How do I model an Eccentrically Braced Frame (EBF) in ETABS, including defining the shear link, assigning nonlinear hinge properties, and setting up loads for pushover or dynamic analysis?”
1. Draw the EBF Geometry: Use the frame drawing tools to create the columns, beams, and braces, placing the braces at an offset from the beam-column joints.
2. Define Sections and Materials: Assign your defined material properties and beam, column, and brace section properties. You will define a specific section for the shear link.
3. Model the Shear Link as a Specialized Element:
Create a separate beam section for the shear link, ensuring it has the appropriate geometry and material.
Assign a specialized frame element type for the shear link. In some versions of ETABS, this can be achieved by defining a link element.
2. Assign Nonlinear Hinge Properties
1. Define a User-Defined Hinge: In ETABS, navigate to Define > Hinge Properties. Create a new hinge property for the shear link.
2. Select the Hinge Type: Choose a hinge type that models the expected behavior of the shear link. For a shear link, this would typically be a "Shear Hinge".
3. Define the Hinge Backbone Curve: Input the backbone curve that represents the force-displacement relationship of the shear link. This includes the elastic stiffness, yield strength, and post-yield stiffness based on material testing or design specifications.
4. Assign the Hinge to the Link Element: Select the shear link elements in your ETABS model and assign the newly defined hinge property to them.
3. Set Up Loads for Analysis
Pushover Analysis:
Define Lateral Load Patterns: In ETABS, go to Define > Load Patterns. Create a new load pattern for your pushover analysis.
Apply Modal or Uniform Loading: Select a load distribution based on the first mode of vibration, a uniform distribution, or a combination.
Define the Pushover Analysis Parameters: Specify the base of the structure, the control node (e.g., the roof level), and the analysis type.
Dynamic Analysis (Nonlinear Time History Analysis):
Define Ground Motions: In ETABS, go to Define > Ground Motions. Import the relevant earthquake records or define them using velocity, acceleration, or displacement data.
Create Response Spectrum or Time History Load Cases: Define load cases that apply the defined ground motions to the structure. For nonlinear time history analysis, you will need to define a nonlinear time history load case.
Assign Loads to Elements: Assign the defined ground motions to the structure.
4. Run the Analysis
Perform the Analysis: Execute the analysis in ETABS.
Evaluate Results: Analyze the results for inter-story drift, hinge rotation, and overall performance to assess the structure's seismic behavior.