# Centre of Mass

Hi all,

I am looking to calculate the centre of mass of a structure. I notice that this is an output of the eigenvalue analysis, however these results are not consistent with the linear analysis. The output of the centre of gravity should lead to up uplift at the forward support but this doesn’t happen.
I have two questions?

• What exactly does the output of the centre of mass mean?
• Does it consider all the loads assumed as masses or only the self-weight?
• Is there an easy solution (apart from static analysis) to output the centre of gravity of all the permanent loads on the structure?

Thank you!
Ines

Hello Ines

As far as I know, the center of mass calculated by the eigenvalue analysis only takes into account the applied masses (dead loads). So if you want to include all loads, you can define a fixed node (preferably at the origin), couple all support nodes to that single node, and calculate the center of mass by hand (Mx/Fz=ey and My/Fz=ex).

Here’s an old post on calculating the center of mass:

Best regards
Frederik Höller