February 5, 2014

How to model a Geodesic Dome in RISA-3D?

In modeling what would be a rather difficult geometric structure, by using the Templates database in RISA-3D, a geodesic dome can be constructed rather quickly and easily.

Select the "Geodesic Dome" from the "Templates" drop-down found on the Home tab.

The following dialog box will be displayed and you can enter in the necessary information for the geodesic dome generation:

Platonic Solid Shape: Designates the overall shape, number and orientation of the geodesic dome
Triangle Subdivision: Designates the number of triangle submesh per side of the triangular plate
Polar Origin: Sets the origin (insertion) point of the dome
Members: Allows for the creation of strut members using a material and pre-defined section set
Plates: Allows for the generation of plates using a material and thickness
Dome Height/Radius: Sets the geometry of the dome

Once the properties of the dome have been defined, click OK to generate the dome.

Tags: RISA-3D, New, Geodesic Dome

January 18, 2011 | RISA-3D, New, Instability

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. Link: Tips & Tricks: X-Bracing In the example below, if the braces are set to Tension-Only, the model will register as unstable: Under gravity loading the elastic shortening of the columns will cause some elastic shortening of the braces. This means that each brace is slightly compressed (with about 50 lbs of axial force). When the braces are set to Tension Only they are not allowed to take any compression at all, so they are both ignored during the solution, resulting in an unstable frame. By setting the braces to be Euler Buckling instead of Tension Only, the program will allow these braces to take compression only up to their Euler Buckling limit, which is enough to compensate for the elastic shortening. If any significant compression enters the brace it will still be ignored during solution…

August 16, 2018 | RISA-3D, New, Cables

Modeling Cables in RISA-3D

One of the support questions we get most often is, “How can I model a cable element in RISA-3D?” Cables that are straight and experience only axial loading can be easily modeled. When modeling structures with cables (such as guyed structures) the cables can be modeled as tension only and doing so will ensure that the member will not take any compression. Click the link below to our RISA-3D Help File. Search 'Tension/Compression-Only Members'. RISA-3D Help File In addition to setting the member as tension only, it is necessary to utilize a weightless material so that the transverse cable member deflections are not reported. To do this, you can create a new material and set the density to zero. Note: If the cable weight is removed, it should still be applied elsewhere on the structure as a point load. If you do not do this then the cable deflections (other than the axial deflection) will be reported as very large since it is the cable action that keeps a guyed cable straight. Lastly, if the design requires a cable prestress, thermal loads can be used to create the pre-tension of the cable. See Prestressing with Thermal Loads to learn how…

August 27, 2014 | RISA-3D, New, Analysis

What is a Rigid Link in RISA-3D?

A rigid link is a member element in RISA-3D that can be used for many advanced modeling procedures. It is so useful that it is included as one of the default member Section Sets, as you’ll see below. On the General tab of the Section Sets spreadsheet there is a default “RIGID” Section Set that uses the “RIGID” material. You can see the cross-sectional properties make the section very rigid. You can also open the General tab of the Materials spreadsheet to see the material properties assigned to the “RIGID” material. It has very stiff material properties with zero density so that it does not create any erroneous additional self-weight. As you can see from the properties above, a dummy member is a very stiff member which can be used to help transfer forces from one point to another. This can be useful for a number of advanced modeling techniques in RISA-3D, such as offsetting elements or modeling composite behavior. A great example of how to use Rigid Links is Offset Connections. Another use for these rigid link members is in RISA-3D rigid diaphragms. Click here for information on Rigid Diaphragms…