Wall Panel Boundary Conditions: Frequently Asked Questions

Wall panels in RISA-3D let engineers design and analyze multiple structural systems in a single model. Correctly applying boundary conditions at wall panels is critical to accurately represent the structure’s behavior. This FAQ answers common questions about how to set up wall panel boundary conditions and how RISA-3D handles them in the analysis.

How do I apply continuous boundary conditions along a wall panel edge?

1. Open the Wall Panel Editor

• Double click on the wall panel in the 3D view to open editor

• Use this editor to customize the wall panel including adding openings, changing materials, and assigning boundary conditions

2. Select Boundary Conditions

• Click the Boundary Conditions button in the upper left corner under the Walls tab

• Use one of the preset options as a starting point: Free, Fixed, Pinned, or Roller

• For custom restraints, set each degree of freedom (DOF) to Reaction or Free

3. Assign Boundary Condition at an edge

• Click on a snap point along the edge of the wall where you'd like to apply the boundary condition

• The boundary condition will be applied to the entire length of the edge selected
• Once assigned, the wall boundary condition will show in orange in the model view

How does RISA-3D model continuous boundary conditions? 

RISA-3D utilizes an internal mesh to analyze wall panels. The boundary condition is applied at the internal nodes created by this analysis mesh.  This approach approximates a continuous condition while optimizing the run time of the model.

A couple of key points: 

• The wall mesh defaults to an approximate section size of 24 inches

• The mesh size can be changed under the Solutions tab in the Model Settings window 
  

• After solving, the user can display the wall analysis mesh using the Results View Settings under the View tab 
  

It is good habit to briefly review the mesh to confirm it aligns with your expectations prior to finalizing the results. 

What's the difference between nodal boundary conditions and wall boundary conditions?

Both nodal and wall boundary conditions are external restraints that remove load from the model and generate reactions. The primary difference is how they are applied.

Nodal boundary conditions:

• Applied to a specific node only

• Shown in green in the model

• Added directly from the Draw Elements section under the Home tab 

Wall boundary conditions: 

• Applied along the length of the wall

• Shown in orange in the model
• Added through the Wall Panel Editor as detailed above

Should I use nodal or wall boundary conditions to restrain wall elements in my model? 

For most applications, the wall boundary conditions will provide a realistic restraint for the as-built condition by approximating a continuous support.  However, both boundary conditions can be used to restrain a wall element so choosing the correct boundary condition will depend on the assumed behavior of the wall. 

To better understand the different behavior based on the selected boundary conditions, see the side by side example below showing both the calculated reactions and the deflected shape of the wall panel.  Here you can compare 3 different boundary conditions:

• continuously pinned connection using a wall boundary condition

• pinned connection using node boundary conditions spaced to mimic the wall panel mesh size

• pinned connection using node boundary conditions only at end supports  

How can I view my reactions at the wall panels? 

To view the reactions at your wall panels: 

• Use the Node Reactions spreadsheet for the total reaction at the base of the wall

• Use the Reactions option in the Quick View toolbar to graphically show the reaction distribution at the nodes

For a deeper dive into interpreting these results, check out the article below which provides more details.