ACI Deep beam + torsion
ACI Deep beam + torsion
(OP)
Does anyone know of a design guide, ACI code reference, or other information regarding concrete deep beams with torsion?
In particular, I am looking for guidance on combining the minimum areas of vertical/horizontal steel from deep beam with the longitudinal/stirrup steel from a torsion analysis. I could combine the steel areas, but the reinforcing gets out of hand pretty quickly. Per commentary, the deep beam vertical/horizontal steel is "intended to control the width and propogation of inclined cracks", not necessarily a direct strength calculation, which might suggest they are not additive?
Thanks in advance
In particular, I am looking for guidance on combining the minimum areas of vertical/horizontal steel from deep beam with the longitudinal/stirrup steel from a torsion analysis. I could combine the steel areas, but the reinforcing gets out of hand pretty quickly. Per commentary, the deep beam vertical/horizontal steel is "intended to control the width and propogation of inclined cracks", not necessarily a direct strength calculation, which might suggest they are not additive?
Thanks in advance






RE: ACI Deep beam + torsion
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.
RE: ACI Deep beam + torsion
I would feel that the torsion reinforcement could pull double duty. It's likely at service level torsion loads there would be capacity left in the bars to provide crack limiting. And at ultimate loading no one gives a crap about serviceability they just want it to stay standing.
RE: ACI Deep beam + torsion
When we employ deep beam theory, we are generally making an intelligent, but not quite correct, assumption about the flow of stresses in the member. One of the primary purposes for the H&V reinforcing is to allow a ductile redistribution of forces to occur when a member transitions from the stress distribution that it "wants" to the stress distribution that we've reinforced for.
All this means that, at the ultimate condition, the supplied H&V reinforcing can be expected to be yielded, and therefore unavailable to resist torsion, at some locations within the member that would be rather difficult to predict.
Some questions for the OP:
1) Are we talking about equilibrium torsion or compatibility torsion?
2) What are the proportions of your member? A 300Wx2000H beam will resist torsion quite differently than, say, a 900Wx1200H beam will.
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.
RE: ACI Deep beam + torsion
1) This would be equilibrium torsion. I have a transfer girder picking up a multi-story column above. For "architectural" reasons, the CL of column above and CL of girder/columns below are offset about 6".
2) The transfer girder is about 2'-0" wide x 4'-6" deep.
I am trying to get rid of the eccentricity/torsion all together. The more I look at the load path, the less I like it! For pricing purposes, I combined the steel areas, and that's probably what I will proceed with unless I can find documentation otherwise. The steel is intense, but constructible. Hopefully the price will help motivate the Architect to line things up though!
RE: ACI Deep beam + torsion
Good news: I think that you can forgo the 3D and, instead, just multiply your vertical load by .75/.5 and ignore explicit torsion considerations. The stirrup spacing should be much more agreeable. Use closed stirrups of course.
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.
RE: ACI Deep beam + torsion
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.
RE: ACI Deep beam + torsion
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.
RE: ACI Deep beam + torsion
It is an interesting one to keep pondering though, especially the 3D strut & tie modelling. When I have some spare time I might look into that. Check back in about 30 years though!
RE: ACI Deep beam + torsion
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.