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Second Moment of Area calculation?
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[QUOTE="SteamKing, post: 4938751, member: 301881"] I think the trouble you are having with deriving the second moment of area for the weld lines is that the formula in the table attached to the OP is in a weird form, and is certainly not in the simplest form it could be. If you take what is shown and use the definitions of A and y-bar, substituting them into that formula for I, you will see that after some algebraic manipulation, you wind up essentially with the parallel axis theorem applied to this weld configuration, namely I[SUB]NA[/SUB] = I[SUB]y[/SUB] - A * (y-bar)[SUP]2[/SUP], where I[SUB]NA[/SUB] - moment of inertia about the centroidal axis I[SUB]y[/SUB] - moment of inertia about the top of the section A - weld area y-bar - centroid location Remember, the moment of inertia of the horizontal weld line which is b long is essentially zero, and the MOI of a rectangle about its base is d[SUP]3[/SUP]/3 (the MOI of a rectangle about its centroid is d[SUP]3[/SUP]/12). Since there are two vertical weld lines both d long, their combined MOI is 2d[SUP]3[/SUP]/3, which then must be modified to obtain the MOI about the centroid of the entire section by applying the PAT. [/QUOTE]
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Second Moment of Area calculation?
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