hi Husayn Mohammadi

Modeling shear links in Eccentric Braced Frame (EBF) systems can be quite complex due to the nonlinear and hysteretic behavior they exhibit during seismic events. OpenSees (Open System for Earthquake Engineering Simulation) and OpenSeesPy (the Python wrapper for OpenSees) are widely utilized for such modeling due to their comprehensive framework and the available elements which can depict nonlinear behaviors.

### Selecting Element Objects in OpenSees/OpenSeesPy:

When it comes to EBFs, researchers utilize various approaches for modeling, particularly in the context of shear links. Below are some elements and objects often used in OpenSees for this purpose:

- **ZeroLength Elements**: with material models that can capture the hysteretic behavior of the links.

- **ForceBeamColumn Element**: which allows for displacement interpolation along the element length and can account for P-Delta effects.

- **Material Models**: such as Steel02, which can replicate the hysteretic behavior of structural steel.

### Review of Papers:

1. **2018.05.22 - Silvia Caprili et al**:

A significant paper that attempts to tie experimental results with numerical ones. They might have used finite element models with calibrated parameters derived from experimental tests. Employing similar FEM models, especially those which use shell elements, can be computationally expensive and challenging.

2. **2016.06.02 - Mohebkhah et al**:

This paper, with a focus on displacement-based design, is likely to have dealt with an effective way to ensure performance-based design of EBFs. Learning from the models and approaches employed here could be very useful.

### Suggested Approach:

#### Modeling Considerations:

- **Hysteretic Behavior**: Ensure to model the hysteretic behavior of the shear link correctly by fitting your material model to experimental results.

- **Geometry**: EBFs may involve geometric non-linearities, especially with large displacements during seismic events. This needs to be considered in your model.

#### Step-by-Step General Guide using OpenSeesPy:

1. **Define Model Components**:

- Define nodes, materials, sections, and elements.

- For hysteretic behavior, explore various material models and choose the one fitting the experimental results.

2. **Apply Boundary Conditions**:

- Define supports and fixities at necessary nodes.

3. **Define Loading**:

- Define seismic loading based on the consideration of the study.

4. **Analysis Procedure**:

- Choose an analysis type suitable for seismic analyses, like transient analysis.

- Define convergence criteria based on energy or displacement.

- Run the analysis.

5. **Validation**:

- Ensure that your model is valid by comparing with available experimental results or existing validated models.

6. **Analysis**:

- Analyze the results in terms of displacements, member forces, and stresses.

- Ensure to check the hysteretic behavior under cyclic loading.

### Example and Additional Resources:

While crafting a specific example would be too extensive for this platform, many resources and examples are available online. The official OpenSees and OpenSeesPy websites, and forums contain numerous examples which can serve as a starting point. Research papers on similar topics can also be a great source to understand the modeling strategy followed by other researchers.

#### Final Note:

When it comes to shear links and EBFs, it's crucial to have a firm grasp of both the experimental and numerical perspectives to accurately model and validate the system’s behavior. Engaging in forums, consulting with experts in the field, and iterative modeling and validation are key to arriving at a reliable model. Always ensure to validate your numerical models with experimental results for credibility and reliability of predictions!

Hi Husayn Mohammadi

Modeling shear links in Eccentric Braced Frame (EBF) structures and replicating their hysteretic behavior accurately can indeed be challenging. However, OpenSees (Open System for Earthquake Engineering Simulation) and its Python wrapper, OpenSeesPy, provide quite extensive features and elements to model such behaviors.

### Recommended Element for Shear Links:

#### 1. **BeamWithHinges Element:**

- **Useful for Modeling**: BeamWithHinges can be used to model the link beams with plastic hinges at the ends and a linear elastic section in the middle.

- **Hysteretic Behavior**: This element allows for the modeling of different hysteretic behaviors using various material models available in OpenSees.

- **Applicability**: Especially apt for EBFs where the inelastic deformation is confined to the link beam.

#### 2. **ForceBeamColumn Element:**

- **Flexibility**: It allows you to specify fiber sections along the element length, enabling you to model the gradual yielding of the shear link.

- **Discretization**: You can discretize the shear link into multiple elements and define distinct properties for each section, which allows for a refined representation of expected behavior under lateral loading.

#### 3. **ZeroLength Element:**

- **Point-wise Behavior**: If you are more interested in the hysteretic behavior at a particular point (like a link-to-frame connection), ZeroLength elements with appropriate material and direction can be considered.

- **Utilization**: Using ZeroLength element with relevant hysteretic material models (e.g., Steel02, Hysteretic, etc.) to simulate the shear link behavior.

