March 11, 2025
ADAPT-Builder: Fixing Instability Warnings Due to Multiple Slabs
When working with ADAPT-Builder, in some models users may encounter an instability warning due to multiple slabs on a single level. This can be frustrating, but we're here to help! The root cause is typically related to insufficient boundary conditions allowing unintended translation or rotation....
November 13, 2019
Solving P-Delta Divergences in RISA-3D
In this video, you’ll learn how to investigate your RISA-3D model for P-Delta divergence errors. This type of error is common in general structural analysis software and has two major causes: a model that is unstable or a model that is too flexible. For this investigation, two separate steel frame...
October 19, 2016
Instabilities in RISA-3D with Flexible Diaphragms
In a model that contains both RISAFloor and RISA-3D data it is possible to define your diaphragms as either flexible or rigid for lateral design. You can do this from the Diaphragms spreadsheet in either program:
February 23, 2012
How Do I Resolve a P-Delta Instability?
Investigating P-Delta instabilities in RISA-3D (or RISA-2D) can be difficult. The first step is usually to solve the model without the P-Delta effect included to see if there are any obvious deflection problems that could cause issues with a P-Delta analysis. But, what can be done when this doesn’t...
June 13, 2011
How Do I Avoid Instability Warnings in a RISA-3D Model?
Have you ever received an instability warning when running a three dimensional RISA-3D model? This is because RISA-3D cannot build the stiffness matrix with the configuration you have modeled. In some cases, your model is truly unstable and in others it’s a matter of correctly modeling your...
May 10, 2011
Are You Receiving Instability Warnings for Your Truss Model in…
When running a truss model in RISA-3D or RISA-2D, it’s quite common to receive an instability warning, but these can be easily resolved by following a few simple rules.
March 9, 2011
How Do I Investigate My RISA-3D Model Using the Deflected Shape?
When your RISA-3D model is not behaving as you anticipated, one of the best tools you have is viewing the deflected shape. Displaying the deflection graphically will help you visualize how the model is behaving and will often times bring to light modeling errors.
January 18, 2011
How to Model Tension-Only Bracing in RISA-3D
Before reading this, be sure to check out the article linked below on X-Bracing. In RISA-3D, you can set a member to be tension-only by selecting it and selecting Tension Only or Euler Buckling from the Additional Properties section of the Member Properties.