August 17, 2016

How Does RISA-3D Account for Torsional Warping?

Twisting of a member or frame induces torsional forces and stresses. This is included in the RISA-3D analysis as long as you have the Torsional Warping checkbox selected on the Solution tab of (Global) Model Settings.

The primary reference used in the development of RISA-3D’s torsional calculations was the AISC Design Guide #9, Torsional Analysis of Structural Steel Members.

It is important to remember that RISA-3D models warping members using CASE 2 only. As shown in the Torsion reference, CASE 2 represents the torsionally fixed and warping fixed end conditions for the member. Thus, a member would be then subjected to an equal and opposite point torque at the end of the member.

Note: RISA’s calculation of torsion stresses is good for capturing the torsion due to racking of the structure, not point or line torques on an individual member. That type of check is not supported.

Stress Results

RISA-3D calculates and lists the torsional stresses for the members of the structure, including the warping stresses. These are reported in the Member Torsion spreadsheet.

For warping shapes (I’s and C’s), three separate stresses are calculated: pure torsion shear, warping shear and warping normal (bending) stresses.

Code Check Results

These torsional stresses are included when the AISC code check (ASD or LRFD) is calculated for the member. The shear stresses (pure torsion and warping) are included in the shear check and the warping normal stresses are added to the weak axis bending stresses for calculation of the combined code check. For more information about how RISA-3D includes the shear stresses in the steel beam design, visit the article linked below:

When including shear stresses from torsion in the shear code check, the program uses the worst case of the torsional shear stresses (top and bottom flanges or web) and combines that with the actual shear stresses due to pure flexure. This is intentionally conservative in cases where the worst case torsional shear occurs in the flange, but the worst case flexural shear occurs in the web.

Tags: RISA-3D, New, Warping, Torsion

October 30, 2020 | RISA-3D, RISAFoundation, New, Basic Load Case, v19, Loading, v13

Expanded Load Categories in RISA-3D and RISAFoundation

New to RISA-3D v19 and RISAFoundation v13 is the ability to apply up to 100 "Other Load" Categories. Previously users only had the ability to add up to 10 "Other Load" Categories. The expansion of "Other Load" Categories gives the user more flexibility to be able to apply and organize the loading in the model to fit their needs. To apply "Other Load" Categories in RISA-3D, simply select the "Other Load" Category from the drop down menu when drawing loads. To include the "Other Load" Categories in the Load Combinations in RISA-3D, you may either enter OL1-OL100 in the BLC field or you can select the ellipses to prompt the Set BLC Entry and select the "Other Load" Category from the drop down menu. To apply "Other Load" Categories in RISAFoundation, choose the "Other Loads" from the dropdown on the Distributed Loads Spreadsheet (or in the left Properties Toolbar) and choose a value between 1 and 100. To include these "Other Loads" in Load Combinations, you may either enter OL1-OL100 in the BLC field or you can select the red arrow to prompt the Set Category Entry and choose the "Other Loads" radio button and input a value between 1…

September 27, 2018 | RISA-3D, New, Analysis

Using Analysis Offsets in RISA-3D

Have you ever wondered what the Analysis Offset feature does? Let’s take a look at how this feature can be used to model members at top of steel. The analysis offset feature allows a member to be offset from its centerline for analysis. When it is enabled the member is actually shifted to the offset location for analysis. In order to provide connectivity the program places hidden rigid links to connect the member to the nodes that define the member’s I/J Joints. Joints which fall along a physical member are also automatically connected to the member’s actual analysis location via hidden rigid links. You can access the analysis offset by clicking on the member or through the Advanced tab of the Members spreadsheet. When the analysis offset dialogue is opened, the software will present the user with options for offsetting the member from its original centerline. The most common option for analysis offset is Local -y axis, which equates to setting the analysis line at top of member. Using this setting for the beam in a simple frame system allows for a more realistic representation of the structure (which can be seen graphically when the rendered view is enabled). It…

December 14, 2011 | RISA-3D, New, RISASection

How to Import a RISASection Shape into RISA-3D

RISASection 2.0 includes the ability to assign your section as one of the predefined hot rolled steel Shape Types (Wide Flange, Channel, Tube, etc.). This means that when the shape is imported into RISA-3D, you will now be able to get design results and code checks for the member. First, make sure that you assign the appropriate shape type in the Section Information dialog in RISASection. Save the RISASection file. Where does your RISASection file need to be saved? Open RISA-3D. Launch the RISA-3D application on your computer. Access Application Settings. Go to the menu bar and click on File, then select Application Settings. Locate the File Locations Tab. In the Application Settings window, navigate to the File Locations tab. Find the RISASection Files Line. Look for the line labeled RISASection Files. This is the location where RISA-3D will search for any RISASection files to import. Move or Adjust the File Location. Option 1: Move your RISASection files to this location so that RISA-3D can find them. Option 2: Change the File Location to where your RISASection files are currently saved. Save and Close. Once you've made the necessary adjustments, click OK to save your settings and close the window…