Strap foundation ( beam plus spread footings)
IMHO for a model you should allow for elastic rotations of supports. Otherwise you can use the indicated option directly in the foundation design module.
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Artur Kosakowski
1. Kindly, could you attach the file of your capture?
Here you are.
2. May I use bar elastic ground instead of dividing the ground beam to small parts?
I used unidirectional supports in nodes defined along bars without dividing them but you may use elastic soil instead.
3. How does (the moment transferred to the ground beam) consider in side RC-beam module when this beam to be designed?
It will be "exported" to the RC design module as calculated for a model.
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Artur Kosakowski
Dear Refaat,
1. I want to transfer e.g (60%) of the support moments to the ground beam. Pls, (take a look to the attached capture).
Could you show me how to apply this percentage to the ground beam and use it inside RC-continuous footing module because I suppose to use elastic bar as in the attach file.
In the model the percentage is not to be "defined" but is calculated based on the properties of elements defined in the model and soil parameters (KZ values). I assume that what you refer to is to model a fixed support under a column (no ground beam) > export reactions to the foundation module > define 60% reduction there.
2. May I know , what is the advantages of using (uplift Uz+) here ? . Where I compared the results (w/wo) (uplift) I didn't noticed any difference in the results (NTM and deformation) or something missing with me?.
When a ground beam is "pressed" against the ground along its entire then none. This matters only when part of it would be "uplifted".
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Artur Kosakowski
Personally I would do this at the RC design stage rather than in the model as I can't think of any easy way of obtaining this effect. I would use the reduction option in the spread footing design module and I would add corresponding bending moment load at the end of the beam for design of the ground beam.
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Artur Kosakowski
1. Why do you expect to have the same results? Mind that for RC beam you would need to apply additional load that corresponds to the stress distribution along the continuous foundation (see the attached picture) to make sure that both RC beam and the continuous footing deform in the same way.
2. To get the results you need to block torsional rotations on the supports
3. As I already explained (see http://forums.autodesk.com/t5/robot-structural-analysis/spread-footing-vs-continuous-footing/m-p/394... post 4) out of the plane bending transfer to soil is currently not supported in the RC Continuous footing module. On the other hand my understanding is that a ground beam is intended to deal with bending in its plane only (otherwise you would probably need it to be of T shape instead) whereas the bending in the perpendicular direction is handled by the isolated foundation itself (plus "another" ground beam defined in this direction).
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Artur Kosakowski
Mind that if you have nonlinear model (uplift) you cannot import simple load cases and them allow the RC Design module to create combinations based on the superposition of results of simple load cases but you need to import combinations instead. Otherwise you may use the linear model instead (no uplift).
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Artur Kosakowski
I'm not sure if I understand you correctly. As I view this situation there are two options:
Option #1:
You don't define the ground beam in a model but you assume that it is going to "take" e.g. 60 % of bending from an isolated foundation. You apply fixed support under the column > calculate model > export reactions to the RC Spread footing module and then you use the ground beam option in its parameters to define this 60 % reduction of moments. In addition you create a ground beam in the stand alone mode and you manually apply loads being this 60% of bending obtained for the foundation.
Option #2:
You include a ground beam in your model > calculate it > export results from the model to both RC Spread footing module and to RC Spread footing module (no need for any additional load as the design is entirely based on the defined model).
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Artur Kosakowski
Dear Rafeet,
1. I am sorry for lack of clarity in my last post. Hope it will be clear here.
I would like you to verify and correct the attached file (Ground beam as continuous footing) whether I added the moments at the ends of the beam in the right acting direction (either clockwise or anticlockwise) or not. Based on the obtained moment directions of supports in the main file (also attached here).
I think they should be entered in the directions of the arrows on the picture below (mind that the signs next to values are from the model and may not be correct for the RC Continuous footing module stand alone).
2. (Option #2) in my point of view even the ground beam is included in the structural model and the design is entirely based on the defined model. We need in some cases such as this case (Strap foundation) to transfer apart of moment from spread foundations to the connected ground beam. This transferred moment will lead to stiff beam and heavily reinforced which of course will reduce the rotations of external foundations and prevent relative settlement.
My understanding of what you wrote is:
1. You define a fixed support under a column and ground beam in a model and calculate the model
2. You export calculated reactions to the RC Spread footing design module
3. You design the isolated foundation with 60 % reduction of bending with the use of the option inside the RC Spread footing module
4. You want to export the ground beam the RC continuous footing design module and you want to have 60% of bending moments from supports at the ends of the beam
if so you may:
1. You define a fixed support under a column and ground beam (as a chain of 3 bars for a span with releases defined for the middle one) in a model and calculate the model
1a. After checking the reactions you create new simple load cases with 60% bending moments at the ends of the middle bar of the ground beam (case #2 in the attached model)
1b. You calculate model again
2. You export calculated reactions to the RC Spread footing design module with original load cases exported (case #1)
3. You design the isolated foundation with 60 % reduction of bending with the use of the option inside the RC Spread footing module
4. You export the ground beam the RC continuous footing design module with all load cases exported (to include loads applied or transferred directly to the middle part of the ground beams).
Please post and vote for your idea at http://forums.autodesk.com/t5/Robot-Structural-Ana
lysis/idb-p/93
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
