column unbraced height

[NewbieStruct]

I have a project where a column pokes through a concrete floor(concrete over steel deck - 5.5 total thickness). It will have the concrete floor all around it. Does this qualify as a brace point ? The floor to floor height is 15' and the total height of column is 29'. Is the unbraced length 15' or 29'?

 

[BAretired]

Depends on whether or not the floor at Elevation 15' is adequately braced by shear walls, frames or other elements so that it constitutes a lateral brace as defined in the relevant code. Generally, this involves a strength requirement and a deformation requirement.

BA

 

[Lion06]

I would also want to see a positive connection between the diaphragm and the column. You can justify letting the column bear against the diaphragm for bracing, but I would a positive connection.

 

[NewbieStruct]

Thank you for your response. Sorry I could not reply back, had a family emergency to deal with.

We had the columns moved so that they do not poke through the floor.

In an extension to my question,for an exterior column, that has beams coming on both sides reducing the effective length in x-x direction, will concrete over steel deck brace it in the y-y direction. Is it better to have a joist framing into the column instead?

I had designed the columns to go full height in the y-y direction and my coworker is telling me it is overdesigned. He has always designed columns by assuming them braced by the concrete deck.

 

[TDIengineer]

Refer to Appendix 6 in AISC. The deck could be considered as a nodal brace. Refer to the equations within the appendix for the required brace strength.

I would not rely on concrete bearing along for the nodal brace.