Concrete column effective length 1

[Gile_]

I am checking the buckling capacity of some 200mm or 250mm wide concrete columns for a typical apartment and wondering if you would consider it is rotational restrained in this weak axis so k factor can reduced to 0.7?

 

[MotorCity]

You need to define the end conditions of the column and determine the degree of restraint. Is the joint free to translate? Is the joint free to rotate? Is the joint free to rotate and translate? This determination is not an exact science and requires some engineering judgement. The restraint depends on the details of the connection.

 

[Gile_]

The columns are connected to slabs from 250mm thick to 500mm thick using starter bars.

 

[MotorCity]

Can you post a sketch? We cannot see what you are seeing.

 

[Gile_]

Like this. N20 bars vertical bars with 800 lap to starter bars (not shown on the pic)
I think I can treat the bottom one as rotational restrained but not sure about the top one especially when the column width is 200 only

 

[MIStructE_IRE]

If these are braced columns (ie, assuming they’re not part of a sway frame) then personally I’d be taking an effective length of 0.85L. I think you could justify taking 0.75L though based on the below.

 

[Gile_]

Thank you.
Looking at the picture you provided. I am quite surprised that it mentions the depth of the beam/slab only without stating how starter bars should be arranged etc. For example. If the beam/slab depth is greater than the column but the column is precast with single layer of dowel bars to the beam/slab. I doubt that condition 1 applies?

 

[Ingenuity]

If the beam/slab depth is greater than the column but the column is precast with single layer of dowel bars to the beam/slab. I doubt that condition 1 applies?

With a precast column then it is NOT monolithic, so Condition 1 would NOT apply.

Also, who does 200mm (8") wide columns? That is nuts!

 

[MIStructE_IRE]

Sorry, I didnt know it was precast. In that case I can’t say I’d be taking account of fixity. Does 200mm even cover your fire requirements? Its quite a small column.

 

[Gile_]

It is not precast. I was just looking at the picture you provide and think out loud.

 

[MotorCity]

If the slabs are cast separate from the columns, I would use K = 1.0. If the slabs and columns were cast monolithically, I would consider using K < 1.