Pipe support bkt clip + WRC-107

[picasa]

If for a 0.5" thick and 6" long pipe support bkt clip, WRC-107 calcs come out with 4" wide pad req'd, can you take credit for all of that pad? Or anything beyond 3" wide is not useful?

 

[warrenw]

The way I interpert a bracket design is this way;
1.) The bracket has a weld line cross section (or foot print) that transfers the load to the vessel. In your case you have a foot print that is 1/2" wide and 6" long.
2.) If the stresses from the bracket foot print are too high then the foot print has to be increased (add pad).
3.) The pad width and length are sized so it's foot print on the vessel is large enough to bring the stresses at the weld line to the vessel's allowable range. WRC-107 checks the stresses at the bracket foot print assuming the vessel thickness and the pad thickness are acting as one combined thickness.
4.) The pad has to be checked to make sure it is strong enough to transfer the load from the bracket to the pad outside weld line.
Inother words, if the pad needs to be 4" wide and is only 1/4" thick, it may fail in bending between the bracket and the pad outside edge where the weld line is.
I'm going from memory right now but I don't think WRC-107 checks the pad thickness for this load case, it assumes the pad is adequate to tranfer the load to the weld line.

 

[picasa]

In this analysis, what are the typical values used for stress concentration factors Kn and Kb?

 

[warrenw]

Pressure Vessel Design Handbook by Bednar says Kn and Kb may be taken as equal to one.