All the steel reinforcing bars using in construction are of circular section, why there is not bars of square sections?
To answer this question, let's divide the parameters influencing to the subject in different cases:
Tensile or compression stresses and bond stress and the situation of casting and hardening the concrete and also buckling of the reinforcement under compression.
The compression or tension stresses in reinforcement are related to the are of the steel bar and bond stress is related to the circumference of the steel bar, and the ratio of circumference to the cross-section area of the reinforcement is an important factor to check the bond stress and adherence between steel bar and the surrounded concrete.
- For the case of circular section steel bars:
Area A = pi*D2/4 and Circumference p = pi*D therefore: p/A = D/4
_ for the case of square section steel bars:
Area A = D2/4 and Circumference p = 4 D therefore: p/A = D/4
Therefore from this ratio point of view, both of the sections have the same value, i.e.: for tension most probably they may act similar for the bond and adherence, but for the compression steel bars especially in columns, they are subjected to buckling when the concrete cover is lost, in this case the circular bars act better than the square compression bars because they have the same property axis for any directional axis on the section while the square sections have at least two weak axes in two main direction on the section. Exactly like the square columns that are better against buckling compared to the square section columns.
The other local effects at the corners of the square sections fro casting and hardening of concrete and stress distribution at corners are the other factors that locally as well the circular section act better compared to the square section steel bars because of multi symmetry axes is preferred due to the concentration of stresses at the corners, because they do not have any corner while the square sections have.
I hope it is useful for you.
Best of luck.
Thank you very much Dr Kabir Sadeghi for your amazing and wonderful scientific discussion. As you said, I think that the most influencing aspect is that corners of square section may cause premature failure due to cracks initiated at corners because of concentration of stresses.
Best regards
You are most welcome. I am glad that you agree and you are happy of my answer. Yes the local effects at corners make problem and also bucking for the case of the compression steel bars between the stirrups, especially in columns.
All the best.
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