Design of T beams

[Anonymous]

Hi,

 I’m using robot to analyse and design a RC framed building with in-situ slabs and down-stand beams to ACI 318. I am currently trying out how best to model these beams for the analysis and design modules and have seen a few other posts on this subject that have been very useful. However when it comes to design I am having a few issues.

1. if I model the beam as a t beam section (where I manually define the flange width etc. in the section definition window, and there is no member offset) the analysis is fine and I can also design the beam with no errors, but the for the top reinforcement, robot RC design puts all everything within the beam width rather than distributing it over the flange. I found a check box in the "reinforcement pattern" window and the "Top Reinf." tab (“Bars distributed for T section on the whole flange length”) which I thought would change this but I have checked it and it still tries to put all the top reinforcement into the web width. Interestingly the top reinforcement required is significantly more than if I was to design the beam as a rectangular section (ignoring the flange) for the same loads and span. I’ve attached the robot test file I’ve been using to investigate this however due to the size limit on the upload ive had to delete all results and the rc beam design inputs. However if you open the file, run it and then try designing the beams on gridline 3 I cant seem to get the design module to distribute the top bars through the flange. Can you have a look and see what’s wrong? I expect it’s something very simple that I’m missing but it’s frustrating me at the moment.

2. When I model the T beam as a rectangular section offset from the slab (so that the moment in the beam is largely present as a compression and tension in the slab and beam) again when I come to the design of it I am only designing the rectangular part of the beam. Is there a way to combine both beam and slab so that again the top reinforcement is for this section can be distributed through the slab?

If anyone can help with these two issues it would be appreciated.

Kind Regards

Dmacf

[Artur.Kosakowski]

Please check:

http://forums.autodesk.com/t5/Robot-Structural-Analysis/T-slab/m-p/3185418

http://forums.autodesk.com/t5/Robot-Structural-Analysis/Beam-offsets/m-p/3332921

If you find your post answered press the Accept as Solution button please. This will help other users to find solutions much faster. Thank you.

[Anonymous]

Hi Artur,

Thanks for you reply - I had seen these discussions already and in fact they are the ones i refer to as being useful however they dont deal with my questions which was to do with how to distribute the top reinforcement through the slab when designing a T beam. Can you provide any guidance on this? as i mentioned in my initial post, there is a box that you can select which is called "Bars distributed for T section on the whole flange length" but even if i select this it still only puts the top rebar in the slab

Thanks

Donald

[Artur.Kosakowski · Accepted solution]

For the design the T beam the flange is included in calculations. If you want the top bars to be differently distributed than what the Robot proposed (which is usually in the 'rectangular' part) you can select some top bars and move them into a new locations. You may also create some bars in the flange (e.g. these that you know that are there based on the design of the slab that you already performed) and then run beam verification for frozen reinforcement. This may allow you to e.g. delete some bars from the 'rectangular' part or reduce their diameter.

If you find your post answered press the Accept as Solution button please. This will help other users to find solutions much faster. Thank you.