Lap Length of Reinforcement

[newbuilder]

With reference to BS 8110 cl 3.12.8.13

Should the factors of 1.4 or 2 be applied to wall and column reinforcement?

Is the wall or column surface "the top of section as cast"?

NB

 

[Ginger]

Generally, I would say not.

This condition of increasing the lap of bars in the top of the section as cast is based on the premise that plastic settlement of the concrete occurs around the top horizontal bars in a beam. This leaves water filled lenses below the bar which in turn reduces the bond strength of the concrete to the rebar. Therefore, use longer laps to compensate for this effect.

Obviously, in columns cast in-situ this will not be the case. ther are other factors included in the BS8110 recommendations such as corner distances and relative rebar sizes, but I would not personally worry for the case of columns.