Nice question!

I am assuming your question is to compare both columns under axial and combined loading,

Regarding the pure axial loading, I believe both are similar. However when it comes to eccentricity, the square/ rectangular is stronger.

I think circular shape..

Why Dr. ?

because Ix =Iy z nd have miximum radius of gyration

really good answer from dr. abbas

Dear Dr. Abbas

Are there any experimental tests support your thought ?

Hello Please send your question because the deal have to be able to help my more

But generally circular cross-sections for the central symmetry that are more tolerant times and in all directions and meter problems such as reinforcement of

Dear Mr. Mehdi

I couldn't understand you.

Please try to explain

Thanks 

It depends on your building's plan, it means you need to see in which direction you need more moment resistance.

if Y-axis needs greater moment capacity than X-axis, it is not economical to use circular or square sections.

Good point of view Mr. Mohamad.

Thanks for it.

Circular is the preferred shape because it is the easiest for the contractor to form. Note that it is common practice in some regions to use a helical spiral with the pitch equal to that for a tie.  One has to use the capacity factors for tie instead of spiral, but the reinforcing cage is easier for the contractor to assemble.    

Thank you Mr. Robert Magliola

But the architecturals don't prefer circular columns. Except in the building front, square or rectangular columns is more suitable with walls as they believe. 

My experience in designing of common building shows that, rectangular column needs less reinforcement so rectangular column is more benefit.  I think, its because of shape of plan. Also by using of rectangular column, we can obtain different moment inertia in different direction.     

Thank you Dr. Mehdi Moghaddasi for your thought.

I appreciate it indeed.

Dr Mohannad, it is a design calculations, no need for experimental tests.

Confinement is achieved more if we use circular shape.

I'd like to recommend you to select a circular shape for the column, because it's strong to resist earthquake event.

Yes Mr Jain Hong Wang

Dr.Abbas

Which give more strength, the cylinder or the cube ?

for the same area, standard cylinder give more strength.

Dear colleagues

If you like, see the attached file please

Dear Mohannad ..very interesting question and the group of answers are so much interesting..thanks

Thank you for your opinion Dr. Amjad.

The column choice is, as always, an optimisation process.  It is a combination of structural demands, architectural requirements and construction suitability.  There is no reason to prefer any one shape over another until this optimisation process has been explored.  Even V-columns and y columns have a place.

Agree with Gordon Chirgwin

From structure point and optimum shape for column, the shape is rectangular section. The longer dimension in the direction of moment if all other variable is fixed. 

Thanks Dr. Amjad.

Thank you Mr. Gordon Chirgwin. I appreciate your point of view.

Thank you Dr. Nazar. I appreciate your point of view.

Thank you Dr. Abdulmuttalib Said.

 I appreciate your point of view.

dear Dr. Mohannad,

1. Circular section can use spiral type stirrups which is more effective compared to square shape stirrups. So circular section will have higher column compression capacity compared to square section with the same stirrups ratio. It is also easier to strengthen in the future.

2. Circular section will have same moment capacity in all directions. If the section area is equivalent with square section, the moment capacity will almost be the same.

3. In are where seismic source can be estimated accurately and thus the direction of long distance earthquake can be predicted accurately, the use of rectangular section with longer side parallel to earthquake direction may be more effective to resist large earthquake load. If the source of earthquake is near, the vibration will come from random direction, so the use of circular section will be more effective.

4. For small buildings or houses requires large open space, the use of L shape columns will be better than circular section, because circular section is not very effective for small size column.

Best regards,

Nathan Madutujuh

I agree with Mr Nathan

Dear Dr. Abdulmuttalib Said, you preferred the rectangular section while Mr. Diar Askari said “Circular cross-sections have higher resistance to bending moment and deflection than rectangular cross-sections”. Can you illustrate your opinion mathematically please ?

Dear Mr. Diar Askari, you said “Circular cross-sections have higher resistance to bending moment and deflection than rectangular cross-sections” while Dr. Abdulmuttalib Said preferred the rectangular section. Can you illustrate your opinion mathematically please ?

 Dear Dr. Nathan Madutujuh, I agree with you that circular section has the same moment capacity in all directions, but I think the moment capacity of the square section will depend on the orientation of the neutral axis.

