Differential settlements

In this exercise, we will see how to measure differential settlement from a polyline using the method described by API 653. The polyline must represent the edge between the shell and the bottom plate of the tank.

Show only “Tank mesh 1”. Select the polyline “Tank mesh 1 Contour bottom” in the “Separate shell” folder and launch Differential Settlements.

You can choose to use the tolerances defined in the API 653 by checking the very first option.

The Orientation Marker defined when creating the project is used by default as the start point. You can define a new point if needed.

Then, set how many points are needed to measure the settlement. The default number of points (8 here) is the minimum number requested by the standard. Enter 50 for the number of points. The points are automatically created on the polyline in the 3D preview and the computation is automatically done.

The results are displayed in the dialog box. A table is showing the results in each point:

• Elevation: the elevation of the point,

• Tilt plane elevation: the value in the best cosine curve at the index of the point,

• Magnitude of the differential settlement (Ui): the difference between the elevation and the tilt plane elevation of the point,

• Deviation (Si): Si = Ui - (1/2Ui-1 + 1/2Ui+1)

It is possible to use the Elevation Marker defined at the creation of the project as the reference elevation by checking the option “Use the elevation marker as zero elevation”. Check it.

Two points are removed from the best cosine curve computation in order to improve the coefficient of determination R².

You can then click on the graph in the dialog box to enlarge it over the 3D scene and be able to display information on each point when moving the mouse cursor on them.

Results from the differential settlement

Click OK to validate the results. A new folder called “Differential Settlements” is created in the tree. It contains the 50 points used for the computation.