Recording stress fro Brick8N

[enginbal]

Hi,

I have a brick element created by using Brick8N and I try to get stress output. OpenSees crates the output file but it is always empty. I created an example below so that you could check it out.

Thanks in advance,

Ihsan...

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model BasicBuilder -ndm 3 -ndf 3

#################### Nodes ###############################
node 1 0 0 0
node 2 0.5 0 0
node 3 0 0 0.5
node 4 0.5 0 0.5
node 5 0 -0.5 0
node 6 0.5 -0.5 0
node 7 0 -0.5 0.5
node 8 0.5 -0.5 0.5

################### Fix supports ###############################
# tag DX DY DZ
fix 1 1 1 1
fix 2 1 1 1
fix 5 1 1 1
fix 6 1 1 1

nDMaterial ElasticCrossAnisotropic 1 3500000 2000000 0.2 0.2 800000

#################### Elements ###################
#element Brick8N $eletag $nd1 $nd2 $nd3 $nd4 $nd5 $nd6 $nd7 $nd8 $matTag $bf1 $bf2 $bf3 $massDens
element Brick8N 1 4 8 7 3 2 6 5 1 1 0 0 0 0

pattern Plain 1 "Linear" {
# Create nodal loads at nodes 3 & 4
# nd FX FY FZ
load 3 -1 0 0
load 7 -1 0 0
}

#################### Recorders ##################
recorder Element -file brick.out -ele 1 -mat 1 stress

#################### Analysis ##################
numberer RCM
system BandGeneral
constraints Transformation
numberer RCM
test NormDispIncr 1.0e-3 30 1
algorithm Newton
integrator LoadControl 0.1
analysis Static

[fmk]

the material as written will not return the stress .. it works with tensors and not vectors (as does all code from B.Jeremic) .. you will need to ask the element for the stresses or ask boris to update his code.

this will output the stresses for the element:
recorder Element -file brick.out -ele 1 stress

[Boris]

Hello Ihsan,

I think that we have that output (and others) working, but since our project with OpenSees expired, we now maintain our own source base, used for other projects we work on...

Depending on what you do want to model, and since we use part of OpenSees framework, maybe we could help you with our models, elements...

Boris

[enginbal]

Hello Boris,

Thanks for asking for help.

I have a very simple portal RC frame filled with masonry infill. All elements are modelled with simple elastic materials, infill material is modelled with elastic anisotropic one. So, everything works elastic. Infills are modelled with Brick8N elements. There are no-tension gap elements between the infill and the RC frame.

Briefly, I need to get stresses (or better strains) of those Brick8N elements. That's all...

I can send my set of input files to your e-mail as well, if needed.

Thanks again.

Ihsan...

[rjaeger]

Hello,

I think that strains could be recorded quite easily by adding the following code to the getresponse function of the brick8N element:

Code: Select all

case 4:
{
    int count = r_integration_order* s_integration_order * t_integration_order;
    int i;
    straintensor sts;
    InfoS(0) = count;
    
    for( short GP_c_r = 1 ; GP_c_r <= r_integration_order ; GP_c_r++ )
    {
        for( short GP_c_s = 1 ; GP_c_s <= s_integration_order ; GP_c_s++ )
        {            
            for( short GP_c_t = 1 ; GP_c_t <= t_integration_order ; GP_c_t++ )
            {    
                i = ((GP_c_r-1)*s_integration_order+GP_c_s-1)*t_integration_order+GP_c_t-1;

                sts = matpoint[i]->getStrainTensor();
                InfoS(i*6+1) = sts.cval(1,1); //epsilon_xx
                InfoS(i*6+2) = sts.cval(2,2); //epsilon_yy
                InfoS(i*6+3) = sts.cval(3,3); //epsilon_zz
                InfoS(i*6+4) = sts.cval(1,2); //epsilon_xy
                InfoS(i*6+5) = sts.cval(1,3); //epsilon_xz
                InfoS(i*6+6) = sts.cval(2,3); //epsilon_yz
            }
        }
    }
}

**This code is modified from the stress recorder

You will also need to change the case number to match a new if statement in the setresponse function. It should be relatively straightforward if you look at the code for this element.

-Robbie Jaeger