www.sefindia.org

[sathyace]

Dear friends,

Circular columns are mostly used in bridges and other monumental structures since it has more load carrying capacity than square columns.

Though circular column has more load carrying capacity it is not used in all the structures due to the difficulty in form work.

But if we calculate the moment of inertia for both circular and square section of same area there is no major difference.

For example consider a square section of 1mX1m,

area of this square - 1m^2 and circular section of 1.15m dia,

area of this circle - 1.03m^2

Moment of inertia of square - bd^3/12 = 0.083mm^4

Moment of Inertia of circle - 3.14d^4/64 = 0.085mm^4


Can you please check this and provide your suggestions.

On what basis we can decide whether circular,square,rectangular  column has the more load carrying capacity?

Thanks & Regards,
Sathya.

[rajancivildesign@gmail.co]

The circular column have less buckling than square column because  the centroid is symmetry about all the axis. More over by design itself circular requires minimum 6 bars whereas square column requires minimum 4 bars. Circular column will be provided with helical ties at closer interval than square column hence the ultimate load carrying capacity will be 1.05 times more than a square column.
Circular column is provided normally outside the building for aesthetic view purpose whereas square column can be provide inside building. Where projection is restricted rectangular for more span is provided. Square column is preferable for seismic consideration and rectangular column is preferable for wind load is predominant.
V. M. Rajan.

.

[sathyace]

Thank you Rajan Sir.

How we can differentiate the circular and square column by using moment of inertia?

Which one has the more area moment of inertia?

Sathya.

[es_jayakumar]

Dear Rajan Sir,

It seems circular columns are better performers in seismic consideration too.  Please see the observations of Subramanian sir :
https://sefindia.org/forum/viewtopic.php?t=13043&sid=657006bb9d4605119e5b039b098f32ba

Regards,
E S Jayakumar

[rajancivildesign@gmail.co]

The area of square and circular are almost equal but moment of inertia for square column is 1/12 b^4 where as circular column is  π/64 xb^4. You can compare which section have more moment of inertia.
V. M. Rajan.

[sathyace]

Thank you Rajan Sir.

I have calculated the moment of inertia for both square and circular column and both values are nearly same.

Calculation is given below for your reference.

consider, a square section of 1mX1m,

area of this square - 1m^2 and circular section of 1.15m dia,

area of this circle - 1.03m^2

Moment of inertia of square - bd^3/12 = 0.083mm^4

Moment of Inertia of circle - 3.14d^4/64 = 0.085mm^4


Sathya.

[rajancivildesign@gmail.co]

I herewith attached one excell sheet for circular column for M20 mix and steel grade Fy415  for reference. We can generalised the design sheet for any grade of concrete and any grade of steel by programming. It is to be noted that if we provide helical ties the load carrying capacity will be more by 1.05 times normal circular section of circular ring provided.
V.M.RAJAN

[sathyace]

Thank you Rajan sir.

I have another clarification,

Since square section and circular section are having almost the same moment of inertia
Load carrying capacity of circular column is not depend on the moment of inertia of the section?

Sathya.

[badamsundararao]

Dear friend,

    The effect of Moment of Inertia will be quite predominant in case of Lateral loads calculations. Moreover, if you consider a Rectangular column say 300x600mm and if the dimensions are reversed,You will find abnormal variation in Moment of Inertia and is almost 4 times. Even in comparison of Circular column with Square column, you are comparing 1m Square column with 1.15m dia Circular column, that means you are considering Equal MI and adopting Column size. As per architectural aspects 150mm difference is substantial and the shape is dependent on Architectural needs.

[sathyace]

Thank you badamsundar sir,

If we consider 1m square column and 1m circular column,the moment of inertia for square column is more than the circular column and obviously the load carrying capacity of the square column is more than the circular column with respect to moment of inertia.

In most of bridges and metros we use circular columns(piers),

is it due to the more load carrying capacity of circular column or

the symmetrical axis of circular column?

Kindly guide me.