Why do we use circular reinforcement bars in civil construction?/Why reinforcement steel bars are made round in shape?

Let us discuss the 5 reasons for providing a circular shape to the reinforcement bars.

1. Equal load distribution:

In circular bars, the distance from the center point to its periphery is equal in all directions, but the same is not true in all other shapes. So, when stress is applied to the reinforcement bar, the round shape distributes them evenly, all over the section.

As you can observe in the above drawing, the diagonal length of the square section is more than the length & breadth of the section. Therefore, the applied stress won't get uniformly distributed all over the square section. The stresses get accumulated at the diagonal end, which is not preferred in the structural design. 

2. Cost-effective:

The steel bars are manufactured by passing the red-hot materials through a series of rollers. The round shape is much easier to produce as they don't have edges. Square or any other shape needs chamfering work at the edges that add a piece of extra machinery. 

In the case of circular shapes, the manufacturing of different diameter bars is easier & faster. The savings in production time, machinery, & labor make the round shape, a more cost-effective option than any other shape.

3. Easy to bend:

In the construction field, we need to cut & bend the reinforcement bars as per the design requirements. Out of all the shapes, the circular bars are easier to bend & work faster.

The corners of the stirrups made of circular bars produce uniform curvature, without any cracks. The other shapes may get dents or cuts at the corners, which is not advisable. 

4. Orientation & twist:

Note: The size of the bars is magnified for your understanding.

When we erect the bars of columns, the individual bars may twist or orient slightly. In such cases, the round shape does not affect the binding & installation process. The rotation of bars won't disturb the c/c distance & concrete cover.

Other shapes when twisted or rotated, are difficult to work with, due to their corners. The c/c distance & effective cover may change slightly, due to their higher diagonal length.

 5. Center of gravity:

The CG of the circular shape does not shift from its center position when rotated in either a clockwise or anticlockwise direction. 

However, the CG of the square or rectangular shape changes its position when rotated. This affects the load distribution pattern of the structure, as we cannot check each & every bar to be on the perfect axis.

Other advantages:

◆. Concrete flow:

When we pour the concrete, the round shape of the bar does not disturb the flow of concrete. The corners of the square shape may stop the easy movement of coarse aggregates.

 In heavily reinforced structures, the rebars having cornered edges may help in producing honeycombed concrete surfaces.

◆. Threading for coupler:

It is easier to thread round steel bars for joining with couplers. Threading needs extra effort in other shapes & in this process, the size of the bar gets reduced.

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