Application	PLAXIS 2D
Issue status	Solved
First Affected Version	PLAXIS 2D Anniversary Edition
Found in Version	PLAXIS 2D Anniversary Edition PLAXIS 2D 2015-2019 PLAXIS CONNECT Edition V20-V22 PLAXIS 2023.1
Fixed and Released in Version	PLAXIS 2D 2023.2
Issue #	1092643
Date created	20 March 2023
Date modified	01 August 2023

Problem description

PLAXIS 2D allows modelling using plane strain or axisymmetric conditions. Point loads can be used to simulate a force applied on the soil and/or structures, and in both model definitions, the input values for these point loads are defined as force per length unit in the out-of-plane direction, e.g. in kN/m.

However, when using dynamic point loads in axisymmetric models, the applied point force for just the dynamic component is not considering the radius, e.g., the distance from the axis of symmetry (at X=0).

This happens only for the dynamic component of a point load in axisymmetric models, for other load components, this works correctly.

This can be confirmed, for example, by checking the structural forces on plates or other structural elements when only using a dynamic point load (no static component active) as seen below.

Figure 1. Selection explorer of the point load – dynamic component is active

The resulting applied force in the results is expected to be equal to the dynamic load value as defined in the Input program. Instead, because of not including the radius of this point load location, the actual applied load value is not equal to the expected Input value.

Workaround

This issue is now resolved in PLAXIS 2D 2023.2.

Versions PLAXIS 2D 2023.1 or earlier

For older PLAXIS versions, the only way to retrieve accurate results is to compensate for this in the Input value for the point load by applying a dynamic point load value that considers the radius, i.e., distance from the axis of symmetry.

To do so, in PLAXIS Input, the provided dynamic point value would be equal to the resulting dynamic force multiplied by the radius considered in the axisymmetric model:

F_{y, ref} = F_y,result * R

• F_{y, ref} : Input point load value
• F_y,result : Output point load value (result)
• R: radius, distance from XMin axis of symmetry

Example for testing

To verify the workaround provided, a simple geometry of a single vertical plate is considered, in which three scenarios are tested:

1. Case A: Static - an analysis is performed by means of a Dynamics calculation type in which only the static component of the point load is active.
2. Case B: Dynamic - an analysis performed by means of a Dynamics calculation type in which only the dynamic component of the point load is active.
3. Case C: Static + Dynamic - an analysis is performed by means of a Dynamics calculation type in which both the static and the dynamic components of the point load are active.

In all cases, the value provided for the point load in Input is shown as well as the results in the Output program.

Note that specifically for Case B and Case C, the value of the dynamic component of the point load is computed based on the aforementioned workaround which considers that the final point force to be applied is F_{y, result} = 11 kN/m.

The Input value is therefore, according to the workaround suggested, configured as:

• F_y,ref = 5.5 kN/m (F_{y, ref} = F_y,result * R)
  • R = 0.5m (location of the plate)
    

Figure 2. Case A: Static load is active – no dynamic load is considered

Figure 3. Case B: Dynamic load is active – no static load is considered

Figure 4. Case C: Static and Dynamic loads are active

Figure 5. Axial forces on the plate due to static load (Case A), dynamic load (Case B) and both static and dynamic load (Case C) – resulting force should be 11kN/m per point load component activated

This issue will be fixed in our next release of the application (PLAXIS 2D 2023.2).