Cantilever Fully fixation

[perfectaccess]

HI

I just have simple question, in the market you will see a lot of structural engineers saying to extend the top reinforcement of the slab a distance of 1.5x cantilever length. I think this based on practical issue and the scientific reason is to achieve the development length and the full fixation joint, and that why if the cantilever top steel is running is small columns and there is now way to extend the top reinforcement through slab, the columns steel should be bend in the beam or the beam hook should extend efficient distance inside column to achieve fixity (more than ACI requirement of 12 db),maybe say 25 db I suggest. That lead me to other interpretation for continuous beams, at corner where the column is short as well and no way to extend steel, usually practice hook will be 12db, in this situation fixity is not achieved but I thinks this is not necessary as in cantilever case

Guys would love to hear form you,to say if what I am saying is correct or wrong?

 

[KootK]

I just have simple question, in the market you will see a lot of structural engineers saying to extend the top reinforcement of the slab a distance of 1.5x cantilever length

This is a tough one that I wonder about a lot myself. To be theoretically correct, I believe that the top reinforcement should extend into the slab until there is no longer a hogging moment not satisfied by plain concrete. It can be tough to work that using without FEM, however, and it almost always requires a trickle of reinforcement extend way out into the slab. My gut feel is that 1.5 X cantilever stuff hearkens back to old rules of thumb for cantilevered wood beams etc. Marginally applicable to concrete in my opinion.

the columns steel should be bend in the beam or the beam hook should extend efficient distance inside column to achieve fixity (more than ACI requirement of 12 db),maybe say 25 db I suggest.

Yeah. Beam column joints often go more or less undesigned in my experience. Where there is a column above and below the joint, I think that it's usually not a big deal. You get a great clamping mechanism (top and bottom) going on the beam that is great for transferring moment into the column. At roof level joints where there is only a column on the bottom, I feel that the joint should be truly designed as opposed to simply detailed. Strut and tie is one good tool for that in my opinion.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[perfectaccess]

Lovely,what you said ,just make sense with what I agree.

We are in the same boat,,lol