curved slab - U bars - how to place ?

[BauTomTom]

Hi

it is difficult to explain you must see the attached sketch. By a curved slab how would you place the Ubars to close up the reinforcement of the cantilever slab?

90 degrees to the curved edge or would you stick to the parallel bars according to all the rest?

BauTomTom

 

[BAretired]

Where is the cantilever? You should show supports for the slab. If the 'U' bars are containment steel, shouldn't the be outside the main bars?

BA

 

[csd72]

As BA has inferred, it depends on the reasons for the U bars. This is the type of detail that tends to be more common in the UK than anywhere else.

If they are for development of the main bars then they need to lap with the main bars.

If they are for serviceability then you need to thank of where the cracks are likely to be.

As an aside, I would suggest a diagonal trimmer top and bottom along the face of the curve to help prevent cracking.

 

[Teguci]

Save yourself the headache and keep them orthogonal with the main reinforcement. Add more as calcs call for.

Not sure what a diagonal trimmer is (UK term?) but it sounds like a good idea if it means a short developed bars along the curve.

 

[hokie66]

Parallel and tied to main bars. Too many layers of reinforcement if done the other way.

 

[msquared48]

I agree with Hokie, but I would add one or two curved trimmer bars inside the "U" to tie everything together better. Just watch for the bar spacing with respect to the aqggregate size to prevent rock pockets.

Mike McCann
MMC Engineering

 

[RCDetailer]

If I could see the sketch I may be able to help

 

[hokie66]

It's just a JPEG Image.

 

[JAE]

What are these bars purpose? Not sure they actually do anything.

 

[BAretired]

How is the slab supported? What are the boundary conditions? I tend to agree with JAE that the U bars do not do anything.

BA

 

[msquared48]

It could be that if there are top and bottom bars in vertical alignment, that the presence of the "U" bars would serve to develop the ends of the those bars if the lap was sufficient to do so.

As to why, well that's another question.

BauTT: It would be well to get some of your input here.

Mike McCann
MMC Engineering

 

[BauTomTom]

- - to BAretire - -
You are right in best case the U bars should be outside but the problem is that if they go really 90 degrees to the curved wall then they will get into a other layer again.
The cantilever is very short. Around 0.5m so there we don’t need to worry

- - to CSD - -
Diagonal trim along the face? Sorry somehow don’t know how you mean it

- - to Teguci - -
So you would do orthogonal to the rest reinforcement. But why headache? There shouldn’t be anything complicated and for the free curved edge a orthogonal reinforcement would be the best


- - to msquared48 - -
Add one or two curved bars between the U bars? The slab is only 250mm high and still four bars distributed on this hight?

- - to RC Detailer - -
You can see the sketch right in the first meail from me there is a link for it

- - to JAE - -
Our code says, that a free edge of concrete should have such U bars in the edge line. Static wise they don’t have a major reason I think it is just to prevent cracks

- - to msquared48 - -
Let me attached some scans out of my detailing book. This is what I mean

BauTomTom

 

[msquared48]

Bay:

The detail you posted does show two trim bars at the end. It could be one if depth is a problem. The "U" still has to be bent and it has a radius. That's where the trim bar(s) go. No problem.

Mike McCann
MMC Engineering

 

[BAretired]

With a 250mm deep slab and a cantilever of only 500mm, I would put the 'U' bars on the outer layer so that they are confining the main steel. The main steel can easily be bent to accommodate the 'U' bars. A couple of bars conforming to the exterior curve should be included within the 'U' bars and the 'U' bars should be placed normal to the curve.

BA