Some questions regarding FP isolator material

[Samyog]

Hello all,

I am trying to understand FP isolator material model in MASTODON. I am not being able to understand why there is "N * local_rotation" terms in the formulation of shear force (Lines 380, 381, 410, 412) for FP isolator and not for LR isolator. 

Also I do not understand how plastic displacement is same as dGamma (Lines 402, 403, 406, 407)?

Thank you

Samyog

[Sai Sharath Parsi]

Hi Samyog,

1. In the single FP bearing, we have an articulated slider that rotates as it slides on the curved surface. This changes the equilibrium conditions in the horizontal and vertical direction. Also, please note that the horizontal force depends on the vertical load in the FP bearing which is not the case for the LR bearing. I encourage you to read pages 52-54 of the report below. We can discuss further if needed.

http://www.eng.buffalo.edu/mceer-reports/15/15-0006.pdf  

2. I don't think I am able to understand your second question. I see the expressions for dGamma (lines 403 and 404) and ubPlastic (lines 407 and 408) are different. Could you please elaborate?

Regards

Sharath

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Sai Sharath Parsi

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Department of Civil, Structural and Environmental Engineering

University of Buffalo

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[Samyog]

Hi Sharath,

1. Looking at Eq 4-4 in the report, F = S / cos (theta) + W / sqrt (R^2 - u^2) * u. From here, if theta ~ 0 and W ~ N, it follows that Fby = qYield + k2y * disp_basicy and similar in other shear direction. Instead of qYield, I guess there is qYield * qTrialy / qTrialnorm to account for bidirectional effect. In this equation, there is no rotation term, but I suppose the model in MASTODON is not making those simplifications (theta ~ 0 and W ~ N)? Additionally, in Fig 4.3 (b), the top plate is shown horizontal, does it mean rotation at the top of this FP isolator element must be restrained (for any analysis using this material) so that the relative rotation (theta) is equal to the rotation of bottom node?

2. Assuming shear displacement only in one direction, ubplastic = ubplastic_old + dGamma because qTrial = qTrialnorm. Is there any plot that shows exactly what ubplastic and dGamma are?

Thank you

Samyog

On Monday, August 17, 2020 at 12:28:03 PM UTC-4, Sai Sharath Parsi wrote:

Hi Samyog,

1. In the single FP bearing, we have an articulated slider that rotates as it slides on the curved surface. This changes the equilibrium conditions in the horizontal and vertical direction. Also, please note that the horizontal force depends on the vertical load in the FP bearing which is not the case for the LR bearing. I encourage you to read pages 52-54 of the report below. We can discuss further if needed.

http://www.eng.buffalo.edu/mceer-reports/15/15-0006.pdf  

2. I don't think I am able to understand your second question. I see the expressions for dGamma (lines 403 and 404) and ubPlastic (lines 407 and 408) are different. Could you please elaborate?

Regards

Sharath

On Sun, Aug 16, 2020 at 11:35 PM Samyog <samy...@gmail.com> wrote:

Hello all,

I am trying to understand FP isolator material model in MASTODON. I am not being able to understand why there is "N * local_rotation" terms in the formulation of shear force (Lines 380, 381, 410, 412) for FP isolator and not for LR isolator. 

Also I do not understand how plastic displacement is same as dGamma (Lines 402, 403, 406, 407)?

Thank you

Samyog

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https://mooseframework.org/mastodon
https://github.com/idaholab/mastodon
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