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AoA SIr.
sir in etabs we often face a problem that in column steel required in uper stories is more then than in lower stories,
but in common practice the load t=on the column of lower stories is more than the upper stories, so please guide me that why etabs gives us such result
admin
First we need to know about Unbalanced Moment.
Unbalanced Moment: Gravity loads on columns consist of an axial load and moments about both axes where the column design moments are caused by unbalanced loading. Such moments are created when there is an imbalance in the loads on one side of the column versus the loads on the other side. Each beam induces a moment equal to the reaction times the connection eccentricity. The unbalanced moment is the difference in the reactions on opposite sides of the column multiplied by the eccentricity.
If in upper story the unbalanced moment is higher than the lower story then rebar requirement will be higher accordingly.
For example, imagine one case that the unbalanced moment is distributed among three members(2side beams+one bottom column) in top story. In lower stories, four members(2side beams+Upper Column+Lower Column) share the unbalanced moment at the beam-column joint. So in top story required rebar will be more than lower story.
Difference in unbalance moment for different floors can be caused by upper-lower floor framing difference,loading difference etc.
engr khalil dawar
Thank you Sir for your kind responce
admin
You can check the full blog writing- https://decode-bd.com/why-does-required-column-reinforcement-in-the-upper-story-appear-higher-than-the-lower-story-and-what-are-the-solutions/
Luckysingh
i am also facing same problem bro