Dear colleagues, although seismic design is very important, but more than half of the word is out of an earthquake zone. Therefore, should the designer take into account earthquake load ?

Theoretically, when a structure is analysed for horizontal loads like wind & seismic, certain factors like frequency and base shear depends on the mass of the structure. So, one needs to calculate the base shear and check frequency also and compare the results for wind & seismic cases. Finally design the structure for the critical loads that is arrived from wind or seismic analysis. Hope this clarifies your last question.

Agree with Mr. Debasish Mondal

Thank you Mr. Debasish Mondal for your clarification.

Thank you Dr. Nazar...

Thanks Debasish for this valuable comments.

star shape

Star is good but you have to also account for costs of forming and the whether there is a principal direction of lateral load.

Nice question!

I am assuming your question is to compare both columns under axial and combined loading,

Regarding the pure axial loading, I believe both are similar. However when it comes to eccentricity, the square/ rectangular is stronger.

Thank you Mr. Gordon for your comment.

Hollow Circular sections also have good strength constraining the cross-section area and the main reinforcement ,without considering practicality and cost.However, If Dr. Muhanned asked to consider cost and practicality  that will be completely different question.

Dear Mr. Ayad Al-Rumaithi

I'm focusing on the strength of the column's cross-section.

Dear Dr. Mohannad,

If you are concerned about strength only(under combined loading with relatively high eccentricity). Two types of columns will be more efficient than square and circular:

1- T-shape, X-shape, star shape (usually non-convex polygons)

2-Hollow sections: including hollow circular, rectangular,..etc

However, if the load is almost axial. all sections have similar strength for short columns. (With rounded shape and convex polygons will have relatively higher strength).Moment of inertia and buckling should be taken into account for long columns.

Most of the above sections are not practical for common cases, so the rectangular and circular sections are mostly used.

Dear Mr. Ayad Al-Rumaithi

Could you explain how  T-shape, X-shape and star shape will be more efficient than square and circular ?

Dear Dr. Mohanned

These sections have higher (Moment of Interia / Area ) ratios than square and circle. However, It should be taken into account main reinforcement distribution, stirrups and code requirement for spacing between bars, thickness....etc.

This is good tool to design columns with irregular and voided shapes:

https://www.dropbox.com/s/36krevvkqvl7zdn/ARCYS.exe?dl=0

Dear Mr. Ayad Al-Rumaithi

Based on your idea "higher (Moment of Interia / Area ) ratios", I think hollow sections are better in strength than T-shape, X-shape and star shape.

Thank you Dr. Mohannad,

Yes,Indeed! For example, in the case radially symmetrical sections :

Hollow Circular and hollow regular polygons > regular star polygons > Circular and regular polygons

However, If the void size is not comparable to the section area it might not be always true.

Actually to combine both ideas: Hollow and non-convexity. Hollow regular star polygons might work well.Even better than "Hollow Circular and hollow regular polygons".

Dear Mr. Ayad Al-Rumaithi

What about shear strength and torsional strength ?

Dear Dr. Mohannad

I think hollow circular sections have highest torsional strength. Because of high polar moment of inertia/area ratio and also shear flow is more homogeneous in sections with high radial symmetry. 

However solid shapes have higher shear strength . I think circular shape has the highest shear strength.

Quite a late response to the question. If the column is not likely to fail by buckling but axial compression then non prismatic columns can be stronger that prismatic columns. We have carried out tests on unreinforced concrete columns of equal height and equal volumes of concrete. Columns which buige at mid height and get narrow towards the top and bottom are generally weaker than circular prismatic columns. Conversely columns that are narrow at mid height can be stronger than equivalent circular prismatic columns. we are currently analysing a range of experimental data that also includes reinforced concrete columns. Of course constructing non-prismatic columns using conventional formwork is very costly. However we use flexible formwork which is easier and cheaper than rigid prismatic formwork

Interesting idea Dr. Remo F Pedreschi!

Very Interesting Discussion

Really loved the question as well as the answers

Interesting question answers

the resistance to bending or deflection of a circular cross section is higher than a rectangular cross section with the same area. in addition, the load required to buckle a column with a circular cross section is the same around its perimeter. but a beam with a rectangular cross section may bend first in either of two axes.

Nice subject to discuss ..... Following

For RC column, the circular section is the best.