Column Height - Beam one side slab other

[sybie99]

This is a simple question but I cant find a clear answer in the codes we use:

If you have a concrete column supporting a slab, but also a downstand beam that ties into one face of the column at the top, can you use the column base to slab- or beam soffit as the column clear height?

In this case there is a 1.2m downstand beam. Can the column clear height for bending in the beam span direction be taken as column base to beam soffit and for bending in transverse direction from column base to slab soffit?

 

[BAretired]

Sounds reasonable to me.

BA

 

[msquared48]

I am confused by the terminology here. Can you post a sketch?

Mike McCann
MMC Engineering

 

[sybie99]

Mike see skecth attached

The BS defines clear height of a column, as used to calculate the effective height, as clear height between points of restraint. In this case I would think that the point where beam soffit ties into column gives restraint to the column in one direction. In the other direction (about the other axis) I would say the clear height is at slab soffit. Would this be an acceptable way to go about it?

 

[hokie66]

I suppose you can do it that way, but why not just use the same height as for your other columns? The columns with the beam will see more bending, but I would just use the worst case. Most of the cost of a column is in the formwork and placement of concrete. The KISS principle applies/

 

[sybie99]

I would normally do it that way, but in this case the column base was cast way too low and column starters and 1st lift is already completed. If I reduce the clear height for design purposes the column has more than enough capacity. If the clear height to slab soffit is used, as I would normally do, the column is nearer to its design limit. So just a comfort thing really.

 

[steellion]

I know you're not in the U.S., but ACI defines unbraced length as "the unsupported length of a compression member, lu, shall be taken as the clear distance between floor slabs, beams, or other members capable of providing lateral support in the direction being considered."

I would consider the unbraced length to be to the bottom of the beam in the beam direction.