ETABS Column Unbraced Length Issue

Question

ETABS Column Unbraced Length Issue

PhillipA10 (Structural)

(OP)

2 Feb 21 15:53

Hi,

I am wondering if anyone knows how to brace a column at each floor level in ETABS without breaking the column into multiple columns at each level. For example, lets say you have a column that spans 30 feet between Levels 1 and the Roof that is braced at Level 2, Level 3 and the Roof. Assume the floor heights are all 10 feet. ETABS will design the column using 30ft as the unbraced length and not 10ft. I do not want to manually overwrite the Unbraced Length Ratio's in the Design Overwrites because this could be entered incorrectly and lead to incorrect results. Has anyone experience this same issue and how do you resolve it?

Thanks for your help.

jayrod12 (Structural) · Answer 1 · 2021-02-02 18:22:33

If you put a node in the column at the floor height, won't your diaphragm automatically connect it to the rest of the floor? Why wouldn't you just model it as two separate columns but with full moment continuity across the plane?

PhillipA10 (Structural) · Answer 2 · 2021-02-02 18:51:01

Thanks for your reply. I have beams framing into the columns at each level and a rigid diaphragm is also applied. For some reason ETABS still thinks the column's unbraced length is the full 30ft. I don't want to break the column at each level because when I do so it automatically renames the column unique names to an unwanted value. I need the column unique name to be a specific value and don't want to have to go back and reassign them after I break the columns at each level. I hope this helps clarify why I don't want to split the columns at each level.

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ETABS Column Unbraced Length Issue