Question
What is the Section for Resultant Force, and how does Midas calculate this resultant force?
Answer
As the name suggests, it is a virtual beam, not a real beam. This virtual beam does not have material or section properties. Essentially, the forces are calculated at each location of the elements assigned to the virtual beam, and the resultant force is transferred to the location of the virtual beam.
The concept of the virtual beam involves the i-end and j-end of virtual sections. The virtual beam will not be visible to the engineer but needs to be defined to calculate the resultant force diagram. The local axis of the virtual section can be viewed by checking the relevant option in the Display > Property tab.
At this location, the resultant forces are calculated.
To further clarify, let's take a simple example of a cantilever beam of 10m length with a point load of 60 kN applied at the end.
As we can see in the above image, the results for beam elements and virtual beams are similar.
Note: If the virtual section does not lie on the nodal position, the Resultant Force Diagram can be displayed in an uneven shape as shown below. It is because the program calculates resultant force using the nodal forces. To prevent an uneven diagram, it is recommended to generate a virtual section line on the nodal position.
If it doesn't align automatically. We can manually update it's position by changing the coordinate as shown in the image below.
In the below image, we have changed the virtual beam position to the center left position.
Since the virtual beam position is changed. additional torsion moment is also generated in the virtual beam. So, it is important to check the position of the virtual beam by checking its local axis.