RE; Recording Fx due to displacement Ux

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ryancwl95
Posts: 44
Joined: Mon Sep 25, 2023 12:42 am

RE; Recording Fx due to displacement Ux

Post by ryancwl95 » Sun Apr 07, 2024 3:30 pm

Hi,

I'm currently conducting a simulation where I laterally move a pile (only in the x-direction) in a sinusoidal prescribed pattern. In the initial analysis, I used a prescribed load and obtained the predicted displacement of the pile.

For the next analysis, I prescribed a displacement (obtained from the previous analysis) on the node rather than a prescribed load. I want to measure the amount of force required to move the pile by this displacement (ux). Additionally, I'm interested in tracking the development of the force Fx when the pile moves in a sinusoidal pattern.

Could someone please advise me on how to proceed with this ? What types of recorders would I need to collect the necessary data?

FYI, the prescribed load and displacement are given on one node in the pile region, with the rest of the nodes in the pile region tied to this master node.

Attached below is a screenshot of the model at the peak of the sinusoidal displacement.
Screenshot 2024-04-07 162150.png
Screenshot 2024-04-07 162150.png (258.58 KiB) Viewed 1408 times

Thank you in advance for your assistance.
Sincerely,
Ryan Chia

kesavapraba
Posts: 355
Joined: Sat Mar 28, 2020 2:25 pm

Re: RE; Recording Fx due to displacement Ux

Post by kesavapraba » Mon Apr 15, 2024 2:07 pm

Hi, I would suggest you to look at ForceFromReaction in STKO. This can help you to record the reacion developed at the location of constraints during the first stage of the analysis and subsequently apply it as force in the 2nd stage of the analysis. There is a discussion about how to apply the load in the link below.

viewtopic.php?f=33&t=1980
:: With best wishes ::
Prabakaran Kesavan

ryancwl95
Posts: 44
Joined: Mon Sep 25, 2023 12:42 am

Re: RE; Recording Fx due to displacement Ux

Post by ryancwl95 » Mon Apr 15, 2024 9:25 pm

Hello,

Thank you for your response.

I am currently using STKO solely for post-processing my results. I'm wondering if it's feasible to exclusively utilize element/node recorders to monitor the equivalent forces resulting from prescribed displacements at the nodes.

I attempted to use the recorder option "reactionForce" to extract the reaction forces data on the node situated at the edge of the pile. However, the obtained values do not align reasonably with the initial prescribed load analysis.

Is there a workaround for this issue? Any guidance or alternative approaches would be greatly appreciated.

Thank you.

kesavapraba
Posts: 355
Joined: Sat Mar 28, 2020 2:25 pm

Re: RE; Recording Fx due to displacement Ux

Post by kesavapraba » Wed Apr 17, 2024 1:24 pm

You can use reactions and nodeReaction commands from OpenSees to obtain nodal forces after an analysis step. Subsequently, apply the nodal forces using load pattern in your script. Please refer to the following link for more information.

https://portwooddigital.com/2021/11/15/ ... -reaction/
:: With best wishes ::
Prabakaran Kesavan

STKO Team
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Joined: Tue Oct 29, 2019 8:45 am

Re: RE; Recording Fx due to displacement Ux

Post by STKO Team » Mon Apr 29, 2024 8:18 am

If you apply an sp load (prescribed displacement) on a node, it's like a fixity... simply record the reaction (= force required to impose that displacement) on that same node

ryancwl95
Posts: 44
Joined: Mon Sep 25, 2023 12:42 am

Re: RE; Recording Fx due to displacement Ux

Post by ryancwl95 » Mon Jun 24, 2024 1:02 am

Hi
With respect to the same probelm, I have tried the links and suggestions given by kesavapraba and team STKO
kesavapraba wrote:
Wed Apr 17, 2024 1:24 pm
You can use reactions and nodeReaction commands from OpenSees to obtain nodal forces after an analysis step. Subsequently, apply the nodal forces using load pattern in your script. Please refer to the following link for more information.
https://portwooddigital.com/2021/11/15/ ... -reaction/
STKO Team wrote:
Mon Apr 29, 2024 8:18 am
If you apply an sp load (prescribed displacement) on a node, it's like a fixity... simply record the reaction (= force required to impose that displacement) on that same node
I am still unable to obtain the results i want. This query applies to a new scenario, I have a wished in place pile in a soil body, with the top of the pile subjected to a load of H0=1MN in X direction. At the centre of the pile are multiple nodes with close to 0 coordinates, and I have tied them all together in the XYZ direction with equalDOF command to represent the centre of the model (this is done throughout the z direction of the pile and the soil body). Additionally, I have tied all the nodes at the top surface of the pile to the master node (which i apply my load on) in the x direction. I initally applied a the load H0 for a transient analysis of 11s (increasing load with time). After which i have obtained a final ux displacement at the master node of 0.0033m.

Next, I started a new analysis, where I applied a prescribed load using the sp command of ux =0.0033m at the master node. I used the suggested methods (above) to monitor and record the reaction forces of that master node, hoping to get a reaction (RFx) of 1MN. But i only got a monitored value of 3.518kN. Below are some screen shots to help with he visualisation (master node 4571).
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Screenshot 2024-06-24 015517.png (72.39 KiB) Viewed 276 times
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Screenshot 2024-06-24 020011.png (12.28 KiB) Viewed 276 times

STKO Team
Posts: 2321
Joined: Tue Oct 29, 2019 8:45 am

Re: RE; Recording Fx due to displacement Ux

Post by STKO Team » Tue Jun 25, 2024 8:17 am

Why did you create several nodes overlapping?
When you attach them (slaves) to a master (on which you apply the imposed constraint) the reactions go on the slaves!
That's why you don't see the full reaction

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