[StructuralMechanicsApplication] semi-rigid hinge at 3d2n linear beam by aronnoordam · Pull Request #12290 · KratosMultiphysics/Kratos

aronnoordam · 2024-04-18T13:42:27Z

added semi rigid hinge to linear 3d2n beam element

according to:

[simões 1996] https://www.sciencedirect.com/science/article/abs/pii/0045794995004270,

philbucher · 2024-04-19T17:16:59Z

Can you please briefly explain what this does? I dont have access to the paper

aronnoordam · 2024-04-22T07:06:25Z

@philbucher using the matrix as described in the paper, a hinge with a rotational stiffness can be added to a beam element. where 0 stiffness corresponds to a normal hinge; infinite stiffness corresponds to a normal connection (as it was before).

using the rotational stiffnesses fixity factors for both sides of the beam are calculated ranging from 0 to 1. The resulting matrix (for euler beams) will be:

where alpha1 and alpha2 are the fixity factors

aronnoordam · 2024-04-22T07:09:24Z

fyi, I need this in order to simulate rail joints which have e.g. 90% of the stiffness of the rail itself

philbucher · 2024-04-24T11:33:29Z

...ructuralMechanicsApplication/tests/beam_test/semi_rigid_linear_3D2NBeamCr_test_material.json

+                "I33"               : 1e-5,
+                "SEMI_RIGID_ROTATIONAL_STIFFNESS_VECTOR_AXIS_2": [0e0],
+                "SEMI_RIGID_ROTATIONAL_STIFFNESS_VECTOR_AXIS_3": [1e7],
+                "SEMI_RIGID_NODE_IDS": [6]


I am pretty hesitant using IDs as input because they are reordered in MPI

How about using Nodal-Data to specify this?

that makes sense. I've changed it

philbucher · 2024-04-24T11:57:38Z

applications/StructuralMechanicsApplication/custom_elements/cr_beam_element_linear_3D2N.cpp

+{
+    KRATOS_TRY
+
+    if (this->GetProperties().Has(SEMI_RIGID_NODE_IDS)) {


in a restart, should this be done every time?

I guess not no?

this cannot be done anymore, as the check for semi-rigidity cannot be done in Initialize anymore, since there is the possibility that the rotational stiffness is not assigned yet (depending on the order of the proces executions

philbucher · 2024-04-24T11:57:57Z

applications/StructuralMechanicsApplication/custom_elements/cr_beam_element_linear_3D2N.cpp

+        KRATOS_ERROR_IF_NOT(this->GetProperties().Has(SEMI_RIGID_ROTATIONAL_STIFFNESS_VECTOR_AXIS_2)) << 
+            "SEMI_RIGID_ROTATIONAL_STIFFNESS_VECTOR_AXIS_2 must be set when SEMI_RIGID_NODE_IDS is used\n";
+        KRATOS_ERROR_IF_NOT(this->GetProperties().Has(SEMI_RIGID_ROTATIONAL_STIFFNESS_VECTOR_AXIS_3)) << 
+            "SEMI_RIGID_ROTATIONAL_STIFFNESS_VECTOR_AXIS_3 must be set when SEMI_RIGID_NODE_IDS is used\n";
+        KRATOS_ERROR_IF_NOT(this->GetProperties()[SEMI_RIGID_NODE_IDS].size() == this->GetProperties()[SEMI_RIGID_ROTATIONAL_STIFFNESS_VECTOR_AXIS_2].size()) << 
+            "SEMI_RIGID_ROTATIONAL_STIFFNESS_VECTOR_AXIS_2 must have equal size as SEMI_RIGID_NODE_IDS\n";
+        KRATOS_ERROR_IF_NOT(this->GetProperties()[SEMI_RIGID_NODE_IDS].size() == this->GetProperties()[SEMI_RIGID_ROTATIONAL_STIFFNESS_VECTOR_AXIS_3].size()) <<
+            "SEMI_RIGID_ROTATIONAL_STIFFNESS_VECTOR_AXIS_3 must have equal size as SEMI_RIGID_NODE_IDS\n";


I think it would make sense to move this to the Check function

philbucher · 2024-04-24T12:00:30Z

applications/StructuralMechanicsApplication/custom_elements/cr_beam_element_linear_3D2N.cpp

+            "SEMI_RIGID_ROTATIONAL_STIFFNESS_VECTOR_AXIS_3 must have equal size as SEMI_RIGID_NODE_IDS\n";
+
+        // create integer list
+        Vector semi_rigid_node_id_input = this->GetProperties()[SEMI_RIGID_NODE_IDS];


Here is an example of using the nodal data for specifying the input:

Kratos/applications/StructuralMechanicsApplication/custom_elements/spring_damper_element.cpp

Line 468 in d4a91c0

const array_1d<double, 3>& nodal_stiffness = this->GetValue(NODAL_DISPLACEMENT_STIFFNESS);

This way you can be sure that the correct nodes have the input
Additionally, for large number of hinges it will it overcrowd your materials.json

philbucher

minor remaining comments, otherwise good to me 👍

philbucher · 2024-04-26T10:01:32Z

...cturalMechanicsApplication/tests/beam_test/semi_rigid_linear_3D2NBeamCr_test_parameters.json

+        "Parameters"            : {
+            "mesh_id"         : 0,
+            "model_part_name" : "Structure.Parts_semi_rigid_hinge",
+            "variable_name"   : "ROTATIONAL_STIFFNESS_AXIS_3",


FYI you can directly write this in the mdpa, up to you

Kratos/kratos/tests/auxiliar_files_for_python_unittest/mdpa_files/test_model_part_io_read.mdpa

