How to extract the element force in fiber section

[qutyjsxx]

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!

[STKO Team]

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]

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)

make_chart_ele_nodal_results.zip

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extract ele force.png (194.84 KiB) Viewed 1473 times

[cqf_2232]

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?

[STKO Team]

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]

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?

[STKO Team]

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]

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?

[STKO Team]

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