Add Uniform Load

Uniform distributed loads can be applied to boundaries with the Add Uniform Load option.

Uniform distributed load

To apply a uniform distributed load:

1. Select Add Uniform Load from the toolbar or the Distributed Loads sub-menu of the Loading menu.

2. You will see the Add Distributed Load dialog. In this dialog:

• select the load orientation and enter the load magnitude

• in a multi-stage model, distributed loads can be staged by selecting the Stage Load checkbox, and entering a Factor for the load magnitude at each stage. If you do NOT stage the load on a multi-stage model, then the load will be applied with the same magnitude at all stages.

See below for details about the load magnitude, orientation and staging.

3. Select OK in the dialog, and you will be prompted to select the boundary line segment(s) on which to apply the load. Remember you can select Excavation, External, Material or Stage boundary segments. (You cannot apply distributed loads on Joint or Structural boundaries).

4. When finished selecting, press Enter or right-click and select Done Selection, and the distributed load will be applied to all selected segment(s), as indicated by the display of red arrows and the magnitude.

5. Check the direction of the arrows and the magnitude, to make sure that this is the load you wished to apply. If there is a mistake, you can repeat the above steps to apply the correct load, or use the Edit Distributed Load option to change the load parameters.

Load Magnitude

A distributed load magnitude is generally entered as a positive value. The direction of load application is specified by selecting an appropriate Orientation method (see below) in the Add Distributed Load dialog. If you enter a negative load magnitude this will reverse the direction of the applied load.

Load Orientation

The load orientation may be specified using one of the following options:

• Normal to Boundary – loads are applied normal to boundaries

• Vertical – loads are applied vertically (default = downward)

• Horizontal – loads are applied horizontally (default = to the right)

• Angle from Horizontal – specify an angle from the horizontal. Note that a POSITIVE angle is measured counter-clockwise from the positive X-axis direction.

• Angle to Boundary – specify an angle relative to the boundary on which the load is added.

• Field Stress Vector - the load applied will be equal in magnitude and opposite in direction to the field stress on the boundary (see Tutorial 24 - Tunnel Lining Design)

Flip Angle 180 degrees

NOTE: after adding a load, the orientation may sometimes be opposite from the intended direction (i.e. 180 degrees off). If this occurs, you can use the Edit Distributed Load option to "flip" (i.e. reverse) the load orientation by 180 degrees. See the Edit Distributed Load topic for information about editing distributed loads.

Staging Distributed Loads

On a multi-stage model, distributed loads can easily be staged by selecting the Stage Load checkbox in the Add Distributed Load dialog (Step 2 above), and selecting the Stage Factors button. You will see the Stage Factors dialog, in which you can enter a Factor for the load magnitude at each stage. NOTE:

• Factor = 1 means that the load magnitude will be equal to the magnitude(s) entered in the Add Distributed Load dialog.

• You can increase or decrease the load magnitude at any stage, by entering a Factor greater than or less than 1 (e.g. a Factor = 2 would double the load magnitude).

• You can remove the load at any stage, by entering a Factor = 0. The distributed load will not exist at any stage in which the Factor = 0, and will not appear on the model.

If your distributed load is staged, it is a good idea to select the Stage Tabs, after adding the load, to check that the load is applied at the correct stages, and that the magnitudes are correct. If not, then repeat Steps 1 to 5 (above) or use the Edit Distributed Loads option, and make sure that the correct Factors have been applied at the correct stages.

Note: the display of distributed loads (i.e. the red arrows) can be turned off in the Display Options dialog. Whenever you add or delete loads, all existing loads will be automatically displayed, even if they were turned off in Display Options.