**Columns with *distributed* axial load applied

[hippo11]

Everyone, if I have a column, say 30' tall, with a DISTRIBUTED axial applied load, i.e. a spiral staircase that's 30' tall and has a triangular axial load diagram in the case when every step is loaded...what do I use for Pu when I'm looking at a bending/axial interaction equation?


If there are say, 60 steps, and if you have 100 lbs per step, the axial load diagram goes from 0 at the top to 6000 lbs at the bottom....Do I take 6000 lbs, then factor, for Pu? This seems overly conservative, as if that would be the same thing as when 6000 lbs are at the very top, producing a constant axial load diagram of 6000 lbs...Or do I take an average, of 3000 lbs? Or just use the Pu corresponding to my maximum moment location (if I do this is my L still the full 30 ft?

Thanks.

 

[dawn836]

well you must consider two cases:-
1- maximum M with corresponding P
2- maximum p with corresponding M