How to determine the total second moment of area of a section containing beam elements

[daanamsterdam]

As a student I'm working in a FEMAP model of an heavy lift ship. I'm looking for the second moment of area of the total vessel so I can create a representative equivalent model as well as being able to compare the results with hand calculations. The cross sections contains beam elements for these elements I can only obtain the second moment of area but in a local coordinate system. How can I find the neutral axis and the second moment of area of the vessel as a whole and of cross sections of the vessel.

Thanks,

Daan

 

[rb1957]

do you know about the parallel axis theorem ?

total I = sum(Io+Ay^2) for all component pieces of the section, where
Io = the MoI of the piece about it's CG
A = the piece's area
y = the distance from the piece CG to the section CG

another day in paradise, or is paradise one day closer ?

 

[daanamsterdam]

rb1957,
Thanks for your reply!

I know about the parallel axis theorem. The problem is that a cross section of the model contains a lot of area's with complex shapes. I was wondering if there is a way to let FEMAP calculate the total second moment of area for a model.
I would assume the second moments of area are also calculated in the global coordinate system(CoG), as the simulator requires this to calculate the displacements etc. Can these numbers be displayed (for individual beams, a section as a whole, or the entire vessel)? Some of the beams are rotated. I therefore assume FEMAP performs a local-to-global coordinate transformation.

Thanks again,

Daan

 

[rb1957]

it would be easier to have AutoCAD (or similar) to calculate the overall section I.

I wasn't thinking of doing this in FeMap, but rather Excel. If you have the three I's for a component about an arbitrary axis, then it's simple to rotate to another axis.

another day in paradise, or is paradise one day closer ?