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Contact pressure under 3D solid

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Message 1 of 3
pmackevicius
501 Views, 2 Replies

Contact pressure under 3D solid

Hi, guys,

 

Is it possible to view a contact stress (pressure) diagram between two layers, when analyzing 3D solids?

 

I mean, when I design round plate on rigid foundation, after linear analysis I can view results of pressure under the panel (pNom).

 

But is there a way to view the same results, when modeling 3D solids? I want to analyze reinforced concrete septic tank on soil foundation (also with modeling soil as 3D solids). And I want to determine nominal pressure under the panel (modeled as 3D solid on top of soil 3D solid).

Which “tick” should I mark in the "results" section to get the results?

 

I hope my question is clear 🙂

 

Thank you in advance.

Regards.

2 REPLIES 2
Message 2 of 3

Well, this is a very complex question.

To model the structure as you described you can use a lot of bars that work as rigid link and assign to them the non linear release that phisically describe your problem, so you can model the contact and the lifting. The depth of the soil model have to be (bussinesq) two times than the maximum dimension of the foundation, the real problem, hardly to be solved, is the mechanical charateristic of the material used for soil...

As you can see geotechnic is not mechanic and the soil parameters are very very empiric. This produce a bad results on a very complex model, I suggest you to use a winkler soil model and semplify everything you can.

However, I'm very curious to see your model, pleese send it when it is finished.

Good luck and greetings

PasProStudio

www.pasquiniprogetti.eu

Structural + Detailing engineers
Message 3 of 3
pmackevicius
in reply to: pmackevicius

Well, I am trying to perform these calculations so I could correctly determine the rigidity (kN/m3) of “Winkler springs”, and then will calculate reinforcement of foundation panel (in different calculation model).

 

The coefficient of rigidity is = contact pressure under the panel divided by displacement of the panel, and comes as a function – coefficient of rigidity varies in direction from center of the panel to the edge of the panel (because the displacement in the center of the panel is bigger than near the edge and etc.).

 

Also – other methods of determination of coefficient of rigidity of soil (Winkler springs) (even the calculation method that is given in RST) do not take into account a deformations of foundation panel (the foundation panel is evaluated as infinitely rigid member, which is incorrect).

 

My friend calculated the same problem with Plaxis3D (deformation in Z dir. Smax=68 mm, I have got Smax=63 mm – pretty close), but I have a problem – I do not know how to view contact stresses (pressure under the panel), so I could finish my calculations and get the rigidity of Winkler springs.

 

The thickness of soil layer under the RC foundation panel is calculated according with design codes (so I could compensate the fact, that I perform linear analysis, and deformation properties of soil are also linear – not according to Mohr – Coulomb law).

 

The properties of soil (E (MPa), Poisson ratio, density) are determined by geotechnicians during the field research.

 

So… Any ideas how to view / find out values of pressure under the RC panel? 🙂 I know that it must be something like 100 to 130 kPa, but I need these numbers from my calculations (and not guesswork)…

 

The model:

 

 https://dl.dropboxusercontent.com/u/9093254/Backa_24.rar

 

Best regards

Paul.

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