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Re: asd vs lrfd

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Perhaps this line of reasoning should be considered:  Load factors are used
to predict what might happen under "ultimate" loads, not service loads.
When the ultimate loading occurs, the point of zero soil pressure WON'T 
be in the same place as it is under service loads!

Joe McCormick

At 07:33 PM 10/13/97 -0400, you wrote:
>>Are you considering both load cases per ACI 318 Section 9.2.2 (i.e. a
>>dead load with wind or earthquake)?  I am surprised that uplift
>>disappears if 
>>both load cases are considered. 
>This has occured to me so often with eccentrically loaded footings
>under just DL and LL loads and with retaining walls, all not subject
>to wind or earthquake loads, that I now expect this to happen.  My
>*solution* to the problem has been to hold the point of zero soil
>pressure as determined from service loads and apply the load factors
>to the soil pressures from DL and LL at the point of maximum combined
>service load pressure. 
>The only additional thing that I can say is, check it out the next
>time that you have an eccentrically loaded footing that has partial
>uplift under dead and live service loads.  Of course, if you use a
>computer program, you can't *see* what is happening and the computer
>program is incapable of thinking about what is happening.
>A. Roger Turk, P.E.(Structural)
>Tucson, Arizona