Question on Flat Plate Slab System 1

[Lion06]

I am hoping to get some input on what is a probably a pretty fundamental question.
I am dealing with a flate plate building with shearwalls for the lateral system. This is an invesigation, not a new design.
The exterior columns are getting moments cranked into them at the tops from the slabs. Is this effect additive on the columns below or does this only need to be checked locally in each individual column and is assumed to be taken out globally at each level by the diaphragms?
Specifically, if I have a 22 story building and there are moments going into the exterior columns on every floor, is the moment that the column on the 10 story sees the sum of all of the moments from the 12 stories above or is it only from the story it is supporting?
I go back and forth with this in my mind. I can see the diaphragm at the story above and below the column taking this moment out, but I can also see this moment just working its way down the column lumping itself onto the moment from the story below it and the one below that.
I've been unable to find anything about this in my MacGregor text (I'm assuming this is more of an analysis problem than a design problem - hence the lack of reference in a concrete text - and I'm a bit ashamed to admit I'm struggling with this in my own mind). That being said, I'm sure I'll get plenty of good input here.
Thanks in advance.

 

[hokie66]

From bending of the flat plate, the column on each level is in double curvature. You only need to consider the moment per floor. Part of the moment goes into the column above, part into the column below each floor.

A different answer would apply if the columns are part of the lateral load resisting system.

 

[Lion06]

Thanks!!

 

[jike]

I agree with hokie66.

Consider a floor with exterior column to the floor below and floor above with the ends fixed. This should give you a good handle on the column moments. Note that the moments will be taken out by the shears at the floors above and below plus the end moments.

 

[Lion06]

I think where I was getting confused was in thinking about a single story moment frame (I was trying to analogize). If you have a moment connection at the beam/column and at the base of the column with only gravity loads, there will be moment at the base. My thinking was that the unbalanced moment from the slab into the column was being sort of split between the top of the column and the bottom.

 

[csd72]

You need to learn how to draw moment diagrams for these types of things so that you can understand the way it works.

A quick sketched moment diagram would have givene you your answer easily.

 

[jike]

It is split 50-50 if the columns are the same size and same height and the same end conditions.

You are probably too young to rememember moment distribution but this should give you everything that you need and if I remember correctly it is only a one cycle distribution for exterior columns.