Recently I have tested some columns of square and rectangular cross sections, made with the same grade of materials keeping the same height to thickness ratio but varying cross sectional dimension. The dimensions of the square column are 150 mm x 150 mm x 1500 mm and those of the rectangular column are 150 mm x 230 mm x 1500 mm. I have found that square columns posses greater strength (P/A) than rectangular ones. I have gone through the literature to understand this effect but I could hardly find any literature that gives a proper explanation. What could be the reason or mechanism behind this effect?
According to the dimensions you provided rectangular columns should give the higher load taking ability. It follows the simple rule P=f * A. P will increase as A will increase.
According to your test result what % of more load is taken by square column, can u shear that with us?
I think there may be other issues involved (like experimental or technical fault) for which this non-realistic result you got.
Yes you are true and I have also got higher value of P for rectangular column. But the strength or stress i.e., P/A of rectangular column is found to be lesser than square column. So whether this finding is correct or otherwise what can be the reasons.
Did you take buckling into account?
When this is the failure mechanism, the rectangular beam will fail at a slightly higher applied load than the rectangular one, but at a much lower stress, because both columns will buckle over the 150 mm axis.
Joi, I am unable to get you well. Actually I have found the load carrying capacity of Rectangular column is higher than square ones (it may be due to higher MI), but it is vice-versa in case of stress or strength i.e., P/A. So whether this finding is correct or otherwise what can be the reasons. The columns are short columns so buckling is unexpected to occur.
Mr. Deb Dulal Tripura can u please tell how many columns u tested? If your column no is more than 5 in each type and all of them them gave the same result as u described then certainly there may be interesting topic to carry on a good research!
Mr. Tripura, I am assuming that you are testing reinforced columns, if it is so, in square columns the core sections are under more uniform confinement as compare to rectangular columns which causes the difference in load carrying capacity.
I think you may have problems in the experimental work as theoritically the cross section area of the rec columns is greater than tne square one so it can resist higher loads
Mr. Ahmed, yes you are true and I have also found that rectangular column can carry more load. But the strength or stress i.e., P/A of rectangular column is found to be lesser than square column. So whether this finding is correct or otherwise what can be the reasons.
I agree with what is written above. If the amount of longitudinal reinforcement, cover, confinement, and concrete strength, result in a similar safety factor for both specimens the only reason could be a defect in the positionning of the axial load, misalignment of the column, or variation of the support conditions. In addition note the obvious, the orientation of the rectangular column will give you different results.
Thanks everyone for your valuable suggestions and comments, which helped me to think in new dimensions.
you might find the comparison results between square columns and rectangular columns in terms of initial stiffness, shear strength, drift capacity... from this paper: http://www.concrete.org/Publications/InternationalConcreteAbstractsPortal.aspx.aspx?m=details&i=51685836
As the area of square column is smaller than the rectangular one u get huge strength when compared with rectangular one. P/A matters
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