Strong Moment of Inertia of Arc

[kranic24]

I am in search of basic formulas for determining the strong moment of inertia of an arc. I know the equatin for weak and know the integral method to determine the strong. I need a quick formula. For example, an arc of radius 14inches and thickness of 1/8" (cross section of half a pipe). The answer should be about 530in^4.

Thanks in advance.

 

[rb1957]

sorry, but if you Know how to calc the weak axiz MoI, then you Should know how to calc the strong axis MoI.

you should notice that the weak axis is aligned so the the material is close to the axis, so the strong axis is aligned ???
also the strong axis is at 90 deg to the weak axis (for the reason noted above).

the accurate value is a little difficult to calc ... you need to integrate the element dA defined as a length Rdtheta and a width t/sin(theta) for theta between + and - 45deg ... clear as mud ?



Quando Omni Flunkus Moritati

 

[kranic24]

Thanks rb for reply. I was in search of formulas without integration. I have since located formulas that return what I need. Anyone in need of formulas like this should check out "Handbook of Equations for Mass and Area Properties of Various Geometric Shapes" compiled by Jack Myers - 1962.

The answer to my question was (pi/8)*((Outer Radius)^4-(InnerRadius)^4)).

 

[IDS]

You might find my section properties spreadsheet useful (copy attached):

More on section properties


Doug Jenkins
Interactive Design Services

http://newtonexcelbach.wordpress.com/