July 17, 2025

How RISA-3D Handles Wall Surface Loads at Openings

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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