FAQ 000087 EN

1 December 2017

Robert Vogl Calculation SHAPE-THIN RF-STEEL STEEL

I have idealized a taper by using a start and end cross-section (calculated in SHAPE-THIN) and calculated a frame. During the stress calculation in STEEL, the error message 'Tapered member contains incompatible cross-sections' appears. What is the error?

Answer

This message appears if both cross-sections of the taper have a different number of stress points.

The stresses in STEEL are determined with the second moments of area and the distances to the stress points. Now, if the taper's start and end cross-section have different numbers and locations of stress points, the program cannot interpolate the intermediate values. In the rendering mode, no taper is often displayed but only the two cross-sections at the start and end. You can see a 'break' in the middle of the member.

You can look at the stress points of a cross-section in its details. With a click on the button [Details of Stress Points] you can open a table showing the exact values for the stress points (number, location, and so on).

To solve the problem, you have to create the same number of stress points. You can do it, for example, by creating a cross-section at the end of the taper as a copy of the start cross-section and adjusting the height. However, the original form must be preserved. Therefore, it might be necessary to also model a very small strengthening.

You can also create the tapered cross-sections with the sections of the RSTAB library: For this purpose, there are the 'Strengthened I-Section with Lower T-Section' among the welded cross-sections.

Keywords

stress point taper incompatible cross-sections stress

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