Anisotropic nonlin material for infill masonry

[enginbal]

Ciao tutti,

I am trying to model a portal frame including the masonry infill walls by using OpenSees. I plan to model the infill material by 2D 4-node elements (I have not decided yet which one it will be). However, as material, I need an orthotropic material. As far as I see, I have to create this orthotropic material by employing the Template Elasto-Plastic command.

Generally we use von Mises yield criterion with a tension cut-off in order to represent the non-tensional behaviour of the infill walls.

I was wondering if you please give me a guidance on how to create a tension-cut off to represent the non-tensional behaviour of the infill masonry material (even for concrete, we need it).

I am quite beginner ans stuck a little bit. Sorry for my ignorance.

Thanks for your attention,



Kind regards …

[silvia]

you might want to get in touch with Boris Jeremic, at UC Davis.
I believe he developed this material for soils modelling.

[enginbal]

Infact I have already sent an e-mail to him but I thik he is quite bussy nowadays ...

Thanks for help.

[Boris]

I did resond to you (see attached email). In short, Template 3D ep is a set of elastic plastic classes, can be used for any elastic-plastic material (there is a number of models that can be used for soils, rock, concrete, metals...).

Boris

Date: Tue, 19 Sep 2006 12:41:37 -0700
From: Boris Jeremic <jeremic@ucdavis.edu>
To: Ihsan Engin Bal <ibal@roseschool.it>
CC: Boris Jeremic <jeremic@ucdavis.edu>
Subject: Re: A question for the template-elastoplastic
References: <200609191004.k8JA3vUs018770@mx6.ucdavis.edu>

HEllo Ihsan,

There is a way to do it but it would take some programming to get the cutoff
into von Mises.

However! I can recommend using maybe Drucker Prager or even better yet the Leon
model for concrete (that we already have in OpenSees). With Drucker Prager you
will get similar shape as with von Mises but it will be smooth function, while
with Leon model it will be even smoother. That Leon model for concrete follows
work by Willam and Menetrey:



@article
{Menetrey95,
author = { Ph. Menetrey and K. J. Willam },
title = { Triaxial Failure Criterion for Concrete
and its Generalization },
journal = { {ACI} Structural Journal },
year = { 1995 },
volume = { 92 },
number = { 3 },
pages = { 311-318 },
month = { May--June },
note = { },
napomena = { local CM470 ; 04mar97 },
}


Since you use masonry wall, which is pressure sensitive material I would not
recommend using von Mises (even with tension cutoff) but rather one of the
models I mentioned that take into account change of strength with change in mean
stress.

We do not have implementation for 2D plane stress but that is not a problem as
we regularly use solid brick elements (3D) and just make boundary conditions
appropriate for 2D (master slave all in-plane motions). The extra computational
burden for integrating constitutive equations in 3D is negligible...

Best regards, Boris

[enginbal]

Hello Boris;

Really thanks for the answer, it is quite useful.

Sorry for the inconvinience which was most probably caused by my over-filtering mail server.

Really thanks again.