Underground structures

[XIEWENBO]

hello Who did the underground structure dynamic nonlinear analysis
This is my analysis modeling process,

1.Soil - structure interaction model is established
2.The analysis of elastic and plastic of site soil

3.The gravimetric analysis of underground structure
4.The dynamic analysis of soil-structure

Could you tell me the process correctly or not
XIEWENBO Posts: 6Joined: Thu Dec 10, 2015 4:36 am

[skamalzare]

Hi,

Perhaps, an important point you might want to consider is how the structure is connected to the soil. If you connect them before gravity analyses, there is a great chance you will get negative skin friction. Simply, because soil settles during gravity analysis and relative movement between soil and structure develops negative forces.

To solve this, after building your model, you need to:

- turn off the frictional interfaces
- perform the gravity analysis
- reset the deformations to zero (with initial state analysis wrapper)
- turn on frictional interfaces
- let the structure with its weight (or force) move relative to soil to develop the proper skin resistance

Now you can go for dynamic analyses.

I got a little concerned with your second step of computation and I hope this could help.

Bests,
Soheil

[Alexandert]

So, after all:

1.Soil - structure interaction model is established (develop the proper skin resistance)
2.The analysis of elastic and plastic of site soil
3.The gravimetric analysis of underground structure (gravity analysis)
4.The dynamic analysis of soil-structure
5. frictional interfaces
6. Check reset the deformations to zero (with initial state analysis wrapper)
7. Turn on frictional interfaces

Is this correct?
Thanks.

[skamalzare]

It goes as:

1. Build soil and structure model
2. Perform elastic and plastic gravity while interfacial friction is off
3. Reset the deformations
4. Turn on the interfacial friction
5. Perform a very short gravity step (to make sure your model is in balance)
6. Perform dynamic loading

[XIEWENBO]

skamalzare wrote:
> Hi,
>
> Perhaps, an important point you might want to consider is how the structure
> is connected to the soil. If you connect them before gravity analyses,
> there is a great chance you will get negative skin friction. Simply,
> because soil settles during gravity analysis and relative movement between
> soil and structure develops negative forces.
>
> To solve this, after building your model, you need to:
>
> - turn off the frictional interfaces
> - perform the gravity analysis
> - reset the deformations to zero (with initial state analysis wrapper)
> - turn on frictional interfaces
> - let the structure with its weight (or force) move relative to soil to
> develop the proper skin resistance
>
> Now you can go for dynamic analyses.
>
> I got a little concerned with your second step of computation and I hope
> this could help.
>
> Bests,
> Soheil

[XIEWENBO]

Thank you so much for your reply to my question,,,,
Wishes you to work happily

[XIEWENBO]

I should choose what kind of contact element in a dynamic analysis
thanks

[skamalzare]

Specifically in dynamic analyses, I would use zerolength elements with family of Py-Tz-Qz contacts (e.g. PySimple1, PyLiq1, ...).

Just to inform you, I spent lots of time trying to build connections with contact2D elements. My solver failed in almost all the cases. Therefore, I don't recommend using contact2D elements. Instead, as I said above try using zerolength elements.

[shuaicai]

When using the BeamContact2D element, whether or not the gap between soil and structure is retained, and if zerolength element is used , which material is better?

[shuaicai]

skamalzare wrote:
> Specifically in dynamic analyses, I would use zerolength elements with
> family of Py-Tz-Qz contacts (e.g. PySimple1, PyLiq1, ...).
>
> Just to inform you, I spent lots of time trying to build connections with
> contact2D elements. My solver failed in almost all the cases. Therefore, I
> don't recommend using contact2D elements. Instead, as I said above try
> using zerolength elements.


When using the BeamContact2D element, whether or not the gap between soil and structure is retained, and if zerolength element is used , which material is better?

[skamalzare]

It really depends on your analysis. If you are working on static simulations, both BeamContact2D and ZeroLength elements work just fine. BeamContact2D elements work exclusively with ContactMaterial2D. This doesn't let you capture toe effects. ZeroLength elements work with basically majority of materials (e.g. Py-Tz-Qz materials) and you can conveniently use them without essentially defining gap. Moreover, with Qz materials you can capture effects of toe.

If you are working on dynamic simulations, as you can read in Wiki, BeamContact2D elements have problem with integration methods. These connections can destabilize the solution system and cause lots of problems for you. So, I suggest using ZeroLength connections with Py-Tz-Qz materials.

Bests,
Soheil

[francisconazar]

Dear Soheil,

I'm currently modelling a tunnel subjected to an ovalling deformation and so far the zerolengthContact elements work fine (for now, static analysis), nevertheless, I'm interested in knowing how to extend the use of p-y and t-z springs to this problem, in case I decide to extend the model to dynamic analysis and encounter your problem of convergence. I have 2 questions that maybe you can help me answer:

1. My structure is basically a linear tunnel and not a pile, so I don't know if I can just use them directly since I believe the q-z spring incorporate friction along a diameter of the pile, and in this problem there is no diameter, just a 'wall' (lining).
2. Do you know any references for the curve parameters (pu, ymax) for other soils (e.g., gravelly soils) ? I'm having a hard time searching for the values to use.

Thanks,
Regards.

[shuaicai]

skamalzare wrote:
> It really depends on your analysis. If you are working on static
> simulations, both BeamContact2D and ZeroLength elements work just fine.
> BeamContact2D elements work exclusively with ContactMaterial2D. This
> doesn't let you capture toe effects. ZeroLength elements work with
> basically majority of materials (e.g. Py-Tz-Qz materials) and you can
> conveniently use them without essentially defining gap. Moreover, with Qz
> materials you can capture effects of toe.
>
> If you are working on dynamic simulations, as you can read in Wiki,
> BeamContact2D elements have problem with integration methods. These
> connections can destabilize the solution system and cause lots of problems
> for you. So, I suggest using ZeroLength connections with Py-Tz-Qz
> materials.
>
> Bests,
> Soheil



Dear Soheil: Is the model you build 2D or 3D? and can you send me a successful tcl script about the underground structures you built as a reference ? My email : xueleic@163.com Thank you ! Bests, Chengxuelei

[shuaicai]

skamalzare wrote:
> It really depends on your analysis. If you are working on static
> simulations, both BeamContact2D and ZeroLength elements work just fine.
> BeamContact2D elements work exclusively with ContactMaterial2D. This
> doesn't let you capture toe effects. ZeroLength elements work with
> basically majority of materials (e.g. Py-Tz-Qz materials) and you can
> conveniently use them without essentially defining gap. Moreover, with Qz
> materials you can capture effects of toe.
>
> If you are working on dynamic simulations, as you can read in Wiki,
> BeamContact2D elements have problem with integration methods. These
> connections can destabilize the solution system and cause lots of problems
> for you. So, I suggest using ZeroLength connections with Py-Tz-Qz
> materials.
>
> Bests,
> Soheil


My question:Would the nodes for ZeroLength be built exclusively in coordinates of the same with nodes of soil and underground structures ?, can I use the nodes of soil and underground structures directly?

[skamalzare]

- Yes, they should be at same place. Otherwise, you will receive an error that the length of zerolength element is beyond tolerance.

- ZeroLength elements need nodes with same NUMBER of DOFs at both ends. I guess, as long as both soil and structure nodes have same number of DOFs, you should be able to connect them with zerolength elements.

Bests,
Soheil