What is Longitudinal Reinforcement in Column

Offset bent longitudinal reinforcement means the bending of vertical reinforcement bars of a column (bigger column) at a specific storey with the purpose of providing the bars across the limit of a column over (smaller column).

The highest slope of the bent bars should remain 1 in 6. Besides, it is necessary to arrange additional ties for the area adjacent to the bent bars to defend the forces caused by bar bending.

If the face of the column above is offset at 75mm or more from the face of the column underneath, then offset bent is not taken into account but joining of column bars is done with individual dowels.

Necessities of Offset Bent Longitudinal Reinforcement in Columns:

1. The highest slope of the inclined section of an offset bent bar with the axis of column should not go beyond 1 in 6, ACI 318-14.

2. Segments of the bar over and below an offset bent should be parallel to the axis of the column, ACI 318-14.

3. Extra lateral ties, spirals or segment of the floor construction are perfect instances of horizontal support which are arranged close to the point of bend to resist the transverse force caused by the alteration of direction at the bend.

4. Horizontal support already arranged should be designed to withstand 1.5 times the horizontal element of the computed force in the inclined section of the offset bars.

5. When lateral ties or spirals are applied, they should be arranged not in excess of 150 mm ahead of the points of a bend.

Also Read: A good construction document on design of reinforced concrete columns

6. Offset bent bars should be bent prior to place them in the forms.

7. If the offset among the column faces surpasses 75 mm, the vertical bars in the column underneath should be discontinued at the floor slab, and joining of column bars with dowels is required.

8. Dowels can also be applied if the placing of part of the structure is deferred, and also among different units of structures (like footings and columns).

9. Dowels bar size and grade should contain the similar size and grade since the bars are connected, and should contain adequate length to be joined with the main bars.

10. Identical to bent offset, when column bars are joined, there should be additional ties at and near the ends of spliced bars, to arrange confinement to the extremely stressed concrete in the regions of the bar ends.