hysteretic material

[Olympia]

Dear all,

I used hysteretic material in a zero length element in order to simulate a bearing. Time history analysis was performed. The analysis results indicate that the bearing displacement is larger than 0.198m (which is value e3p). I'm a little confused and I'm wondering if it is possible since according to the constitutive law, the max displacement is 0.198m?

# build bearing material
set s1p 485.88;
set e1p 0.0594;
set s2p 485.885;
set e2p 0.1975;
set s3p 485.89;
set e3p 0.198;
set e1n -0.0594;
set s1n -485.88;
set e2n -0.1975;
set s2n -485.885;
set e3n -0.198;
set s3n -485.89;
set pinchX 1;
set pinchY 1;
set damage1 0;
set damage2 0;
set beta 0;
set IDhys 10;
uniaxialMaterial Hysteretic $IDhys $s1p $e1p $s2p $e2p $s3p $e3p $s1n $e1n $s2n $e2n $s3n $e3n $pinchX $pinchY $damage1 $damage2 $beta;

uniaxialMaterial Elastic 16 6500000; # vertical stiff
uniaxialMaterial Elastic 11 328000; # torsional stiff
uniaxialMaterial Elastic 17 32800; # rotational stiff

# bearings at the piers
element zeroLength 150 57 157 -mat $IDhys 16 $IDhys 11 17 11 -dir 1 2 3 4 5 6;
element zeroLength 151 59 159 -mat $IDhys 16 $IDhys 11 17 11 -dir 1 2 3 4 5 6;
element zeroLength 152 61 161 -mat $IDhys 16 $IDhys 11 17 11 -dir 1 2 3 4 5 6;



Thanks,
Olympia

[vesna]

e3p is not the maximum strain or deformation. It is just the 3rd point on the envelope curve. The 3rd pint on the envelope curve is used to define the slope of the envelope after the 2nd point on.

[Olympia]

First of all, thanks a lot for your reply.
If I want to define the maximum strain or deformation of the bearing for example the max displacement to be 0.198, how can I do it?
Do I have to use another material?

Thanks again,
Olympia

[Strep]

Dear Olympia,

You can use the MinMax Material

[Olympia]

Thank you very much for your reply!!
My problem is that I want to use a material such as hardening or hysteretic material but I want to define the "length" of all the branches of the constitutive law. For example, the "length" of the elastic branch is defined by the tangent stiff and the yield stress or force for the hardening material, but what about the second branch? I mean that except for the second branch tangent stiff, I'd like to define the displacement umax and when umax is reached than the uploading is done with the same tangent stiff.
Is it possible using the MinMax material?

Many thanks again!
Regards,
Olympia

[vesna]

MinMax material will not do what you need.

You can try to construct a Series material consisting of ElasticPP (histeretic or Steel01) and two ElasticPP Gap materials, one for compression and another for tension. With this combination of materials you will be able to catch the material response you want.

I would recommend you to test the Series material on a spring (zeroLength) element and then to apply it to the more complex model.

[Olympia]

Thank you very much vesna but I'm so confused...
A bearing constitutive law has not only a yielding point but also an ultimate point. How can I define the ultimate point using a series material?
I mean that in the case of time history analysis, if the input is too strong, the bearing has to fail after some cycles of loading but using the hardening or the series material it "works" for all the input duration. On the other hand if I use the MinMax material in order to define the ultimate displacement how the uploading will happen when this value is reached?

Thanks again,
Olympia

[vesna]

If you use MinMax material the stress (force) will go to 0 after the displacement limit is reached.

In the case of the series material I described above after reaching the ultimate value of displacement the unloading will depend on the stiffness of the material.

To understand better what each of the material commands does, make a truss or zeroLength element and assign to it different combination of materials.

[Olympia]

Dear vesna,

Unfortunately I don't understand how do it. I'd like to define a material with the following law:
[http://www.ruaumoko.co.nz/Gif/Loops/Loop01.GIF]
but all points have to defined (including uy and umax)
Could you please help me?
You could email me if you like, my email address is taskari@civil.auth.gr


Many thanks again,
Olympia

[vesna]

Dear Olymipia,

Sorry, but I misunderstood you. Unfortunately, there is no material with the capabilities you need in OpenSees. If you know some C++ you can code the material that you need.

Alternatively, there is a bearing element in OpenSees that you may consider using:
http://opensees.berkeley.edu/wiki/index ... ng_Element

[silvia]

the histeretic material goes horizontal after eps3.....

[vesna]

Sivia,

When I test the material I don't get what you say. After eps3 the force follows the slope defined by the line between points 2 and 3. It is horizontal only if sp2=sp3.

[silvia]

mmmm...... i'm not sure now, i remember it doing this....

[Olympia]

Dear vesna,

Thanks a lot again!! As I can understand by the parameters used to define the bearing element, again I can't limit the displacement of the bearing. I mean that there must be a limit in its deformation..

Thanks again,
Olympia

[silvia]

sigma3 has to be less than sigma2 then it goes flat after eps3