Calculating Second Moment of Aria for Hollow Square Beams

[a5hl3yi]

Question:

How do you work out the second moment of aria for a hollow square beam?

Attempt:

I have looked over my notes and it says how to get the second moment of aria for all beams but a hollow square one. It has I beam, Circulare beams, Rectangular...

How do you go about working it out for a hollow square beam?

 

[minger]

Basically you just take the area moment of a solid square 100mm a side and subtract off the inside.

 

[a5hl3yi]

thanx.

So does that mean I would work out (100mm x 100mm) - (70mm x 70mm) and us that as the aria in the formula or work out the Moment of aria for the 100mm x 100mm and take off the moment of aria for a 70mmx70mm square?