column reinforcement - crank on top or bottom? 1

[BauTomTom]

Hi guys

I would like to ask you if it does make a difference by column reinforcement when you crank the bars on top or on bottom. See the attached sketch, this expalins it better what I mean.

I see in books both cases but what is the better solution?

And which levels whoul you actually give in the bending schedule. Top and bottom floor or rather beam or suffit level?

Tom Tom


Your file's link is:

http://files.engineering.com/getfile.aspx?folder=15b55a31-41fb-443c-9fdb-3022d0d0d78e&file=crank.jpg

 

[BauTomTom]

oh I found now even a reason more for it, This 3D grafik let me realise that you even don't need different stirrups for the cranked bars. You just continue with one size under and over the slab line

hhmmm... nice so why not to use it?

i see it is practical but I have still the one worry which I put in the sketch. Can't it buckel out at the crank? is this not a weak spot?

TomTom

 

[BauTomTom]

here the other sketch

 

[hokie66]

The sketch you found is just that, a sketch. The location of the crank which you suggest is subject to buckling is exactly the location we were discussing earlier, where I said it is simple statics to compute the necessary restraint force. The bar does not buckle at that point, it bends due to the nonlinear forces. Therefore your ties, be it one, two, three, whatever...need to restrain the force to prevent the bar bending further and spalling the concrete cover.

Another reason for using straight bars from below is to produce a more ductile joint. Where seismic detailing is required, the column ties within the floor can be the same size for the full floor beam depth.

 

[BauTomTom]

Dear All

I must thanks you all very very much for all the valuable informations. You helped me a lot. I hope that we can discuss more toppigs like this. It is really great to hear some opinons from sam senior engineers.

Seriously thanks a lot

BauTomTom

I have a new toppinc already online, also with a sketch ;-)