# Hinge Property \[SIG]
Hinges represent points in the structural model where **plastic deformation** is expected to occur under **seismic loads**. They are essential for **nonlinear pushover analysis** to capture the inelastic behavior of pier columns. It can be assigned to columns as shown below, at both the top and bottom locations.
## Nonlinear
**Hinge Stiffness Option \[From Report/User Input]:** The user can define how the hinge stiffness is determined:
* **From Report:** The hinge stiffness is automatically derived from the **Moment-Curvature Report**.
* **User Input:** The user directly specifies hinge stiffness values for each axial force.
**Moment Curvature Report:** If "From Report" is selected in the Hinge Stiffness Option, you can assign a Moment Curvature Report to automatically derive hinge stiffness parameters. Follow these steps:
1. First, create and configure a [Moment-Curvature Report](/templates/steel-i-girder-bridge-workflow/properties-sig/pushover-sig/moment-curvature-report-sig.md) with appropriate section geometry, materials, and axial forces.
2. In the Moment-Curvature Report, go to the Output tab and use the "Compute" cell action to generate the analysis results.
3. Return to this Hinge Property and select the computed Moment Curvature Report from the dropdown in this parameter.
4. The hinge stiffness values (Ry and Rz) will be automatically extracted from the report for all specified axial force levels.
{% hint style="warning" %}
The Moment-Curvature Report must have its output computed before it can be assigned here. If the report is not computed, the hinge will not have valid stiffness data and analysis may fail. See [Moment-Curvature Report - Output Tab](/templates/steel-i-girder-bridge-workflow/properties-sig/pushover-sig/moment-curvature-report-sig.md#output) for instructions on computing the report.
{% endhint %}
**Hinge Stiffness:** If the user selects the option ‘Set to User Input’ in the ‘Hinge Stiffness Option’ column, further definitions can be made using the ‘Hinge Stiffness’ column's ‘Edit…’ option, detailed by **Axial Force/Fixity (Ry)/Fixity (Rz)**. When defining hinge stiffness data, make sure to include a sufficient number of axial force data points around the expected dead load level.
Define hinge stiffness data with enough axial force points around the expected dead load for stable nonlinear convergence.
Use intervals of about **50 kips** near the maximum load.
**Example:** For a –750 kip dead load, enter values such as **250, 0, –50, –100, … –1000 kips**.
**Positive values** indicate **tension**, and **negative values** indicate **compression** - both are required for accurate nonlinear analysis.
{% hint style="info" %}
The **column section**, **Moment Curvature Report section**, and **column rotation angle** must all be **consistent** with each other to ensure that the hinge stiffness and rotational axes (**Ry**, **Rz**) correctly represent the actual behavior of the column.
{% endhint %}
Coordinate System for the Report
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