how to design floor members with axial forces?

[kgr85]

Hi,

Since we normally assign 'rigid diaphragm' at each floor level of the structural model, we don't get axial forces of floor members. So I wonder how other people design members such as top and bottom chords of trusses (for gravity as well as lateral) that laid in the floor level.
I know there are several ways to do that and people usually do with their preference. but i just want to do a quick survey and discuss pros and cons of each method proposed.

Can anyone contribute?

Thanks a lot!
kgr

 

[Lion06]

I do a couple things. First, after I do all the global analysis that I need to, I'll save the model (and rename it "...... - with disconnected nodes"). Most programs give you the flexibility to disconnect certain nodes from the diaphragm. This will help track axial load into the beam in the plane of the floor. You need to be diligent in determining which nodes to disconnect - if you disconnect the wrong nodes, the load will go right into the diagonal brace and never make it into the horizontal beam.

Another thing I commonly do is take the brace, as-is (without any nodes disconnected), and use the horizontal component of the brace below as the axial load in the horizontal beam.