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Results/Reactions/Soil pressure

Creation date: 10/4/2018 1:10 AM    Updated: 10/4/2018 10:42 AM    soil pressure
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Question:

Hello,

our customer used Results/Reactions/Soil pressure and didn't receive right stress map. She used modulus from subgrade reaction under foundation bench and under floor slab.

Is this due to an error in the model? In general, everything looked good now - except contact stress.

I am enclosing the model.

I would be gratefull for Your help.

Best regards,

Answer:

Hello,

additional information from customer: 
she has also changed to fixed support for foundation bench and modulus of subgrade reaction under floor slab. And still the same problem. There are already large differences in soil stiffness so the floor slab should bend and yet there is no change in the stress.

Best regards,



Hello,

Sorry I couldn't get back to you before I left office!
Actually soil pressure is nothing but the (Reaction)/(Subsidary area).  Based on the assigned springs and obtained reactions, there is a concentrated reactions at certain locations.  Concentrated reaction would mean high concentrated pressure.  Such reactions are expected since some nodes have direct support (Dz support) while some have compression only springs.
If the Dz supports are removed, then the soil pressure is as expected.
The modified model is attached for review.  Kindly let us know if further assistance is required.

Regards,
Nandeep
Technical Manager, MIDAS


Hello,

here are to additional questions from customer:
1. "I see that in the model that I got from you concentrated supports have been preserved (unfortunately, this is a necessity because I have several models in one - they are not connected and I use Ritz Vectors). What function for the modulus of subgrade reaction has been applied? I used Convert to but I did not get the right results."
2. "Referring to our earlier conversation about the reinforcement in the slab - I still think that the calculations are not done correctly ( the top slab - roof slab should be about 800 mm2 / mb - which gives 4 rodes dia16 on 1 meter) while in my model dia 25 @ 150 does not go far. I will add that I have already inserted the crossbeam on additional columns - they should not be at all".

Best regards,

Hello,

customer says that she receive different results after modeling a similar plate (thickness 250mm) in the axis: almost 800 mm2 / mb or similar in sofistic-thesis 800 mm2 / m - without additional beams and poles.

Best regards,




Hello,

About pressure, we will check in today's session.
In midas, we have to go for plate 1D design or shell design.  In this case, I believe plate 1D design would serve the purpose.
Now, for plate 1D design, how the domain is selected plays a very crucial role in deciding the force for which the design is to be done.  Personally, I'd recommend to go for small domains and not to select the entire slab as a single domain, because this would lead to incorrect design forces.
Probable domains that could be made are:
Above domains would all be individual domains, since the forces in each of those could be quite different.  The domains shown in the image above are locations above columns.  Similarly, small domains would have to be made for mid slab location and appropriate reinforcement definition would have to be done.
I am sharing a tutorial for AASHTO on how plate design is done in midas Civil.
Kindly let us know if further assistance would be required.

Regards,
Nandeep
Technical Manager, MIDAS
Model 14-modulus of subgrade.mcb
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Box culvert design as per AASHTO LRFD.pdf
DataImage33.png
DataImage81.png
Model 14.zip
Model 14.mcb
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