Top head lifting lug as per MOSS 4th ed - Problem with units

[VPbris]

Hi guys,

I'm building a Mathcad sheet for designing top head lifting lugs using the method on Pressure Vessel Design Manual - Moss 4th ed. I am having some trouble with the units.

On page Procedure 10-6 (page 693), when calculating the Pad Eye Weld, i'm getting strange units.

the formulas are

f4 = Pt * tp * pi * D2 / (2*tp + tl)

w3 = f4 / (0.707*Fs)

where f4 is called unit shear load on pad

Pt is the load on transverse direction
tp is the pad eye offset from the lug plate
tl is the lug thickness
D2 is the pin diameter
Fs is the allowable shear stress

I'm getting N*mm unit for f4 and mm³ for w3. Any ideas? I tried using Fs as N/mm (using weld strenght but unit is still mm²).

 

[SnTMan]

Agree, f4 is N*mm. Wouldn't Fs be N*mm^-2? Giving 1/mm^-1 (or mm) for w3?

Regards,

Mike

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[VPbris]

If Fs is N*mm^-2 w3 would be mm^3

 

[SnTMan]

Apologies, arithmetic failing me this morning. But, I don't see a term for weld leg dimension? Or is that w3?

I don't have the Moss reference, nothing further to add...



The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[VPbris]

No problems!, Yes, weld leg is w3