Floating column

[virtualvision]

floating columns should be provided or not if grid changes between floors?
what should be the criteria?

 

[GalileoG]

Excuse my ignorance, but what is a floating column?

 

[virtualvision]

that is column is not above column but erected from beam between two columns

 

[msquared48]

I've never heard that term either.

Guessing, are you talking about a column that is transferred out over a transfer beam to two other columns, so that it does not exist below the transfer beam, and is, in a sense "floating"?

Mike McCann
McCann Engineering

 

[virtualvision]

yes it is erected from the beam.

 

[hokie66]

I would not call any column a "floating column". If it is a vertical member in compression, it is just a column. It does not matter whether it is supported on a footing or on a beam. Whether or not you need a column at a particular location depends on how your structure is framed, and there can be no general criteria.

 

[msquared48]

The grid location is your choice and that of the Architect. The vertical forces have to run to the foundation via the column/beam arrangement regardless of the gridlines chosen. The positioning of the columns should come first per the Structural and Architectural requirements, then the gridline assignments. Don't put the cart before the horse here.

Mike McCann
McCann Engineering

 

[virtualvision]

I think earlier it was said that columns should not be eccentric but in this case there is not any column below new column so how one can analyze it?

 

[msquared48]

If you have a transfer beam with columns at each end, where is the eccentricity?

And by eccentricity, I assume you mean either torsion on the transfer beam, or a bending moment to the columns below via a vertical misalignment?

Maybe I do not understand your problem here. Can you post a sketch?

Mike McCann
McCann Engineering

 

[hokie66]

The column is a concentrated load on the beam which supports it. Not sure why you are asking. How much load is on the column, and what is the beam span? Steel structure, concrete structure, or what?

 

[twinnell]

We label these as stub columns.

 

[csd72]

virtualvision,

back to your original question, yes you need to get the architect to specifically state column location on their drawings. If you have problems getting to do this in a timely manner then you need to send them an email stating that this is delaying the design process and copy in the project manager/client.

As far as analysis is concerned, the column is often assumed pinnned at the base and is therefore taken as a point load on the transfer beam. Be aware that if you dont include the beam in the analysis then the sag of the beam will change the actual moments e.t.c. compared to a rigid fixed support, particularly if some of the columns have other columns under them.

So it is better to analyse the whole frame at once if you can.

One thing that has not been asked, is this in a seismic region?