HELP. NEWBIE IN ETABS

[winnieval]

I have modeled a two storey building. x=8m, y=6m. 2nd Floor is 3m and bottom is 3.2m. Column is 0.30x0.30m, Beam is 0.20x0.40m, f'c=20.7Mpa, Fy=230Mpa, Con=25KN/m3. Slab=0.125m as shell.
I put slab both in second and top floor. Mesh it with auto mesh. Click the 1,2,3,4 checkbox. Then run the analysis. I noticed that the column at the second floor requires 2702mm2 and at the bottom is only 900mm2. Which is I think is wrong. The bottom storey should require more reinforcing bar. And what is the "O/S" means that shows on beams and columns? And the required steel in beams, I noticed that it is small. Those who have experience in etabs pls help me on how to make my analysis correctly.

 

[Hich]

O/S Means over stress. for columns it is not correct that bottom stories need more reinforcement. because it depends on the interaction between axial force and flexural moment. in ACI code anod most other codes there is a load combination like 0.9D+E in which the live load is neglected. majority of upper stories' columns
are designed due to this load combination. Note that when on the interaction diagram the actions lie in the flexural control zone while axial pressure decreases you need more reinforcement.
Hope it is helpful

 

[winnieval]

Upper column requires 3000mm2, lower only 900mm2. can you send me your sample work on etabs so that i can have a clear view of detailing and anlysis of structure.

 

[winnieval]

I just use the load combination of 1.4DL and 1.7LL. then again the resulting required area of bar at upper column is 5000mm2, the lower part is 900mm2 only. help me with this problem pls
.