March 17, 2010

Do You Ever Get the “LOCKED” Message on a Simple Beam Model?

By: RISA

Do you get an instabilities warning when you’re trying to do a simple 2D model in RISA-3D?

Below is the easiest way to test and fix the instability:

Open the Node Reactions spreadsheet, and see which joint is unstable.

In the Boundary Conditions spreadsheet, apply a Reaction to the joint in the degree of freedom that was LOCKED.

Re-run the model and examine the Node Reactions.

If the reaction that is restraining the instability is showing a ZERO force or moment, then the instability is inconsequential to the results. Also, if the reaction that is restraining the instability is showing a non-zero force or moment, then you have a problem with the model that must be corrected for you to get valid results.

Tags: RISA-3D, New, Instability

May 10, 2011 | RISA-3D, New, Instability

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. Rule #1: Every joint in your model needs to have at least one member with a fixed end release. In trusses, it’s typical to have all members with pinned end releases so be sure to change the end releases to comply with this rule. Rule #2: Brace the truss so it doesn’t “flop” out of plane. You can do this by creating an additional boundary condition to brace all of the joints for any out of plane motion. Assuming the truss is in the XY plane, below is the boundary condition you can add:…

June 19, 2014 | RISA-3D, Loads, New

How to Use Moving Loads

RISA-3D and RISA-2D will allow you to add a moving load pattern to your model and include it in your envelope solution. 1. Adding a New Moving Load Pattern To learn about adding new moving load patterns to your Moving Load Patterns library, please see the How Can I Add a New Pattern to the Moving Load Database blog. 2. Defining the Moving Load Path Once you have added your moving load pattern, you can apply it to your model in the Moving Loads spreadsheet (Spreadsheet > Loads > Moving Loads). In this spreadsheet, you will define the following: Tag: Label of the moving load (this cannot be changed). Pattern: Select the moving load pattern from the dropdown menu. This menu reads in all the patterns that are listed in your moving load library (Advanced > Moving Loads). Increment: Specify the distance at which the load will be stepped through the path. Both Ways: If you want the load pattern to reverse once it has reached the final node along the path, check this box. Node Entries: These define the path of the moving load. Note: You may skip intermediate points along a straight line when specifying the path. 3…

March 9, 2011 | RISA-3D, RISA-2D, New, Instability

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. Turn on the deflected shape by clicking on the Result View Settings button on the Home tab. Or by clicking on the Deflection button found on the View Toolbar. After the deflected shape is enabled, it is possible to increase the magnification factor of the deflection so that individual locations can be evaluated in more detail. The deflected shapes pictured below illustrate two simple braced frames. These two images are a perfect example of how you can get seemingly good results including reactions, code checks and even Joint Deflections for both frames. However, the right frame above shows that the beam is not connected to the column or brace. You need to display the deflected shape in order to catch this modeling error…