# Add Polygonal Load

A general polygonal load can be defined with the **Add Polygonal Load** option. The load magnitude can be uniform or variable, and the load application can be staged.

To add a polygonal load:

- Select
**Add Polygonal Load**from the toolbar or the**Loads**menu. - In the Plan View, enter the vertices of the polygon as described in Entering Coordinates.
- A load polygon must be closed. To close the polygon boundary, after all vertices are entered, right-click and select
**Close**, or you can type**c**and Enter in the prompt line. This automatically and correctly closes the polygon, and saves you the trouble of having to re-enter the first vertex to complete the boundary. If the Snap option is activated, you can also close a polygon by snapping to the first vertex after all other vertices are entered. - After the polygon is closed, you will see the
**Define Load**dialog for polygonal loads. Enter the following information: - Load Name
- Load Properties (magnitude, direction, depth / bottom elevation, staging information, load type)
- Display Properties (optional)

- When you are finished entering the load information, select OK. The load will be added to the model, and displayed in both the Plan View and 3D View.

See below for details about the input parameters.

*Polygonal loads in 3D view*

The parameters which define a polygonal load are described below.

## Load Type

For a polygonal load, you may choose **Load Type** = **Flexible** or **Rigid**.

__Flexible__

For a Flexible load you can define the load magnitude as a uniform or variable Pressure. A Flexible load implies that the stress distribution on the ground immediately beneath the load is equal to the loading stress distribution.

__Rigid__

For a Rigid load, you can define the load magnitude as a uniform or variable Pressure, or as a Force and two Moments. A Rigid load implies that the displacement immediately beneath the load remains planar. The stress distribution immediately beneath the load is not (in general) equal to the loading stress distribution, due to the rigid displacement constraint.

NOTE: rigid loads cannot be used with time-dependent consolidation analysis in *Settle3*, only with immediate elastic settlement or long term consolidation.

See the *Settle3* Theory Manual for further information.

## Load Direction

If the **Boussinesq** or **Westergaard** stress computation methods are selected, and the load type is defined as **Flexible**, then the following load direction options are available:

- Vertical
- Horizontal
- Vertical and Horizontal

If any of the other stress computation methods are selected, or the load type is set to Rigid, only vertical loads can be defined.

## Load Magnitude

Load magnitude is defined in terms of force / area (i.e. distributed load or pressure). The pressure can be uniform or variable. For rigid loads you also have the option of defining the load magnitude as a Force and two Moments.

__Uniform Pressure__

To define a uniform load magnitude, enter the pressure (force per unit area) in the **Pressure** edit box. This will define a load with a uniform magnitude over the area of the polygon.

__Variable Pressure__

To define a load magnitude which varies over the area of the polygon, select the **Variable** checkbox and select the **Define** button. You will see a dialog which allows you to define the load magnitude at each vertex of the polygon.

NOTE: the load magnitude at each vertex is defined as a **distributed** **load** (i.e. force / area). You are NOT defining point loads, you are defining the magnitude of the distributed load, at each vertex. It is up to the user to determine the appropriate magnitude at each point, which correctly models the desired load distribution.

The load distribution over the area of the polygon is obtained by interpolation using the load magnitudes at the vertices.

*Variable load magnitude over a polygonal area*

__Force and Moments__

For Rigid loads you can define the load magnitude as a single vertical Force and two Moments (Mx and My) with x and y axes. The force is applied through the centroid of the load. If you apply moments, the settlement under the load will not be horizontal, but will follow an inclined planar function.

If your model uses multiple stages, the load can be applied at any stage, or applied in increments at different stages, as described in the Load Staging section below.

__Horizontal Loads__

In defining a horizontal flexible load, the same options exist as for a flexible vertical load. The **Angle from X axis** can also be defined for a horizontal load. The **Angle** is defined as the counter-clockwise angle between the X-axis and the direction of the horizontal load.

## Load Depth

A load can be applied on the ground surface or at any depth below the ground surface.

__Horizontal Soil Layers__

If the Horizontal Soil Layers option is selected in the Soil Profiles tab of the Project Settings:

- If the vertical axis is defined as
**Depth below Ground Surface**, the load depth is defined by**Depth**. - If the vertical axis is defined as
**Elevation**with a Ground Elevation specified, the load depth is defined by**Bottom Elevation**. The default elevation is that specified in the Project Settings.

__Non-Horizontal Soil Layers__

If the Non-Horizontal Soil Layers option is selected in the Project Settings, and the Non-Horizontal Ground Surface option is NOT selected, then the load depth / elevation is defined in the same way as when the Horizontal Soil Layers option is selected.

If the Non-Horizontal Soil Layers and the Non-Horizontal Ground Surface options are selected, the load depth is defined by **Bottom Elevation**. The default elevation is that specified in the Project Settings.

If your model uses multiple stages, the depth of the load can be staged, as described below.

NOTE: if you apply a load at some depth below the ground surface, the soil above the load depth is NOT assumed to be excavated, it is assumed that the soil layers remain in place. If you wish to define loading within an excavation, then you must use the **Add Excavation** option to define an excavation, and then define the loading. See the Add Excavation topic for details.

## Load Staging

If your model uses multiple stages, the load can be applied at any stage, or applied in increments at different stages using the Advanced Staging option.

__Installation Stage__

If you wish to apply a load at a particular stage of a multi-stage model, then use the **Installation Stage** option to select the desired Installation Stage.

__Advanced Staging__

For more complex load staging, the **Advanced Staging** option allows you to stage the magnitude and depth of the loading. To use the Advanced Staging option:

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