Why do I get different design results for a load combination (CO) and a result combination (RC) in STEEL EC3 despite the same internal forces?

Answer

The difference between a design with RC and CO lies mainly in the moment distribution applied for the calculation of the elastic critical moment Mcr. For a load combination (CO), it is possible to apply explicitly the moment distribution for the existing load position. However, the result combination (RC) can only analyze the enveloping of the moment distributions. Then, the more unfavorable distribution (Max or Min) is applied. As a consequence, unfavorable values result for the critical load factor.

Summary:
The internal forces applied for the design can be the same in LC and RC, but the moment distribution in the result combination is applied more unfavorably to determine the critical branch value. Thus, the RC provides a higher utilization for the design with STEEL EC3.

Keywords

Result combination Load combination Design Lateral-torsional buckling

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