Moment of Inertia

[Rodrigo Pena]

Hello all, hope you are doing great.


I am building an spreadsheet to calculate the reactions on 3D bolt group and I would like to confirm an information.

I calculated the moment of inertia about the centroid of my bolts in all 3 planes, my question is:

Can I add Ixx from xy plane and Ixx from xz plane ? I have to come up with only 1 Ixx to calculate the constants.

Thanks !

 

[rb1957]

not really sure what calc you're doing ... can you show the geometry ?

I'm not sure how you get two inertia terms for all three axes ? I'd've thought that there be only one term ... unless the plane of the fasteners is generally inclined (but then you'd transform loads into this plane ... won't you ?).

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

 

[Rodrigo Pena]

The geometry is a circle, the diameter of the bolt is 0.18 in^2.

my spreadsheet is enclosed. go to 3D bolt group and formulas and calcs tab

 

[rb1957]

your attachment is a screen shot.

If you have a bunch of bolts on a PCD, then you have Ixx = sum(A*y^2) = Iyy. You could calc Izz, but I'm not sure why you would (but in any case = 2*Ixx).

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

 

[Rodrigo Pena]

Sorry,

Link

I don't know if you can access the file by clicking in the link above.

 

[rb1957]

yes, now you've linked your s/sht.

I don't know I'd consider the Z (= 4) term and calc Ixz and Iyz.

You seem to be doing a lot with this. I don't think I've ever seen people include the local I of the bolt (and just use Ay^2).

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

 

[Rodrigo Pena]

I see... I got some results that matches with other spreadsheets.

Thanks !