> For the complete documentation index, see [llms.txt](https://docs.openbrim.org/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.openbrim.org/templates/precast-i-girder-bridge-workflow/properties-pig/pushover-pig/hinge-property-pig.md).

# Hinge Property \[PIG]

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.![image-20251112-162944.png](https://openbrim.atlassian.net/wiki/download/attachments/2551808027/image-20251112-162944.png?api=v2)

## 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, the Moment Curvature Report should be directly assigned using the *From Report* column to extract hinge stiffness parameters.

**Hinge Stiffness:** If the user selects the option ‘User Input’ in the ‘Hinge Stiffness Option’ column, further definitions can be made using the ‘Hinge Stiffness’ column's ‘Open Table…’ 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 %}

## Linear

Transition along the axes (Tx, Ty, Tz) and rotation (Rx) can be determined for hinges. The definitions can be made either by numbers or by the option ‘Fixed'.

**Tx \[Fixed/Stiffness]:** Transition along X-axis.

**Ty \[Fixed/Stiffness]:** Transition along Y-axis.

**Tz \[Fixed/Stiffness]:** Transition along Z-axis.

**Rx \[Fixed/Stiffness]:** Rotation along X-axis.


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