implied linear foot structural problem (ballast practice CS5 7)
i'm trying to work a couple structural problems. question and answer posted below.
dead load = 15#/ft
live load = 40#/ft
total load = 55#/ft
beams are the items labeled B over the footings. joists span perpendicularly.
am i taking a 1 foot "WIDE" section of this?
what is the 15 ft value? they are taking the 1 foot value PERPENDICULAR to the BEAM and showing a "tributary area" of 1' "high" by 15 foot wide (which corresponds to a tributary area based on the width of the bays i guess?
and they leave out "1 ft" because it is "implied" in the question when they ask for the "load per linear foot"?
can you run this example so it is 1 foot linear width running in the same direction as the beam and it is 1 foot wide over the beam and if not why is this?
lastly, i don't see how the final value isn't 825 lb/ft since it seems like one of the feet would cancel out. or actually, i think this example should be technically 55#/ft^2 x 15 ft x 1 ft (implied width) so the answer would be 825#.
can anyone bail me out on this? i am sure there will be one like this or similar to the roof sample problem and would like to understand it better.
THANKS

thanks a lot theodore.
i think this one is a lot like the roof problem in the handbook.
but i can’t really visualize the “tributary area”. on the roof example this was taken /along/ the ridge beam. in this case since they are using the 15’ seems like the “implied linear foot” is taken perpendicular to the beam?
also, i don’t see how the units work.
it seems to me the units would be #/SF x feet x feet and the units would be pounds. but they just use the 15’ and don’t use the “implied linear foot” of 1’0”. but even in the example they give it seems like feet would cancel out with square feet and give you pounds per foot.
also i am not visualizing what they are asking for very well. i mean  tots load on the beam would be (Ld + Ll) x 15’ (tributary area) x 40’?! but they are asking for “load per linear foot” which is a term i am not remembering very well i guess.
if i am not mistaken the handbook example asks for “load per linear foot” but forsn’t use the term clearly so folks were saying it is “implied”.
wanted to make sure i understand it so i am not just throwing number together...
THANKS 
hi theodore,
maybe i was looking at this one late. does this drawing of the snow load problem look right to you and if so i guess the tributary area on this example would basically be in the same place (which is why they are using the 15’).
also, it looks like the answer should be in pounds per foot and not pounds per foot squared?
does anyone understand why you don’t just use the “implied” 1’0” in the multiplication and end up with a value in pounds? i guess i never understood this. i mean it is a tributary area of 15’ x 1’ isn’t it? 
sorry. here’s the snow load problem. see sean’s comments and my graphic at the end trying to make sure i understand it...https://are5community.ncarb.org/hc/enus/community/posts/115008677508wheretolearntosolvethissnowloadstructurequestioninPDD?mobile_site=true

Jonathan, I read your comment on the snow load problem back when you posted it and it looked like you had a really clear understanding based on your diagram.
I think that the issue you are having with the practice problem here is that you're missing the phrase "per linear foot". This is where it tells you that it's looking for the load on 1' of the beam.
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