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# Welding - Determine Unit Second Moment of Area (Iu)

## Welding - Determine Unit Second Moment of Area (Iu)

(OP)
Hello All,

I am working through some weld calculations and have a profile which is not covered in the standard "treat a weld as a line tables" for bending and torsion.

I am looking for the governing theory to determine the Unit Second Moment of Area (Iu)[Shiggley's notation] for bending is determined. I have a feeling this is pretty straight forward but I can't find any information, only the pre-calculated tables.

### RE: Welding - Determine Unit Second Moment of Area (Iu)

If you post up a sketch of your weld geometry and loading condition, I'm sure that with all of the knowledge on this forum we can get you an applicable theory and the design codes to back it up.

### RE: Welding - Determine Unit Second Moment of Area (Iu)

Well at the end of the line you can always use basic mechanics to determine things like that

### RE: Welding - Determine Unit Second Moment of Area (Iu)

cogmaster, I believe you would calculate the cross sectional properties for the line of weld the way you would for any shape, but use a unit value of 1 for the width of the weld. This will give you an inertia with units mm4/mm that will then give you a section modulus in units of mm3/mm, and when divided by your bending moment will give you a shear on your weld in units of kN/mm. I suggest using this method to calculate Iu for some of the shapes that have tabulated values and then compare your answer to the table.

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