Gap simualtion

[Lei Lei]

Thanks for your reply!

Since there are only parameters about the normal and tangential penalty and mu, the zerolengthcontact element couldn't correctly show the nonlinear behavior of the joint.

Considering the zerolengthsection element can be defined with a section and different materials at different positions, I think using this element is more appropriate to simulate the behavior of the gap. Just like in Figure1

In fact, the two beams are connected by two steel bolts at the gap. So it's a really complex simulation.

Best wishes!

[Lei Lei]

Dear STKOteam,

I used the zerolengthsection element to simulate the joint in the middle of the beam.

When I applied displacement at loading points, it would output a plausible result, while its results were obviously wrong when I applied nodeforce at the same locations. What's the reason of it?

The units I used are N，mm，s

Looking forward to your reply!
Best wishes!

[kesavapraba]

Hi, I am not sure about the specific application of the loading (displacement/force) in your work. However, It is important to note that variations may arise depending on the reference load while doing displacement control analysis. I recommend aligning your loading methodology with that used in the experimental procedure for consistency.

[Lei Lei]

hello.

In fact, in my experiment, I applied both vertical and horizontal forces.

Given the complex behavior of the joints, I just apply vertical loads first.

However, the results were very strange. So I tried to use the final deformation as the target load, and the results looked good.

Whether to adjust the settings for the two different loading modes？

Best wishes!

[kesavapraba]

Ok, It is fine as long as the location of displacement is same as the load. Please check if the displacement has horizontal displacement component as well, because you say both vertical and horizontal loads have been applied on the specimen. Such loading can lead to resultant displacement, which may not align along the vertical direction only. If it exists, you should ensure that two components of the displacement are applied.

[Lei Lei]

Hi，
For two different models, I only applied the vertical values.

A result with only vertical displacement is more appropriate than a result with only vertical nodal forces.

The vertical load values of both models will guarantee that the beams will not be destroyed. However, the model deformation pattern caused by vertical force loading is strange and different from the result of vertical displacement loading.

In my opinion, the results of both models should be similar and the magnitude of response should be the same. Will there be such a big difference in the results of the model between the two different loading methods? Is there anything I need to adjust to the model settings for different loading methods?

Looking forward to your reply！

[kesavapraba]

Given every other settings identical, there should not be any difference if the locations of the displacement and load are the same. You can send us those two models for review.

[Lei Lei]

Dear STKOteam,

The difference between the two models may be due to the lack of shear resistance of the joint. As a result, the calculation error of the joint is too large and the deformation is too large when the vertical force is applied.

Therefore, I used an 'aggregator' to give shear resistance to the joint, but I reported errors. However, the results from using the recorder output seem reasonable.

It can compute successfully when I forgive using the 'MPCORecorder' command.

What's the reason for it? The version of STKO is 3.3.0 and of Opensees solver is 3.4.0.

Looking forward to your reply!

[kesavapraba]

Analysis results are not dependent on the recorder type. The error should be related to the specific recorder type. New versions of OpenSees come with many updates, so there can be some inconsistency. Unless if we do not have the specific error message, it is challenging to identify the cause of the error.

[STKO Team]

The issue with your model, when you apply forces, is that is is singular.
When you apply a fiber section to a zeroLengthSection element, it will only resist P-My-Mz-T modes.
The two shear modes Vy and Vz are un-constrained!

I simply put the fiber section (P-My-Mz-T) into a section aggregator (using stiff materials, but you can use any uniaxial material you want) for Vy and Vz.
To record strain and stress in a fiber section inside an aggrator, I also added custom results section.section.fiber.strain and section.section.fiber.stress (you need 2 section keywords: the first for the aggregator and the second for the fibersection)

Finally, I use a displacement control and a more strict test tolerance