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Development length

Development length

Development length

Hi all
I am designing concrete beam and column connection
I assumed connection to be fixed but I can not extend negative reinforcement at end column, can I develop bars so that its development length is U shape (i.e. top Rft. will reach end of column then bent down the depth of beam and then bent again and stop with beam Bottom reinforcement

RE: Development length

Your hook development length is only the distance from the column face to the point where the bar hooks (assuming there is a standard hook at the end of the bar).  Bending a bar and running it down to the bottom steel in the beam does nothing to increase development length.


RE: Development length

so if i need fixed beam column connection should i extend my bar inside column? no other way?

RE: Development length

According to ACI 318-02, if you want to develop your bar in a standard hook, you need to meet Article 12.5.  This hook development length is shorter than the straight development length of Article 12.2.  While Article 12.5 includes L and U shaped hooks, no provision is given for hooking the bar twice and running it back along the bottom of the beam.

Note that the advantage gained by hooking a rebar seems to be in conflict with the theory behind Appendix "D", which has downgraded the effect of hooking anchor bolts.

RE: Development length

why not design it as pin connection?  You just need vertical rebars from column to prevent beam from sliding.  Are my thoughts ok?

RE: Development length

i do not care for having standard hook, is it a must to have it?
it is ok for me to develop bar by 55 X Dia. but this will not be achived except if i bent the bar ib U shape

it is difficult for me to consider it simple beam due to large deflection that will result from this

RE: Development length

Extend outside face column bars up, bend and lap with top beam reinforcement as required. Inside face column bars extend up straight and terminate at top of beam. For integrity, extend beam bottom bars and terminate in a standard 180 degree hook over top of column.

Make sure that your column and beam are designed to carry bending moment around the corner.

RE: Development length

I agree with jike, IF there is sufficient hook development length vertically (within the beam depth) and horizontally (within the column dimension parallel to the beam).


RE: Development length

When you say "assumed connection to be fixed" I trust that you mean the connection is rigid, not fixed in an absolute sense. (Apologies if the terms have the same meaning where you are.)

RE: Development length

You might have to use smaller bars, more of them and/or adjust the column and beam dimensions to make all your numbers work.

Good Luck!

RE: Development length

Sorry I meant rigid connection not fixed
the beam is in first floor and the building is two story height so I detailed column bars as extending up the end up of beam by 50 times bar diameter and then will be spliced with bars of column for second floor and top beam Rft. will go till outer face of column then bent down till bottom of beam and then back inside beam at its bottom face
Will it work like this?

RE: Development length

You don't need to bend the beam top bars a second time and extend them back to the inside face of the column.  You do need to check the distance from the inside face of the column to the point where the beam top bars bend down.  This distance must be greater than the beam top bars hook development length, as required by Code.

You should splice the column bars with a Class B lap splice.  50 bar diameters may not be enough lap.


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