that
>would prevent their access to the parking deck?  Is the fire department going
>to use the deck to fight fires?
>Just as you and I cannot predict what state-of-the-art report is going to be
>written in 5, 10, 15, or so years, we cannot use a current state-of-the-art
>report to indict a design done in the past.
>In a report that I did on distress in a 2-level parking structure that was
>built into the side of a hill so that access to the upper level was directly
>from a road on the hill, I stated that the engineer used the appropriate code
>required loading for private passenger cars, but some barrier should be
>installed to keep trucks from accidently entering the parking deck.  The
>owner's face turned ashen as he stated that they had used the deck to park
>tour buses.  Shortly thereafter portals were constructed at the entrance to
>the upper level (and at about three other parking structures that I am aware
>A. Roger Turk, P.E.(Structural)
>Tucson, Arizona
>Bill Polhemus wrote:
>. > This came up in a discussion with an attorney today.
>. > The referenced paragraph states:
>. > "Live loads shall be the maximum loads expected by the intended use or
>. > occupancy but in no case shall be less than the loads required by this
>. > section."
>. > Now, in the case that I'm consulting on, the EOR has repeatedly denied
>. > responsibility from problems with a parking deck structure based on the
>. > fact that "they used the loads prescribed by the building code."
>. > However, one line of inquiry has been that the loads applied by
>. > "pleasure-type vehicles" possibly exceed those prescribed in 1997 UBC
>. > Table 16-A and in 1607.3.3 "Concentrated Loads".
>. > This leads to two questions that I'd like to be able to answer succinctly
>. > for my client the shyster:
>. > 1) How does one determine if "the maximum loads expected by the use"
>. > exceed and should take the place of "loads required by this Section [i.e.
>. > UBC Section 1607 "Live Loads"]?
>. > 2) Assuming that such a determination must be made, how have such loads
>. > been arrived at?
>. > Regarding the second question in particular I have noticed that ASCE
>. > publishes a "Design Live Loads for Parking Garages." I have ordered this
>. > publication, but in the meantime the abstract published on the ASCE
>. > website mentions that the publication (which appears to be a monograph)
>. > concludes that the 50 psf prescribed in UBC could rationally be reduced
>. > about 40 psf, but that in many (most?) cases the standard reductions
>. > allowed by the Code should not be taken. Anyone have any comments on

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