soil-structure interaction continuum model

[STKO Team]

I did not understand your question.
Are you saying that if you use the element's body force it shows pore pressure, whereas if you use equivalent nodal forces (VolumeForce in STKO) it does not?

[yuweihwang]

Hello STKO,

Sorry the problem is not clear. I always use the gravity acceleration component to simulate the gravity loading. When I used the gravity acceleration component ( imposing self-weight instantaneously ), the pore pressure can show correctly. However, it seems that the contact interface only works when we use the VolumeForce. But in this case, it showed no pore pressure within the soil even I only fix the 4dof at the ground surface. Is there any way to simulate the pore pressure when we use body force to simulate the self-weight?

Many thanks for your help!

[STKO Team]

I think I found the reason.
Looking into the source code of the BrickUP element:
It uses the gravity acceleration to compute body forces for both material and fluid.

Code: Select all

resid( jj + p ) -= dvol[i]*rhot*b[p]*Shape[3][j][i];

where:
b is the gravity acceleration vector (bx, by, bz)
rhot is the material mass density

and then it also does:

Code: Select all

resid( jj + 3 ) += dvol[i]*rho*(
                        perm[0]*b[0]*Shape[0][j][i] +
                        perm[1]*b[1]*Shape[1][j][i] +
			perm[2]*b[2]*Shape[2][j][i]
			);

rhois the fluid mass density.

So basically, when you set b = 0 in the element property, using instead the VolumeForce, you only compute the force vector for the translational dofs, neglecting the effect of water density.


So what you can do is:

• set b to (0, 0, -9.81) in the element property.
• set the material density (rhot) = 0, in this way the body forces for translational DOFs will be zero (inside the element)
• but at the same time the element is able to compute the second equation, that is, the body force for pressure DOFs
• use the volume force to include body forces for translational DOFs incrementally

Now the only difference is that the body forces for translational DOFs will be applied incrementally, while the body force for pressure DOF will be applied instantaneously, but I think it should work

[yuweihwang]

Hello STKO,

Many thanks for your help.
I will try to use this method to do the analysis.

[BuuNguyen]

Hello STKO,

Many thanks for your help.
I will try to use this method to do the analysis.

Hi Yuweihwang

Did you try the suggestion of STKO? do it work well?
All examples I found in Opensees Wiki usually used self-weight inside the UP element, then applied by 2 elastic and elasto-plastic analysis.
Is there equivalent between them?

I am stuck in using contact element (ASDEmbedded) with UP element during excavation.
Thank you and look forward to your reply.
Buu