### Example:

Below is a generalized example of how you might use the BeamWithHinges element for shear link modeling. Please note that this is a conceptual representation, and you would need to fine-tune the model to accurately represent your physical shear links.

```python

import openseespy.opensees as ops

ops.wipe()

ops.model('basic', '-ndm', 2)

# Nodes and Fixities

ops.node(1, 0, 0); ops.fix(1, 1, 1)

ops.node(2, 5, 0); ops.fix(2, 1, 1)

ops.node(3, 5, 3)

ops.node(4, 0, 3)

# Materials

ops.uniaxialMaterial('Steel02', 1, 29000, 0.02, 20, 0.925, 0.15)

# Sections

ops.section('Elastic', 1, 29000, 300)

ops.section('Aggregator', 2, 1, 'P', 1, 'Mz') # P and Mz from Material #1

# Define Geometry and Element

ops.geomTransf('Linear', 1)

ops.element('forceBeamColumn', 1, 1, 4, 1, 1, '-iter', 10)

ops.element('beamWithHinges', 2, 2, 3, 5, 1, 1, 2, '-iter', 10)

# ...Further Modeling, Loads, and Analysis Commands

```

### Tips:

- **Calibration**: Ensure to calibrate your model by comparing with experimental results to check the validity of the element and material choices.

- **Literature Review**: Explore models in the papers and any supplementary materials or data they might have used.

- **OpenSees Community**: The OpenSees message board and community can be a good resource for specific advice on modeling in OpenSees.

Consider trying different elements and materials to evaluate which combinations best represent the physical and hysteretic behaviors of your shear links. And always validate the models against available experimental results for accuracy and reliability in predictions.

Thank you Mr. Yousef Bahrambeigi

I will apply the code you provided for me and if I had any questions I will bother you asking again.

Hi Husayn Mohammadi

According to the paper that attach in private massage the authors used a semi-analytical model for the quick representation of the cyclic behaviour of shear links. The model consists of a rigid beam element connected to two zero-length elements at the ends, which simulate the shear and flexural behaviour of the link, respectively. The zero-length elements are assigned different material models depending on the link type and geometry. For example, for a horizontal link with a rectangular cross-section, the authors used a bilinear material model for the shear behaviour and a Giuffré-Menegotto-Pinto model for the flexural behaviour.

Based on this description, I have generated an example code using openseespy that models a horizontal shear link with a rectangular cross-section. The code is not intended to be a complete or accurate representation of the experimental tests, but only a demonstration of how to use openseespy commands to create such a model. You may need to adjust the parameters and assumptions according to your specific case and objectives.

Here is the code:

python:

# Import openseespy module

import openseespy.opensees as ops

# Define model parameters

L = 1.0 # Link length (m)

b = 0.2 # Link width (m)

h = 0.1 # Link depth (m)

E = 210e9 # Elastic modulus (Pa)

G = 80e9 # Shear modulus (Pa)

fy = 355e6 # Yield stress (Pa)

b1 = 0.01 # Hardening ratio for shear

b2 = 0.02 # Hardening ratio for flexure

R0 = 18.0 # Parameter for Giuffré-Menegotto-Pinto model

cR1 = 0.925 # Parameter for Giuffré-Menegotto-Pinto model

cR2 = 0.15 # Parameter for Giuffré-Menegotto-Pinto model

# Create model

ops.wipe() # Clear previous model

ops.model('basic', '-ndm', 2, '-ndf', 3) # Define model dimension and degrees of freedom

# Create nodes

ops.node(1, 0.0, 0.0) # Node 1 at left end of link

ops.node(2, L, 0.0) # Node 2 at right end of link

ops.node(3, L/2, h/2) # Node 3 at center of link

# Define boundary conditions

ops.fix(1, 1, 1, 1) # Fix node 1 in all directions

ops.fix(2, 1, 1, 1) # Fix node 2 in all directions

# Define materials

ops.uniaxialMaterial('ElasticPP', 1, E*b*h/L, fy*b*h/L, b1) # Shear material with bilinear behaviour

ops.uniaxialMaterial('Steel02', 2, fy*b*h/6, E, b2, R0, cR1, cR2) # Flexural material with Giuffré-Menegotto-Pinto behaviour

# Define elements

ops.element('zeroLength', 1, 1, 3, '-mat', 1, '-dir', 2) # Zero-length element for shear behaviour at left end of link

ops.element('zeroLength', 2, 2, 3, '-mat', 1, '-dir', 2) # Zero-length element for shear behaviour at right end of link

ops.element('elasticBeamColumn', 3, 1, 3, A=b*h/6, E=E*b*h/6/Iz=Iy=b*h**3/12/Jx=b*h**3/12/G=G*b*h/6/L=L/2) # Elastic beam element for flexural behaviour at left half of link

ops.element('elasticBeamColumn', 4, 2, 3, A=b*h/6, E=E*b*h/6/Iz=Iy=b*h**3/12/Jx=b*h**3/12/G=G*b*h/6/L=L/2) # Elastic beam element for flexural behaviour at right half of link

# Define loads and analysis options

# You can define your own load pattern and analysis options here

you can search in this websites:

https://openseespydoc.readthedocs.io/en/latest/src/paralleltri31.html

https://opensees.berkeley.edu/wiki/index.php/Two_Node_Link_Element

https://opensees.berkeley.edu/OpenSees/manuals/ExamplesManual/HTML/876.htm

https://opensees.berkeley.edu/wiki/index.php/Examples_Manual

Be Successfully

Hi Yousef Bahrambeigi,

Your help is deeply appreciated. Wish you all the best too.