Rigging Analysis : Tail Lug OverStress

[CBernard]

I'm designing a tower 74" ID and 71' 3" S/S. I'm trying to use the rigging analysis "tail lug" attach feature, and using my clients standard tail lug detail. I'm getting failure and the error "The load ratio for the EN13445 calculation exceeds 1.Lift load 122,627 lbf exceeds maximum allowable load 26,701 lbf." for EN as well as WRC 537 "The local stresses in the WRC 537 calculation are excessive."

The lug design calls for the lug to be between the bottom and upper base rings, with continuous welds along the shell, upper base ring, and lower base ring. Based on the diagram in compress, it looks like there is only a continuous weld on the component you are attaching to (in this case the base ring).

My question is there any way to account for the actual strength of this situation in Compress, and not just the worst case localized to the base ring? I can of course run an FEA, but was hoping to keep it in the compress model.

Any help is appreciated.

Thanks,

 

[TomBarsh]

Sounds like the lug is supported (welded) on 3 sides and that a local stress analysis of the shell is not required. Nor would the analysis using WRC 107/537 or EN 13445 be appropriate for this because these analyses do not consider the effect of adjacent structural support (nor their stresses). You'll get a lot of support for the plate (lug) with it attached on 3 sides. The last I saw the COMPRESS tailing lug dialog lets you select/disable the local stress analysis. I think even a Warning is produced in the Deficiencies/Warnings report that the local analysis may be overly-conservative.

Did you try contacting Codeware technical support? My understanding is they were in the direct path of hurricane Irma but that they are still in business.

 

[CBernard]

Tom,

No I haven't yet, but that may be my next step. I did see the note you're referencing in the deficiencies, and definitely agree it's one of those the gut is saying it's fine but want to confirm via the software. I was hoping to not have to turn off local stresses, but that may be my best option.

Thanks for the help!