March 18, 2016

How Do I Find A Failing Member in the Model?

You may find that when looking at the Code Check spreadsheet that a given member is failing in design. Here is an example where a steel brace is failing in bending.

However, for a large model it may be difficult to know where this specific member is located. The quickest way to graphically identify the failing member is to highlight the row of the member in question, right-click and choose Select Marked Lines in Current View.

Within the graphical view, the member in question will be the only one highlighted and you can begin to investigate why the member is failing.

Tags: RISA-3D, Results, New, Graphics

August 31, 2016 | RISA-3D, New, Steel

Why Do My Wide Flange Members Fail in the AISC 14th Edition Code?

In RISA-3D’s addition of the AISC 14th Edition code we added Section E4 checks to wide flange members. Section E4 is Torsional and Flexural-Torsional Buckling of Members Without Slender Elements and is for compression capacity. Specific to wide flanges is the Fe equation E4-4. In that equation is a reference to L, which is referring to the torsional unbraced length. In RISA-3D this is defined in the Members spreadsheet – Hot Rolled tab and defaults to the full length of member, similar to other unbraced lengths. This can cause a reduced compression capacity compared to what is found in Section E3. If you notice a wide flange member that passed in the AISC 13th Edition and is now failing in the AISC 14th Edition, this may be the cause. A quick way to confirm this is to update the L-torque value to 0 and see if you now getting a passing check…

May 19, 2020 | RISA-3D, New, Reporting, Detailed Reports

Why is my force demand higher than what is reported in my force…

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. 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. 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…

November 20, 2013 | RISA-3D, New, Torsion

Why Is My Beam Failing in Shear?

When solving a RISA-3D model you may find you have a Shear UC (unity check) much higher than expected from bending shear alone. If you open the detail report and compare the shear demand to the shear capacity you may see that the demand/capacity is less than the Max Shear Check reported. What is likely occurring is that the member has torsion in it. In RISA-3D both the bending and shear demands are affected by torsion, though it is shear that usually causes the most problems. If you look at the detail report and in the Member Torsion spreadsheet results you can see this torsion. Warping Member (Wide Flange, Channel, etc): Non-Warping Member (Tube, Pipe, etc): Generally speaking wide flanges and channels work very poorly in torsion, while tube sections are much more efficient. Eliminating torsion or using a more efficient section are common ways to eliminate this problem. Note that this torsion problem can happen for all material types…