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RE: Roof Deck Personnel loading

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Your problem reminds me of when I was going to college.  High spiked heels 
were fashionable footwear for women with the bottom of the heel being about 
1/4" in diameter.  Being students with inquiring minds, and having nothing 
better to do, we tried to determine if a woman wearing high spiked heels and 
weighing about 100 lbs would be a reasonable testing apparatus for concrete, 
assuming that at some point in time her entire weight would be on the heel, 
and then again considering a 100% impact factor.  Like your problem, we 
ignored the distribution of the load.

For a simply supported 1-foot wide board or deck designed for 30 plf (i.e., 
no load distribution), the equivalent mid-span concentrated load to produce 
the same bending moment in a 4-foot span would be 60 pounds.  Or, a 200 pound 
concentrated load at mid-span would require the 1-foot wide board or deck be 
designed for 100 plf to produce the same bending moment.

BTW, high spiked heels did have an effect on the airline industry as dimples 
began appearing in aisle flooring.

Is it safe to walk on the roof?  That would depend on whether the deck was 
not connected to adjacent deck, whether it is continuous over 2 or more 
spans, whether there is load distributing insulation or fill on the deck, etc.

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

Ron Hill wrote:

. > Roger,

. > You are Correct for uniform loading.  My question is how we tell an
. > owner it is safe to walk on the roof.

. > Scenario 1:   An employee weighs 200 pounds and can easily stand with in
. > the 12" square tile on the office floor.  This computes as 200 psf.  The
. > owner asks "It is safe to walk on a 30 psf roof????"

. > Scenario 2:  The metal roof deck spans 4 ' between the joists.  A - 200
. > pound man are standing on a bay 12" wide between the joists.  Another
. > 200 pound man walks up and stands beside him to look at the AC unit.
. > Their weight on the deck bay is now 400/1/4 = 100 psf.  The combinations
. > are endless.

. > I have not seen any information in SDI that can document that the
. > loading is safe.

. > Ronald A. Hill, P.E.

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