difference in results between version 2018 and 2025 / participating mass / modal analysis

[danielroure2267]

Hello,
I would like to know if you have noticed any differences in the calculation of participating masses during modal analyses between versions 2018 and 2025 of Robot Structural Analysis.
I performed the same calculation on an identical file, once with RSA 2018 and once with RSA 2025. However, the results for the participating masses differ between the two versions. Here's what I checked:
- Mass conversions are identical in both cases.
- metrics are identical
- The modal analysis parameters are also identical.
- The sum of masses is greater than the sum of reactions in version 2025, which seems coherent since in my load case, only negative Z actions are converted to mass (positive Z actions are not).
Despite these checks, I can't identify the cause of the discrepancy. Do you have any clues or explanations?

[danielroure2267 · Accepted solution]

in the end, the discrepancy is due to the fact that in 2018, the coefficient applied to the deadweight line was not taken into account, unlike RSA 2025, which was a bug in 2018.