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You may consider defining beams as a bars with a cross section that corresponds to the part of the web under the slab only and increased IY for correct bending moment "transfer". See: http://forums.autodesk.com/t5/robot-structural-analysis/t-slab/m-p/3183798
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Artur Kosakowski
Dear Arutr
Greetings
Thank you for your response.
I am really sorry maybe my inquiry wasn’t clear that is why I modelled the hollow block slab in different way.
Actually , I am wondering to know if this interfere (overlapping) as appear in the capture below causes any increasing (reduplication) in the self-weight or not ?
With regards
Refaat
Yes, they do but I'd say that probably there are a lot of other things that you haven't modelled but they weight (and this is why there is a factor option that you can enter for this type of load in addition to the load combination coefficient) :-).
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Artur Kosakowski
1. “ probably there are a lot of other things that you haven't modelled”
Please, could you explain it?
E.g.the fact that the outer edge of the slab doesn't end at the center of a column or a beam,
weight of foundations, self weight of concrete without reinforcement, weight of welds and additional small steel plates if applicable etc.
2. “ this is why there is a factor option that you can enter for this type of load ”
I have prepared hand calculation for reduction ratio in the attached document. Please could you take a look to it and notify me if you have any comment.
What about dividing bars at the start/end of the overlapped zone and "excluding" the overlapped part of one of the crossing beams from the self weight list?
For the "ribs" - why not model the beams as rectangular ones with the cross section being just the part that is below the slab?
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Artur Kosakowski
Dear Artur
Many thanks for your guidance, I am really grateful.
“ What about dividing bars at the start/end of the overlapped zone and "excluding" the overlapped part of one of the crossing beams from the self-weight list?”
I think, I could do the same approach (dividing) even if I modelled the hollow block slab as panel (orthotropic). Is it correct?
“For the "ribs" - why not model the beams as rectangular ones with the cross section being just the part that is below the slab?”
In fact, to be more precise the ribs modelling as (T - shape) or (rectangular shape) depended on the cross section location along the rib length.
Which means
- The part of the rib length which under tension from top should be modelled as rectangular section (full dimension).
- The part of the rib length which under tension from bottom should be modelled either (T) or (rectangular with increasing the stiffness).
However
Do I understand from you there is a caution if I modelled the ribs as (T-shape) and should be modelled as your approach (rectangular with increasing the stiffness)?
Best Regards
Refaat
“ What about dividing bars at the start/end of the overlapped zone and "excluding" the overlapped part of one of the crossing beams from the self-weight list?”
I think, I could do the same approach (dividing) even if I modelled the hollow block slab as panel (orthotropic). Is it correct?
Correct.
“For the "ribs" - why not model the beams as rectangular ones with the cross section being just the part that is below the slab?”
In fact, to be more precise the ribs modelling as (T - shape) or (rectangular shape) depended on the cross section location along the rib length.
Which means
- The part of the rib length which under tension from top should be modelled as rectangular section (full dimension).
- The part of the rib length which under tension from bottom should be modelled either (T) or (rectangular with increasing the stiffness).
This applies only for meshed slabs. In such situation the slab stands for a flange of a T beam so all you need to 'add" is a (rectangular) web.
However
Do I understand from you there is a caution if I modelled the ribs as (T-shape) and should be modelled as your approach (rectangular with increasing the stiffness)?
I'm not sure if I understand you correctly. My point is that when you define a T shape beam with its center of gravity at the level of the center of the slab the bending moment in this beam will be lower than in reality.
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Artur Kosakowski
Dear Artur
Thanks a lot for your effort to help
“ This applies only for meshed slabs. In such situation the slab stands for a flange of a T beam so all you need to 'add" is a (rectangular) web.”
IMHO when the beams are resisting sagging moments the slab acts as a compression flange then could be designed as (T-L shape beam).
While as when the beams are resisting hogging moments the slab will be in tension and assumed to be cracked therefore the beam should be designed as rectangular section ( full dimension h*bw).
“I'm not sure if I understand you correctly. My point is that when you define a T shape beam with its center of gravity at the level of the center of the slab the bending moment in this beam will be lower than in reality.”
I think you intended that the neutral axis falls within the flange depth (slab thickness). As far as I know in some occasions the neutral axis falls below the flange depth (within the web depth).
Since I don’t know in (RSA) the real location of neutral axis that is why I decided to use (T-shape beam) for hollow block slab in sagging moment zone instead of your approach.
Here, May I ask you this question:
Does RSA take in consideration the neutral axis location (within flange / below flange) when calculate the reinforcement area (required or provided) for (T-shape beam)?
One more question regarding to longitudinal shear at the web-flange interface:
Does RSA do longitudinal shear calculation for (T-shape beam) when calculate (required or provided) reinforcement?
Best Regards
Refaat
Does RSA take in consideration the neutral axis location (within flange / below flange) when calculate the reinforcement area (required or provided) for (T-shape beam)?
Yes, it does.
Does RSA do longitudinal shear calculation for (T-shape beam) when calculate (required or provided) reinforcement?
No, it doesn't.
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.
Artur Kosakowski
Dear Artur
Thank you a lot for all of your explanations
Does RSA take in consideration the neutral axis location (within flange / below flange) when calculate the reinforcement area (required or provided) for (T-shape beam)?
Yes, it does.
It will be very helpful if such calculation appears into the calculation note.
Does RSA do longitudinal shear calculation for (T-shape beam) when calculate (required or provided) reinforcement?
No, it doesn't.
I look forward to give these calculation priority in the wish list due to its importance as one of the design process.
Warm Regards
Refaat
Thank you for posting this suggestion. I have added it to the wish list. Currently (after you determine the required spacing) you may add this reinforcement in the way shown below:
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Artur Kosakowski
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