Hi:

I am new to ADONIS... and also new to finite element method .

I try to make a very simple model for the analysis of a shallow foundation (strip footing). Everything works correctly when I establish an elastic linear model, but things get twisted when I use an elasto-plastic model (Mohr-Coulomb).

I attach a script to generate the geometry, boundary conditions, load and material definition, solve the model and plot y-displacements. One using linear elastic (shallow_le.ajs), another using mohr-coulomb (shallow_mc.ajs).

Can someone give me a hand? I'm sure I'm doing something wrong.

Thank you.

MC is a nonlinear constitutive model (i.e. elasto-plastic). so if the applied load to the system is greater than the strength of material, model is going to fail (or go plastic) and consequently equilibrium is not going to be reached. it seems like your model has similar situation. if you increase the shear strength you will see that eventually model is going to converge but still in elasto-plastic zone. for example I increased cohesion to 10 kpa and as a result model converged as you can see in attached script file.

I highly recommend you to read famous book titled "Geotechnical Modelling" by "David Muir Wood" to understand the concept behind the constitutive models.

one more thing, since gravity is not activated the amount of "density" has no effect in your model but for the future reference you have to make sure you use kg/m3 as unit of density for "stress-pa" and 10e3 x kg/m3 for "stress-pa". for instant if you have 1900 kg/m3 density for "stress-pa" you should use 1.9 for "stress-kpa". by the way it's "density" not "unit weight" detail system of units are given in the manual.

-Roozbeh

Thank you very much for your reply.

I will continue working with the script you attach and the book you recommend.

A greeting.

Hi Roozbeh congratulations for the amazing programs, a question
which means of window state element with triangle "volume" and + ? have you any teoretical reference for the costitutive model to suggest me (in particulrar for the strain softening as implemented in Adonis?
i've do the script attached [for an shallow foundation you think its correct or not)?
can you suggest how to place the foundation below the upper earth surface?
many tnks.
Danny

Hi villofish,

Unfortunately, I did not understand what you meant with "triangle "volume" and + ?".
ADONIS in theory is very close to commercial program called FLAC. So please take a look at FLAC manual to find more detail about constitutive models. http://docs.itascacg.com/flac3d700/common/docproject/source/manual/program_guide/models/models.html

yes strain softening model is also included in ADONIS, you need to specify the strain dependent shear strength via tables and assign the tables to the model. please look at FLAC manual again for detail. unfortunately I don't have any documentation for this.

 your script looks fine to me. please provide me some sketch to explain what you mean by "placing the foundation below the upper earth surface".

-Roozbeh

your script looks fine to me. please provide me some sketch to explain what you mean by "placing the foundation below the upper earth surface".

hi roozbeh.

i've helped him to create the script so i know what he means when he writes "place the foundation below the upper earth surface".

he just refers to depth of the foundation below the soil surface (case df > 0). i've addressed him to tutorial 6 to read about the simulation of the escavation.

maybe, you could write a new tutorial about shallow foundations.

yes, it's almost the same procedure. you just need to excavate to the foundation depth and make sure the lateral displacement of excavated zone side walls are fixed to prevent failure of vertical wall. fixing is handled similar to the boundary condition.