There are several reasons behind using ties. The following are the main reasons behind using ties in the column.
1- Longitudinal bars are confined by transverse steel tie bars in order to maintain their positions.
2- At the time of concreting it prevents movement of main reinforcement.
3- In order to prevent buckling of column and bursting of lateral reinforcement into the concrete cover under the vertical forces (compression force) especially in the middle of the column by holding the longitudinal bars in position.
4- It improves the ductility of the column.
5- It also improves dowel action of column reinforcement.
6- The lateral ties also confined the concrete, thereby enhancing its compression load-bearing capacity.
Spacing between the lateral ties as per IS 456
Spacing between two adjacent lateral tie is also called as pitch.
The pitch of transverse reinforcement shall be not more than the least of the
following distances:
1- The least lateral dimension of the compression members;
2- Sixteen times the smallest diameter of the longitudinal reinforcement bar to be
tied and
3- 300 mm.
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