May 19, 2020


Why is my force demand higher than what is reported in my force diagrams?


A question that we are asked from time to time in technical support is “why is my required force higher than what is reported in my force diagrams”. For instance, in the detail report below we can see that the maximum moment about the member’s weak axis is 28.9 k-ft. However, the required weak axis moment is reported as 31.8 k-ft.

Image 1

The reason there is a discrepancy between these two values is that the force diagram is solely reporting the moment about the weak axis whereas the required force is also including contribution from the torsional warping stresses. The required shear force shows a similar difference in that torsion is also included.

If you are using RISA-3D v18 and newer, you are able to access the new detailed reports which include the full limit state calculation that was used to determine the required forces. In this example, click on the “Applied Loading - Bending/Axial” or “Applied Loading - Shear” section for a breakdown of these calculations.

Image 2

After expanding the “Applied Loading - Bending/Axial” section it becomes clear that required flexural strength is derived from both the weak axis bending stress and the local warping bending stress.

For more information on how the expandable detailed reports can help you understand exactly how the program is deriving its calculations, check out the video below:


Tags: RISA-3D Reporting Detailed Reports

You may also be interested in

Nov 8, 2018 | Tips & Tricks
Mat Slab Overturning and Sliding Safety Factors

RISAFoundation v11.0 includes two new tabs in the Safety Factors resul...
Read More

Aug 21, 2019 | Tips & Tricks
RISA-3D v18 Sneak Peek Videos

The new release of RISA-3D is right around the corner! Check out our t...
Read More

Jul 12, 2019 | Tips & Tricks
Implementing Realistic Behavior for T/C Members in RISA-3D

Tension or Compression (T/C) Only members are commonly used in steel b...
Read More

Jun 20, 2019 | Tips & Tricks
Understanding Wall Panel Forces with Rigid Diaphragms

Rigid diaphragms represent a plane of very high rigidity and distribut...
Read More