
October 26, 2010
How to Use Spreadsheets More Effectively in RISA
RISA includes various advanced spreadsheet operations that make reviewing input and results easy.
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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RISA includes various advanced spreadsheet operations that make reviewing input and results easy.
To best understand how plates interact with each other you must first understand the concept of Physical Members. The important thing to keep in mind is that plates are not physical members. A plate is defined using either three or four joints, and it only connects to other plates at those joints....
When you have a deep column, it is necessary to model the beam so that it connects to the face of the column. This results in an eccentricity at the joint. RISA-3D offers two ways to model this eccentricity.
The customizable toolbar is a new feature in RISAFloor. It’s really useful and you may have overlooked it. You’ll find all of your familiar buttons as well some new buttons which make reviewing your model and results easier.
There are four different values for Unbraced lengths in RISA-3D, RISA-2D and RISAFloor. Two are for axial calculations and two are for bending calculations.
Members (beams, columns, braces, etc.) are defined in RISA by an I-Node and a J-Node. While you and I see a beam occupying physical space between two columns, most programs see a line between Point I and Point J. This is known as a non-physical member. See the image below:
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.
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