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Re: Question on need to use "skip" live loads in 2-way slabs

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I don't believe this posted on my first send attempt...
 
That would be my guess as well.  I think there may be some restriction to it, along the lines that no span can be less than 1/3 or ½ of an adjacent span, so uplift is not an issue?  Perhaps this is addressed with the 75% factor.  I haven't performed calculations seeking the LL limit, but I have noticed when the DL is significant, the alternating load conditions appear much less frequently.

>>> smaxwell(--nospam--at)engin.umich.edu 10/23/02 11:42PM >>>
Cliff,

I _might_ know why, but haven't done the math to prove it.  Sit down and
do some calculations.  Do one continuous beam analysis with DL and
LL<=75%DL on each span.  Then do one continuous beam analysis with DL on
each span and LL<=75%DL on every other span.  Then do some other
combinations of LL patterns if you want.  My guess is that none of the
cases with LL patterns will create larger maximum moments or shears than
the case with LL on every span.  In otherwords, my guess is that when the
LL is 75% or less of the DL, it becomes impossible for the "skip" patterns
to "beat out" the case with LL on every span.  Thus, there would be no
reason to even spend the time analyzing the various cases since they will
not govern.

Since I have not sat down and proven this to myself with some
calculations, I could be wrong.

HTH,

Scott
Ypsilanti, MI