
January 6, 2011
How to Model X-Bracing in RISA-3D
There are several tips to modeling X-Bracing within RISA-3D that can help the model solve faster and give you better results.
When designing shear walls in RISA-3D, it’s common to add surface loads—whether to simulate lateral wind or seismic pressures, or even out-of-plane loads. But what happens when those loads intersect with openings in your wall panels? Let’s walk through exactly how RISA-3D handles this scenario behind the scenes, including how the program preserves total force and moment equilibrium—even when wall geometry gets complex. ⚙️ How It Works: Surface Load Redistribution at Openings When a surface load is applied to a wall panel that contains openings, RISA-3D uses a special algorithm to redistribute the portion of the load that would otherwise fall inside the opening. Rather than ignore that load entirely, the program converts the "lost" surface area into equivalent nodal forces along the edges of the opening. These loads are known as transient nodal loads. Here’s the step-by-step breakdown: Determine Centroid of the Loaded Region RISA calculates the centroid of the area made up of both the surface load region and the opening. Split the Load Across the Opening The surface load over the opening is divided into two halves, based on the centroid location. Distribute Equivalent Forces Along Opening Edges These two portions of the load are then “smeared”…
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There are several tips to modeling X-Bracing within RISA-3D that can help the model solve faster and give you better results.
When it comes to trusses in RISA-3D, boundary condition definitions (pin vs. roller) can make a huge difference. Let’s take an example of a typical roof truss. Note that a pin-pin boundary condition has been applied to the ends.
If you have ever tried to solve a two-dimensional model in RISA-3D, you have ultimately run into instabilities in your model because your model has no out of plane restraint.
Do you get an instabilities warning when you’re trying to do a simple 2D model in RISA-3D?
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