Lines 73 to 78 in e2ec331

Begin NodalData BOUNDARY

1

2

973

974

End NodalData

philbucher · 2024-04-26T10:03:15Z

applications/StructuralMechanicsApplication/structural_mechanics_application_variables.cpp

+KRATOS_CREATE_VARIABLE(double, ROTATIONAL_STIFFNESS_AXIS_2)
+KRATOS_CREATE_VARIABLE(double, ROTATIONAL_STIFFNESS_AXIS_3)


just to confirm, those are actual stiffnesses and not bools to enable/disable the hinge?
And they are nodal quantities, not elemental?

yes thats correct, its the rotational nodal stiffness in the local direction of the beam

philbucher · 2024-04-26T10:03:39Z

applications/StructuralMechanicsApplication/custom_elements/cr_beam_element_linear_3D2N.hpp


 private:

+    void CalculateRigidityReductionMatrix(


Please add a brief description what this method does

philbucher · 2024-04-26T10:06:11Z

applications/StructuralMechanicsApplication/custom_elements/cr_beam_element_linear_3D2N.cpp

+    // set fixity factors, 0 is no fixity, i.e. a hinge; 1 is completely fixed, the resulting stiffness matrix will remain unchanged
+    if (r_geometry[0].Has(ROTATIONAL_STIFFNESS_AXIS_2)) {
+        const double rotational_stiffness_y_1 = r_geometry[0].GetValue(ROTATIONAL_STIFFNESS_AXIS_2);
+        alpha1_zz = (rotational_stiffness_y_1 > 0) ? 1 / (1 + 3 * E * Iy / (rotational_stiffness_y_1 * L)) : 0.0;


if those must be larger than 0 if defined, then this should be checked in Check. Then you can simplify the logic here

it is also allowed to be 0, this means that a normal hinge is simulated. In that case, this if statement is still required, else there is a division by 0. I will add a check to check if its lower than 0, because this is not allowed

philbucher · 2024-04-26T10:07:47Z

applications/StructuralMechanicsApplication/custom_elements/cr_beam_element_linear_3D2N.cpp

+    if (r_geometry[0].Has(ROTATIONAL_STIFFNESS_AXIS_2)) {
+        const double rotational_stiffness_y_1 = r_geometry[0].GetValue(ROTATIONAL_STIFFNESS_AXIS_2);
+        alpha1_zz = (rotational_stiffness_y_1 > 0) ? 1 / (1 + 3 * E * Iy / (rotational_stiffness_y_1 * L)) : 0.0;
+    }


you can skip the Has check. If you make sure that they have a valid input, and the Geometry from which you get the nodes from is const, then you can simplify to
const double alpha1_zz = 1 / (1 + 3 * E * Iy / (r_geometry[0].GetValue(ROTATIONAL_STIFFNESS_AXIS_2) * L))

In order to not have a change of behaviour of the existing beam, the default beam should be without hinge. This means that the default ROTATIONAL_STIFFNESS_AXIS_2 should be infinite. In my oppinion it is cleaner to do a check if the ROTATIONAL_STIFFNESS_AXIS_2 is actually defined, thus keeping the Has.

philbucher

Nice 👍

aronnoordam · 2024-04-29T08:38:37Z

Nice 👍

Thanks :D, however I did not commit the Check and the brief discription yet, I've done that now in the latest commit

philbucher

👍

RiccardoRossi

Hi,

Aside for the comments of @AlejandroCornejo , i think this shoukd be handled element by element and not node by node.

Furthermkre i would suggwst to do bithacking, so that for exampke
100000100000

Means releasing the x displacmeent component of the two ends of the beam

aronnoordam added 3 commits April 18, 2024 15:38

initial commit semi rigid hinge at 3d2n beam

a621969

corrected stiffness reduction matrix in linear 3d2n beam

6c21691

corrected stiffness reduction matrix in linear 3d2n beam

a69a73b

aronnoordam added 5 commits April 23, 2024 11:54

corrected test semi rigid beam

7bd6e0b

style

f5cb5b4

style

39e9611

added test to suite

378374d

changed test such that it tests semi-rigidity

880c178

aronnoordam marked this pull request as ready for review April 24, 2024 11:20

aronnoordam requested a review from a team as a code owner April 24, 2024 11:20

philbucher reviewed Apr 24, 2024

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aronnoordam added 4 commits April 24, 2024 17:01

removed reference to node ids

e3d5f9d

reverted removal of serializer

06affb5

style

0f86b2d

style

71e586e

aronnoordam requested a review from philbucher April 25, 2024 08:04

philbucher reviewed Apr 26, 2024

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philbucher previously approved these changes Apr 29, 2024

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added check for ROTATIONAL_STIFFNESS around axis 2 and 3

ae3107b

aronnoordam dismissed philbucher’s stale review via ae3107b April 29, 2024 08:33

aronnoordam enabled auto-merge April 29, 2024 08:37

aronnoordam requested a review from philbucher May 1, 2024 06:55

philbucher approved these changes May 2, 2024

View reviewed changes

aronnoordam merged commit 14a13cb into master May 2, 2024

aronnoordam deleted the hinge_at_beam branch May 2, 2024 15:22

aronnoordam mentioned this pull request Jan 7, 2026

[StructuralMechanicsApplication] Inconsistency mass matrix cr_beam_element_2d2n and cr_beam_element_3d2n #14096

Open

RiccardoRossi reviewed Feb 25, 2026

View reviewed changes

		KRATOS_CREATE_VARIABLE(double, ROTATIONAL_STIFFNESS_AXIS_2)
		KRATOS_CREATE_VARIABLE(double, ROTATIONAL_STIFFNESS_AXIS_3)

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