Torsion Link Detailing 1

[struggle66]

Hi Good Day everyone,
I have PTB + Hollow Core Slab (HCS). Beam Torsion links and my tendon are clashing each other.

My question are
(1) Is there any other common detailing to avoid the clashing like the blue color closed link as shown. Is it feasible?

(2) HCS specialist told me that their design is continuous because they have the bars coming out from HCS into the PTB (Red Colour Bars As Shown). Can it be?

Thanks

 

[KootK]

(1) Is there any other common detailing to avoid the clashing like the blue color closed link as shown. Is it feasible?

From a torsional capacity perspective, you could probably forgo all of the closed stirrups other than the ones shaded in pink. What you really need those green stirrups for is to serve as primary corbel flexural reinforcement for the bearing "nibs" projecting from the sides of the beam. And, used for that purpose, you would need to stick with the green tie arrangement. The blue tie arrangement would not anchor the flexural nib reinforcing sufficiently.

Your prestressing tendons aren't draped are they? Usually, I see these kinds of beams outfitted with straight prestressing strands that are located fairly low within the beam (best for moment capacity) and out of the way of the lower reinforcing hoop.

(2) HCS specialist told me that their design is continuous because they have the bars coming out from HCS into the PTB (Red Colour Bars As Shown). Can it be?

I suppose that it's possible given properly anchored rebar. I've never seen it done that way though. By "continuous", might the specialist mean that the precast elements are well tied together rather than truly continuous in the flexural sense?

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.

 

[hokie66]

Agree with KootK. The blue tie arrangement is not acceptable, as you can never rely on reinforcement bent around a re-entrant corner like that.

The tendon needs to be moved down. If that presents a cracking or upward deflection problem, you may need a tendon above the corbel as well.

As to flexural continuity of the hollow core slabs, it can be done, but is not normal practice.

 

[struggle66]

Hi KootK, hokie66,

Thanks

1. Actually I've got enough space to provide anchorage for green bars and stop before the tendons. Tendon have drape since it is a continuous beam in a building. If I use soap film approach, I can see the nibs aren't important for torsion. is it? Anyway I definitely need to study more .

2. If there is flexural continuity in hollow slabs, can I consider compatibility torsion for the beam?

I am always asking basic question in this forum and sadly I can't help others. Hope that one day I can be like you.

 

[hokie66]

From your sketch, it certainly doesn't look like you can get anchorage of the green bars between the inside corner and the tendon. What is that distance?

Yes, if the slabs are continuous and reinforced in the top, you could avoid equilibrium torsion problems.

 

[struggle66]

Hi Hokkie,

Sorry for my sketching skill. Actually the beam is 2 m wide with 150 mm bearing length for HCS on each side.

 

[struggle66]

And I forgot to say that this is designed by worldwide well-known structural consultant (American Based) and we are just PT material supplier. On their drawings, the green bars are clearly stated as torsion links.

 

[KootK]

That is a tricky problem struggle66. It's a little odd but the black tie shown below, combined with rebar end anchors, might be one way to solve your problem. The black ties would migrate vertically along with your PT tendons for as long as necessary. I'm a little jealous of your job. I've always wanted to try my hand at working for a PT supplier.

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.

 

[hokie66]

struggle,
I am seldom impressed by knowing something has been designed by a "worldwide well-known structural consultant", mostly because I have worked for same, and know that they don't always get it right.

How does the consultant respond to your RFI's, assuming that you have asked for clarification on the clash of reinforcement?

I am not an authority on inverted T beams, but am surprised that a 2000 wide beam would have all its PT in one tendon.

 

[struggle66]

KootK,

Don't be jealous . I don't have neither mentor nor technical base in my company. I always had to go the hard way. Although I don't mind to do it by myself, I really do not want to compromise the safety of people.

hokkie66,

I met with structural consultants yesterday. They've allowed me to adjust the so-called torsion links to give way to tendons.

You are correct there are 2 X 19 strands inside the beam.

The space between the links will become so big. I will highlight to the contractor to add additional links in between at that location.

Thanks

 

[hokie66]

Good to hear that you are able to converse with the structural engineers. There seems to be a spate of folks on this site who, for one reason or other, are not talking to the responsible designers about issues of this sort.