circular concrete column capacity?How economical? 1

[186]

What is the capacity of a 600 mm dia concrete column.Is this a reasonably economical size for a 4 storey building (5.5m x 8 m typical floor layout). The rebar used are 15 Numbers 25 mm High yield=460N/mm2(15Y25) and the concrete grade is 30N/mm2. Dead load =6 kn/m2 Live load=3Kn/m2.

 

[phuduhudu]

186,

You would have to do the load take down calcs taking into account the roof and floor construction, finishes, live load requirements etc. And then in terms of column sizing the most important thing governing size is usually the applied moments. Vertical loads often help resist moments so you need to look at the axial, moment load interaction. There are published tables or graphs of column axial and moment load interactions. I think BS8110 part 3 has them and once you've worked out your loads you could look at these. Carl Bauer

http://www.bauerconsultbotswana.com

 

[186]

Thanks

Is it true to say the axial load is the overall load on and above the considered floor level and the moment is for that particular floor level only

 

[ishvaaag]

Surely is the 8 m span what is forcing the depth. Were not for this, in non seismic areas we have had conventional RC structures with 30x30 and 35x35 cm with 4 or even 5 floors loading, all standing in perfect state of service, maybe up to about 7 m span (the widest, but commonly more modest in the 5 or 6 m range).

In any case, be confident in results gained from code application, as long in the safety side.

 

[Qshake]

Please note that when sizing columns and footing for vertical loads and applied moments to check load cases for minimum and maximum eccentricity. This should be based on the moment divided by the vertical load for a particular load case. It is entirely possible to have large moment and a low vertical load that may result in a corresponding point outside the interaction diagram.

In other words, for all the beginners out there, don't assume that the maximum of everything controls!

 

[186]

Thank u all. How do we design a circular column as a beam?I have tried so many textbooks but exlplanations are not comprehensive enough? suggestions?

 

[LPPE]

Beam-column design is for when you have combined forces (bending and axial). An example may be a column in a parking garage. You have gravity axial loads, and impact bending loads.

 

[Angus]

Dear 186

Please check out the following website for a free circular column design spreadsheet to BS 8110:

http:\\

http://www.technouk.com

It also has links to other good sites.

Best Regards

Angus

 

[Polecat]

186:

As you might surmise by some of the comments given herein, the design of columns is very sensitive to the type of loading applied.

You should not even attempt to size your columns until all applied loads have been determined, such as contributing floor loads coupled with the bi-axial bending that can occur when the wind is applied at 45 degrees to the structure. Properly installed shear walls can relieve part of this, but you will always have a certain amount of bending applied to the columns.

Then, as Qshake suggested, you must find the applied eccentricity and use those values to size the member. You can find some design aides for this (including software) at the following sites (Prestressed Concrete Institute, Portland Cement Association & American Concrete Institute):

http://www.pci.org/

http://www.portcement.org/soft/soft_col.asp

http://www.aci-int.org/booktemp/main.htm

http://www.spiraleng.com

If you wish to visit my website, we can discuss these or other issues further.