simulation of footing foundation 2

[sendy]

I'm interested in simulation of footing foundation resting on c-phi material (with small cohesion). I am using Mohr Coulomb yield criteria for the soil and prescribing a vertical displacement at some constraint nodes instead of vertical loading pressure.
I observed that tensile stress always occurs at the edge element of footing and it produces unconvergence solution. I think this tensile stress is related with the value of cohesion. I tried to use very small linear-element (under the footing) and it didn't help. Can you give me a hinge to solve this tensile stresses?

 

[fndn]

Are you modeling your footing as flexible? If so, then our footing deforms concave down, thus giving us higher stresses on the edges. Try a rigid footing, and if that doesn't work, change the geometry of the footing, by having a trapezoidal footing(that is a sloping footing base).

As for literature, Duncan, J.M. has done many papers of FEA in Geotechnics. Below is a link for further references.

http://www.usace.army.mil/inet/usace-docs/eng-tech-ltrs/etl1110-2-544/chap-5.pdf

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[sendy]

I modeled the footing as nodes that are tied together (so they will have same vertical displacement) and prescribed a vertical displacement. Thereby, it is a rigid footing.

Thank you for the references.

 

[fndn]

I was thinking something similar to the following image link:

http://www.cee.cornell.edu/research/case_study/cn/img/2_32.jpg

It is for the CN Tower foundation in Toronto. Keep us posted on what solution you arrive at.

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[sendy]

Thank you for the image link.
In the last two days, I have got a plastic-stress contour similar to Prandtl solution by introducing very small elements (0.005x0.005) and very small time increments (0.0005xprescribed displacement). I think the time increment is more sensitive compared to element size. However, it is very time consuming.
Can you give any references to do remeshing method since I heard that it might give better solution and less time consuming ?

 

[fndn]

Here are some links of pdf files and available software:

http://www.iesweb.com/aggradebeam.htm

http://www.uni-stuttgart.de/igs/content/publications/79.pdf

However, describe the footing geometry, loadings if they are concentrated loads, any momements at the ends, soil properties and what deflection and/or bearing stresses you want to stay under, and maybe we can try the long hand solution as a check. Bowles' 88 foundation book has some guidance in chapter 8, but I think his '96 text may have the computer software.

Just a thought, that if the mechanical simulation is comlex, we can try to use electrical circuit analogy, where the displacement would be the electric charge, the moments would be voltage and so on. So books on mechanical vibrations and beam on elastic foundation would come in handy.

By the way, why not input the loadings, and see the displacement output? Very interesting problem-again describe the problem and your requirements.

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