Joint design for structural tubing
Joint design for structural tubing
(OP)
I have come across a joint with an approved design for its application but I would like to learn more about my doubts.
The joint is a mitered joint between two pieces of structural tubing. Instead of butt welding the ends together a 1/4" filler plate is placed between the two ends and a fillet weld is used to join each piece of tubing to the 1/4" filler plate. A picture is available at http://weldinginspectionsvcs.com/TubingFitupQuestion.htm
My questions are
1) Is the filler plate tensile strength lower in the through thickness direction than the nominal strength of the plate.
2) