Clip/Lug calc on Non-rectangular shapes

[kwbtkc]

Can COMPRESS perform a Clip/Lug calculation on a Non-rectangular attachment such as a channel shape?

Thanks!

 

[eeromatti]

Compress does not calculate the lug itsef but stresses in shell caused by loads on lug. That's why shape of the lug is (almost) irrelevant. If you are interrested in stresses of the lug itself use basic strength of materials or FEA.

I don't understand what "channel shape" but if you give us an explanation or picture (!!) it would help a lot. If it means that lifting lug is attached to shell with two separate welds you should be able to calculate lifting lug attaching a reinforcement pad (thick enough) with width equal to distance of the attachment welds of actual lifting lug. Just make sure that distance from shell to load is correct to get moments calculated right.

 

[kwbtkc]

Yes. I meant the stresses in the vessel shell itself, not the lug. I have an existing C8 x 11.5 that is welded directly to the vessel wall with no repad. Maybe the way to do this is to convert this shape to a rectangle. It seems like there was a set of formulas in The Pressure Design Manual to do this.

Thanks.

 

[jte]

eeromatti-

A channel section is a type of extruded structural shape most often used for relatively light beam applications:

http://www.engineersedge.com/standard_material/Steel_channel_properties.htm

In particular, a C8x11.5 (ie a Channel section which is nominally 8" high and weighs 11.5 lbs/ft) is probably the most commonly used structural shape for vessel platforms in the USA. What's a bit unusual is that the channel is usually bolted on to a rectangular clip cut from plate which is welded to the vessel. I've rarely seen structural shapes welded directly to the vessel...

jt

 

[TomBarsh]

COMPRESS analyzes the local stresses in the shell at the attachment using Welding Research Council bulletin 107 ("WRC-107&quot. The bulletin has limitations on its range of applicability, depending on a number of geometric parameters. The biggest limitation is that the bulletin addresses circular and rectangular (and square) attachments only. Thus the WRC-107 analysis cannot determine stresses in the shell for a complex shape such as a channel, wide flange, etc.

In my experience, "good practice" would dictate attaching structural sections (for piping, platforms, etc) to the shell by a bolted or welded connection to a pad plate or tab as jte describes. But this may not always be the case and a more sophisticated analysis may be warranted.

Nozzle Pro (All Pro) finite element analysis software from Paulin Research Group (

http://www.paulin.com)

provides a number of templates for structural attachments to the vessel, permitting a relatively simple method for performing the finite element analysis. Nozzle Pro includes templates for structures such as channels, wide flanges, and many other shapes.

Tom Barsh
Codeware Technical Support