How to extract the element force in fiber section

Hello! In this section we'll talk about the post processing module and the data visualization.
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qutyjsxx
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Joined: Tue May 17, 2022 1:48 pm

How to extract the element force in fiber section

Post by qutyjsxx » Fri May 20, 2022 3:37 am

Dear STKO Team,
I study the hysteretic behavior of bridge piers by applying axial static and horizontal cyclic loads. I checked element force in the Recorder, but I don't know how to extract the horizontal force applied to the bridge pier in the post-processing interface. Please help me, thank you!
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STKO Team
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Re: How to extract the element force in fiber section

Post by STKO Team » Mon May 23, 2022 7:53 am

You cannot extract results on element nodes (like force or localForce) in the ExtractChartData tool. But you can extract section.force (in the Gauss Plot). If you are using a standard Lobatto Integration, the first and last integration points are always on the element's end-nodes. Just pay attantion because they are in local coordinate systems.

Otherwise, in your specific case, you can simply extract the base reaction under each pier

STKO Team
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Re: How to extract the element force in fiber section

Post by STKO Team » Mon May 23, 2022 8:21 am

Alternatively, if you really need a result from element nodes, you can use our Python API.
It is a powerful tool that allows you to do whatever you want.

Here's a simple script you can use for this. Just change the element_id (you can see your element ID using the Labels in the mesh visualization of the preprocessor), and the node_local_id (the 0-based index of the element nodes. for a 2-nodes beam it's always 0 for the first node, or 1 for the last node)
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cqf_2232
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Re: How to extract the element force in fiber section

Post by cqf_2232 » Fri May 27, 2022 8:24 am

Dear STKO Team,
I read the above Q&A. I haven't learned Python, so I don't understand the code very well. When I modify the code to extract the element force (Fz) from my model, it prompts me that there is no element force data, why is this?
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STKO Team
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Re: How to extract the element force in fiber section

Post by STKO Team » Fri May 27, 2022 8:59 am

It's because of this line (9):

Code: Select all

# get result (gobal force at element end-nodes)
result = db.getElementalResult('force', match=MpcOdb.Contains)
It is basically saying "pick the first elemental results whose name contains the string 'force'"

But in your case, you have 3 results of type force. For the beam you need those with 6 components.
So you can change the above code with:

Code: Select all

# get result (gobal force at element end-nodes)
result = db.getElementalResult('force (6', match=MpcOdb.Contains)
Let me know if it works

cqf_2232
Posts: 64
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Re: How to extract the element force in fiber section

Post by cqf_2232 » Fri May 27, 2022 12:19 pm

Thank you very much, I successfully extracted the element force. But I found a wonderful thing, the element force and the pseudo time are consistent, why is this?
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STKO Team
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Re: How to extract the element force in fiber section

Post by STKO Team » Mon May 30, 2022 2:07 pm

It's because you are asking the force on the top of the beam, which is the same point of application of the unit lateral force.

This unit force is multiplied by the loadFactor computed by the displacement control analysis. In the displacement-control analysis the pseudo time is actually the loadMultipler (if you are using a Linear timeSeries from 0-to-1).

The total force on the beam top should be
F = Lambda(pseudoTime) * ReferenceLoad

But you are using a Linear time series (X ranges from 0 to 1, and Y ranges from 0 to 1, so it's like X = Y), so:
Lambda(pseudoTime) = pseudoTime

So
F = pseudoTime * ReferenceLoad

But the reference load is 1, so:
F = pseudoTime * 1 = pseudoTime

qutyjsxx
Posts: 3
Joined: Tue May 17, 2022 1:48 pm

Re: How to extract the element force in fiber section

Post by qutyjsxx » Fri Jun 17, 2022 2:19 am

Dear STKO Team,
At present, I have built two nodes at the same position in STKO, and they are connected by node to node links. I want to assign the BondSP01 material to the Zero-length section element to simulate bond slip. How to implement it in STKO, can you give a simple example?
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STKO Team
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Re: How to extract the element force in fiber section

Post by STKO Team » Tue Jun 21, 2022 3:52 pm

Dear STKO Team,
At present, I have built two nodes at the same position in STKO, and they are connected by node to node links. I want to assign the BondSP01 material to the Zero-length section element to simulate bond slip. How to implement it in STKO, can you give a simple example?
1) Create a Fiber Section (physical property) with the BondSP01 as steel
2) Create a zeroLengthSection (element property)
3) Assign them to the interaction

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