concrete moment frame - beam/column connection

[Structures33]

Hey all - I am working on a large analysis project. There are about 15 different buildings (already constructed or under construction) and all of them use the same concrete moment frame as the main LFRS. The original drawings do not have a lot of detail so the construction details were in question.
We just recently found out that the column reinforcing does not hook into the continuous beams. It extends up into the beams but does not hook.
It's my understanding that whatever moment is in the beam at the support needs to be transferred into the column by way of the reinforcing -- can the transfer occur if the r/f is not hooked?
Thanks

 

[prsconsultant]

Typically I would so no. If you have a very deep beam and if the column vertical bars extend enough to atleast partially develop, you may expect some moment transfer. If you know of the bar sizes, beam depths, and how far the column bars extend it would help to respond.

 

[Structures33]

Column verticals are #5's, beam depth is 20" everywhere and I have only seen pictures showing how far the verticals extend into the beams - It looks like they extend up to the top r/f of the beam - say 17" of development in the beam. Tension development for #5 would be 35", hook development 14" (but there are no hooks).

 

[JAE]

It depends on how the beams were designed. If the assumption was that they were pinned, then the slip/release in the vertical column bars wouldn't necessarily harm the behavior of the system.

If the beams were designed based upon fixity and moment transfer into the columns, then the bars must be developed. But with As(req'd) / As(provided) applied, the 18 inches might be enough.

 

[Structures33]

I thought a concrete "moment frame" required a fixed beam condition at the supports ??

 

[JAE]

Hey...you are right, Structures33 - I failed to note that in the title and in the post - please neglect my first paragraph above.

 

[csd72]

Check the development length for the moment, you may find that it is sufficient.

Also, if the columns continue to the floor above, then the moment can be transferred via concrete compression struts from the columns above and below.

 

[abusementpark]

Why do concrete moment frames have to fixed at the supports??

 

[JAE]

They are talking about the fixity between beams and columns which are, by definition, what a moment frame is.