can OpenSees solve complete Soil-Structure Interaction (SSI)

[ebe79442114]

According to this book (SOIL-STRUCTURE INTERACTION), page 5, after equation (16.7) :

csiberkeley.com/Tech_Info/16.pdf

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Most structural analysis computer programs automatically apply the seismic loading
to all mass degrees-of-freedom within the computer model and cannot solve the SSI
problem. This lack of capability has motivated the development of the massless
foundation model. This allows the correct seismic forces to be applied to the
structure; however, the inertia forces within the foundation material are neglected.
The results from a massless foundation analysis converge as the size of the
foundation model is increased. However, the converged solutions may have avoidable errors in the mode shapes, frequencies and response of the system.
To activate the soil-structure interaction within a computer program it is only
necessary to identify the foundation mass in order that the loading is not applied to
that part of the structure. The program then has the required information to form
both the total mass and the mass of the added structure. The SAP2000 program has
this option and is capable of solving the SSI problem correctly.

RESPONSE DUE TO MULTI-SUPPORT INPUT MOTIONS
.
.
.
The SAP2000 program has the ability to solve the multi-support, soil-structure interaction problems using this approach. At the same time, selective nonlinear behavior of the structure can be considered.

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In OpenSees days 2008, Mr Pedro Arduino mentions that OpenSees capable to solve the Soil Structure Interaction problems (e.g. response of pile foundation ,bridge bent, or complete structures embedded in soils to earthquake excitations)

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QUESTION:
I want to know can OpenSees solve complete Soil-Structure Interaction (SSI) problems?
Can OpenSees solve the equation of motion for SSI problem while the mass of the foundation does not contain in the right-hand side of the equation and appear in the left-hand side of the equation?

[ebe79442114]

I asked this question because I work on SSI problems .I have experiment results from laboratory test. My model is like below:

freeimagehosting.net/uploads/cdfb754f8d.jpg
freeimagehosting.net/uploads/024f60c0cb.jpg


4 type of structures(5,10,15,20 stories) lie on the two type of soil(Vs= 310,450).

I used pressure Independent Material to model soil. Structures are linear elastic.

My result in free field motion is good, this are some result:

Elcentro 0.05g:

freeimagehosting.net/uploads/d62f536900.jpg

Elcentro 0.2g

freeimagehosting.net/uploads/50cae884db.jpg

Tabas 0.2g

freeimagehosting.net/uploads/ef07878059.jpg

frequency sweeper:

freeimagehosting.net/uploads/36fbaa4555.jpg

My structures, for example 10 story is like below:

freeimagehosting.net/uploads/92ee37ae19.jpg

My problem is when I analyze SSI the result is not good. For surface it is not very bad, but for buried structures it is bad.

Surface structure:

freeimagehosting.net/uploads/daf7e842c9.jpg
freeimagehosting.net/uploads/ada444c5d2.jpg


buried structure:

freeimagehosting.net/uploads/99d6ba15d7.jpg

In prof. boris jeremic lecture notes (sokocalo.engr.ucdavis.edu/~jeremic/CG/LN.pdf), chapter 8 , in page 224 they have been analyzed a 2D model. The model constructed in opensees? Is that a 3D model that they fixed it in out of plan movement? Can you please send me an example of SSI in opensees?

Excuse me, but I really don't know what should I do.

Thanks.

[ebe79442114]

I think I found the problem.

In the analysis I analyze a slice of a soil and base palate(2D analyze), but hole of structure(mass and stiffness). My base plate length in out of plane is 20 m (20 cm in scaled model ). I have been gotten a 1 meter of soil and base plate and hole of structure, while the hole mass and stiffness of structure push the soil in all around the base plate not in 1 meter. Thus I got a slice of soil and base plate with 1 meter length in out of plane and the 1/20 of mass and stiffness of structure. Therefor the result get very beter agreement than past. For assure, I analyzed a structure alone(fixed base) with 1/20 of mass and structure and the result not changed than while I get the hole mass and stiffness of structure.

I think it is like that in the experiment, we distribute the mass and stiffness of the structure in all around the length in out of plane (20 meter), supose strech the structure in out of plane. But the soil and base plate have been strech in out of plane and not needed to strech those.

Is this theory true or false?

please excuse me for my poor english.

[tjcivil]

Hello.ebe79442114.can you give me one example you have done,i am very interested in it.
email:kangshuai2007@126.com

[Unni Kartha G]

hellow ebe79442114,
I am also working on SSI problem, Can you please share one example of SSI? I am having lot of doubts regarding soil modeling in opensees. how did you generate the mesh for your models?
unnikartha@gmail.com

[aneeman]

A common way is to build the mesh in Abaqus, then convert the Abacus output file to opensees bricks. (You have to code the conversion in matlab or C or the language of your choice).

You can get the student Abaqus for like $50, it will do up to 1000 elements.

[quote="Unni Kartha G"]hellow ebe79442114,
I am also working on SSI problem, Can you please share one example of SSI? I am having lot of doubts regarding soil modeling in opensees. how did you generate the mesh for your models?
unnikartha@gmail.com[/quote]