Moment transfer to columns, beam designed as pinned

[sybie99]

If a concrete beam is designed as pinned at the supports where it fixes to the columns, what is the minimum moment that one should allow to be transferred to the column? If it is designed as simply supported, but some nominal reinforcement is fixed to the top corners of the beam and bend down into the corner columns, some moment tranfer will be possible.

Can one merely calculate what is the beam moment capacity for the nominal steel provided and tranfer this moment to the column?

Once this top reinforcment yields, cracks form, can one now assume zero moment is tranferred into the column?

I have a 14m beam spanning onto columns. If designed as fixed the moments kill the columns and they cannot take the moment. Surely the cracking will be minor cracks as the beam only has to rotate ever so slightly for it to act as simply supported.

Some general pointers on how you handle this very common scenario would be apprciated.

Thanks

 

[structSU10]

The amount of moment transfered to the column depends on its relative rigidity with the beam. This is not a straight-forward relationship as column length above and below the beam, beam span, and EI values can make this number vary. I would guess most columns take 10-20% of the moment, but specific geometry is important.

 

[theonlynamenottaken]

I think that unless you specifically detailed the interface between the beams and columns to act as pinned, that it would be considered continuous and capable of transferring moment as you describe. In that case you would need to adhere to sections 8.3 and 8.4 in ACI 318 (in the U.S.). By analyzing the assembly of beams and columns together your columns would act as rotational springs and would not induce full "fixed end" moments in your beams, as structSU10 is describing.