Calculating second moment of area of L section

[wicz]

Hi there,

I currently trying to calculate the second moment of area of an L shaped cross section.
The reason for this is I have carried out a buckling experiment on a strut of this cross section and want to calculate some theoretical results to compare to my experimental results.
I need the second moment of area so I can use Euler's equation and calculate the axial load on the strut.

I have attached my workings for the second moment of area, but in all honesty I do not think my method is correct. It would be very helpful if someone wouldn't mind looking over my calculations and point out where I have gone wrong. It would be very much appreciated!

Thanks

Max

 

[wicz]

Have just realized it is not clear on my diagram that the dimensions of the cross section are in mm.

 

[wicz]

At the risk of being caught talking to myself...

I think I may have figured this out, I've attached a print screen of an excel spreadsheet I used to do the calculations.
Obviously because its excel you can't see my workings, but maybe you can tell if my values look correct?

 

[OldEngr63]

It appears that you have set up to calculate second moments with respect to centroidal axes parallel to the axes (this is an obvious thing to do). Your strut will not buckle on these axes, however. It will buckle on the weak axis, which is the axis of minimum area moment of inertia. You need to take the values you obtain and go into a Mohr's circle calculation to obtain the max and min values of the MOI. This will give you the value you need to compare to your experimental work.

 

[wicz]

Thanks for your help, all sorted now :)