When I am Designing this building by interactive design in the result I have found that for a column subjected to load and moment which is lower than the column below more reinforcement is being used for the upper column with lower load and moment.Can anyone please tell me why this is happening?
Staad file: FIRE BDG.std
The lower columns in your model does seem to have higher compression than upper columns but the moments are higher in the upper columns. For example for your load combination 3, if you look at the My and Mz moment values for members 8 and 34, you will see that the values for the later are much higher. As column design depends on interaction of axial+biaxial bending, higher reinforcements may be required at columns with higher moments and lesser axial compression compared to ones with higher axial compression and lesser moments.