Roof corner reinf RC moment frame 2

[phuduhudu]

I have seen this question come around a few times but never seen a convincing answer. How do you reinforce the top corner of an RC moment frame. I think that the outside column bars should go over and lap with the top roof beam bars to take care of the moment. When you see details they tend to be where columns go through and then only the beam bars need to terminate but surely at the top you cannot just terminate the column bars with a hook and the beam bars with a hook.

This does make it a bit akward for the contractor though because he has two legs of horizontal bars sticking out of the top of his column and getting in the way. Any thoughts?

 

[ishvaaag]

You are right, even in the seventies the firm where my brother (a civil engineer) worked, Entrecanales y Távora, S.A., had a standard detail to practice as you say, a minimum of 1 m horizontal length of the rebar from the corner running atop the beam or plate.

 

[TXStructural]

Typical detail would be to have 90 degree hooks on bars at the top of columns. These bars should be bent dowels, allowing the placer to position them precisely prior to placement of column concrete. (Shown in CRSI Reinforcing Bar Detailing, page 18-5)

The column pour will stop at the bottom of the beam, allowing 90 or 180 degree hooked bars in beams to lap the column bars across the corner to the depth of the beam. (CRSI Reinforcing Bar Detailing, page 19-7; CRSI Design Handbook figure 12-1)

Shallow beams might require mechanical splices between column bars and beam bars (one of which must be bent), or longer dowels developed in both the column and beam.

Obviously, the goal is to develop all bars before you get to the point where there is demand.

 

[phuduhudu]

Thanks. Presumably, depending on the size of columns and beams then the inside of the bend bearing stress would need to be checked and larger than standard radius bends might be needed on those bends. If you consider for a moment frame the max beam moment is at the face of the column, you start the development length there, by the time you are at the other side of the column in most cases you will still have quite large forces left in the bar.