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Selim Hocam,
I think I am describing my problem wrong. I am trying define column elements that have different cross sectional dimensions and not aligned at the centroid of each cross section.

Please see this example sketch I created in this dropbox link:
https://www.dropbox.com/s/l75jdbop9lvjr ... s.pdf?dl=0

How can define those elements like the way they are aligned on one face of the columns and at their centroids?

Selim Hocam,

You mean I should shift the centroid of the fiber section and it should shift the element centroid? Just like this below?

set shiftYDir [expr 20.0]; # inches
set coverY [expr $HSec/2.0 - $shiftYDir];
set coverZ [expr $BSec/2.0];
patch quadr $IDconcU $nfZ $nfY -$coverY $coverZ -$coverY -$coverZ $coverY -$coverZ $coverY $coverZ;

Anybody knows how to do this? Selim Hocam, do you know?

Hi!
I have a quick question. Is there a way to define a section or element that is offset from the center line of the adjacent element? For example, if a 15 foot column with a block-out consists of 20x40 cross section for 10 feet, 20x20 for 3 feet but flushed on the face of the 20x40 section, and 20x40 for 2 feet, how can we provide that offset 20x20 section? How do we do that using fiber based elements and/or elastic line elements?
Thanks,
Baha

What is the error message?
It should work with the original example!
There may be some other scripts, search for "material test opensees" in the forum or google. There is many ways that you can test the material, the link I gave above is just an example.

Baha

These may help you:

https://opensees.berkeley.edu/wiki/inde ... l_Material

https://opensees.berkeley.edu/wiki/inde ... Aggregator

And you may test your material using, e.g., https://opensees.berkeley.edu/OpenSees/ ... al/751.htm

Regards,
Baha

You need to look at the diff equation of the Bouc-Wen model on the reference documents at the bottom of the page on the link you sent.
You can also test you material to see the effects different parameters; e.g., refer to https://opensees.berkeley.edu/OpenSees/ ... al/751.htm

The definition of yield strength and yield deformation in Bouc-Wen models is a bit different and are controlled by the parameters. Typically Bouc-Wen has smooth cyclic reversals and effective/equivalent yield strength and yield deformation. If you are trying to have sharp returns with explicit yield deformation & strength, you need to control that by the order (one of the parameters, typically shown as "n") in the equation. Again for that, refer to documents (& equations) and test your material, plot it and see what you defined.

Regards,
Baha

Hi,

I am wondering if there is a way to orient a fiber cross section and rotate it for a 2D problem? For example if I defined a fiber cross section, such as one of these fiber sections: http://opensees.berkeley.edu/wiki/index ... on_Example

Is there a way to rotate it 90 degrees so that the strong axis becomes weak-axis or vise-versa?

I know defining depth as width and width as depth is a way to do it, but I am just wondering if there is any easier way to just orient a section that has already been created.

Baha

I wonder if there is a way to simply assign masses to line elements (just using mass/length) without needing to create many nodes and assigning concentrated/lumped masses to each node?

Sincerely Yours,
Baha

Hi,

I have a quick question. Is there a problem with using initial strain (or stress) material and pushing it as displacement controlled?

I created a RC simple supported beam (4 point beam) with concrete and steel as initial strain material.
- For example, when I apply a loading two 10kips , I get about a deflection of 0.5in in the middle and reactions are 10 and 10 as expected and beam carries that load without any problem.
- But instead of applying those loads, if a create a load pattern and push the beam at two points with disp control in the middle of the beam, the support reactions never get close to 10kips but get to about 2.5kips max and beam middle deformation is more than 2in. I am not sure what's going wrong in the disp control.

I remember Vesna mentioning somewhere that initial strain or stress materials might have a problem with disp control, but I can't find that post. And using the force controlled push I can't get the strength of a material after it starts softening it can't carry the monotonically increasing load, which is due to force controlled pushover.

Anyone has an idea what might be going wrong? I really appreciate any idea.

Hello there,
Is there any example of a pre-stressed beam modeled in OpenSees?
Regards,

Yeah, though FFT peaks are cumulative measurements of time history. But I have been thinking if there is a way to see the mode shapes (therefore force distributions) instantaneously as the system goes through transitioning modal coordinates since every little change in the stiffness due to inelasticity will alter them. Still thinking if I can make sense of mode shapes obtained with tangent stiffness at each time step though.

Thank you for your reply.

I am actually thinking it as earthquake forces experienced by the building right at that step while building is going through different periods, rather than its damage implication.

It makes me think about the meaning of periods that "eigen" command give in each time step because the period is a phenomena for a cycle. But calculating many periods during an inelastic cycle, which continuously change every time step since stiffness keeps changing, makes things complicated b/c period keeps changing and reaching to very large values (3-4 times the initial T1). When I look at the response on the other hand, I see the corresponding cycle doesn't really have a period of 3-4 times of initial, but much smaller. Maybe the max period value obtained with the "eigen" in each time step doesn't make sense at all. Or average of those periods obtained with "eigen" should be corresponding to the period of that cycle?

Notwithstanding it is complicated, those eigen values should still be meaningful in terms of the frequency that the building experiences, right?

The eigen values I get with the "eigen" are not negative during an analysis I ran. I wonder if this is just by luck all positive or not?

Similarly I am getting eigen vectors using "nodeEigenvector" as normal values, wondering if this is similarly just by luck?

I have one more followup for the "eigen" or "nodeEigenvector" commands.

How do those commands calculate eigen values and vectors when the stiffness negative or, e.g. in the unloading branch?

Isn't there a complication of negative lambda values? I remember seeing in some posts that there may be negative eigen values obtained. Is there such a case when using "eigen" or "nodeEigenvector" commands? Frank was suggesting to use the last successful (non-negative) eigen values.