Structural results in tables and curve plots

Description

With PLAXIS Output, you can review and inspect all calculation results, including soil/rock and structural elements. With regards to structural element results, apart from the plots and cross-section curves (2D only), it is common to check both the tabulated results and create various curve plots using any selected post-calculation curve nodes.

More information on selecting nodes for curves can be found in the article Selecting points for curves.

One may notice that the results shown in a table may differ when compared to the values displayed in the curve plot. Typically this is influenced by the density of the generated finite element in the area of the structures.

In this article, we will explain the reason why there is a difference, and how you can ensure that you have reliable results.

Selecting a structure to view results

The first PLAXIS Output plot after loading a phase calculation result is the Deformed mesh (Figure 1). To view the results for a specific structure, you can use different methods.

Figure 1. Deformed mesh for both soil/rock and structures 

Depending on the deformations and the scale factor, the structures may not be fully visible. Therefore, hiding some of the existing objects can help focus our view on the area of interest (Figure 2). In some cases, you can also switch to the Connectivity plot (Ctrl + 0), found under the Mesh menu. 

Figure 2. Toggle objects visibility on the explorer 

To select a structure, you can follow one of the suggested workflows below:

1. With your left-mouse button (LMB), double-click on the structure
2. Use the Select structures icon from the side toolbar, press Enter or click with your right mouse button, and select the Structures option.
3. Use the Window selection of structures icon from the side toolbar, select the structure (if multiple exist) and click on the View option.

Figure 3. Selection of structures in PLAXIS Output – option 2 

When you select a specific structure, it is possible to select the whole object or specific parts of it. The various parts are the structural elements created during the meshing process. In most cases, either the whole object or multiple structural parts are selected. 

Following the selection, you will change to a Structure’s plot, recognizable by the different icon at the bottom left of your plot, as shown in Figure 4. 

Figure 4 . Structure plot for a beam, showing the nodes and node numbers

Reviewing results for structures in a table

Following the example above, a specific beam was selected, Beam_2_1. You can click on the table icon at the top toolbar to access the results in tabular form.

Figure 5. Table of results for selected beam with result smoothing

You will notice that the results for this beam are ordered in a specific way, by default by structural element, by node number and by local number. You can also identify that the connected beam elements share a node number at their connection, e.g., Node 783 in Figure 5.

In this table, the results for both structural elements and the results for forces are identical for the case of Beam_2_1, Element 7-53, and Element 7-52. The reason is that by default, the Use result smoothing option is selected, which assists in reducing the numerical noise resulting from the extrapolation of the results obtained in stress points (e.g., stress, force) to nodes. For more information on the Use result smoothing option, check our Reference manual.

However, when deactivating the Use result smoothing option, you can see that the results for the same nodes are now different as the Output program no longer considers a smooth transition from one structural element to another, i.e., Beam_2_1 Element 7-53 to Beam_2_1 Element 7-52.

Figure 6. Table of results for a selected beam without result smoothing

Reviewing results for structures in a curve plot

Following the same example, a curve plot will be created to capture the full history of a specific node of the beam object, Beam_2_1.

PLAXIS Output offers multiple ways of selecting a node for curves. For a structural element, this can be done by:

1. Searching by coordinates or node number (id) and selecting the relevant points
2. Selecting a curve point when viewing a Structure plot, based on the displayed result

Figure 7. Search for a curve point by id – exact element shown when hovering with the mouse pointer

Figure 8. Select a curve point to create a chart using the right-mouse button option

In all cases, the selected post-calc node will be added to the curve points list and you can now create a curve plot.

For the case of structural forces by plotting both selected nodes for each structural element, as seen below in Figure 9, you will notice the small difference in results, which corresponds to the results shown in the table when the Use result smoothing option was deselected (Figure 6).

Figure 9. Results for selected nodes per structural element

Summary

The topic explained in this article can be summarized in the following points:

• Structural objects comprise structural elements, created during the meshing process.
• Selecting structures can be done per object or per element(s), and the results on the table correspond to the displayed parts.
• The “Use result smoothing” is an option to reduce the numerical noise from the extrapolation process but can be deactivated if the results are to be viewed disregarding the neighbour elements. To achieve more accurate extrapolation refining the mesh may be required.
• Curve points can be selected to create curve plots based on structural elements, which will only show the actual nodal value for the selected curve point.