Modifying the Template material

[enginbal]

Dear Prof. Jeremic,

I am an OpenSees user who tries to model the masonry infil material in RC frames. I am modelling the masonry infills with the Leon type failure model associated to Template material, implemented in OpenSees, however, I have a small problem with the angle of the bed joints which is so characteristic for masonry material.

The plain failue criterion of masonry has been defined by two principal stresses as well as the angle of these to the bed joints. This is because of the distinct anisotropic behaviour of masonry caused by bricks and the mortar joints. In fact, having isotropic failure criterion, concrete type Leon criterion matches with the case of 45-degree angle (i.e. a wall having the same height and length) However, I do not know how I can manage to define the asymetric criterion for angles different than 45-degree. How can I shift one side of the criterion towards right-left or up-down (i.e. stretching the criterion towards one of the principal stresses)? I was thinking to impose some initial stresses in related direction to create a kind of translational asymetry but I am not sure if it is correct or not. Is there a more proper way to do that? How can I define the anisotropy (or orthotropy) for that material template? What is the way to define the orthotropy in terms of elastic modulus and failure criterion?


Thanks for your help,

Kind regards.

Ihsan…

P.S. : We had a smilar discussion a couple of months ago, see the message board : http://opensees.berkeley.edu/community/ ... php?t=1641 . Thanks for your previous response. I try to implement what you suggested but the anisotrophy is still the biggest problem.

[Boris]

You can do this in a number of ways.
1. Simplest way to do it is to assign anisotropic elasticity, which would them make the elastic-plastic model anisotropicas well (it will "shift" or deform the yield surface in stress space). This is a good solution if you indeed have elastic anisotropy...

2. if your anisotropy is purely after yielding happens, you can use rotational kinematic hardening with Drucker-Prager material model and start with an initial alfa_ij (whih shows how much is your yield surface shifted at the begining)...


Iam updating lecture notes for next few days, so please check them back by mid next week, you'll see the theory and example at:
http://geomechanics.ucdavis.edu

Boris Jeremic

[enginbal]

Thanks for your answer on that. It is just perfect.

The first way is just for my case. In fact, I have already introduced anisotropic elasticity (ElasticCrossAnisotropic element) but I was not sure if it would also affect the failure criteria.

Thanks again,

Ihsan ...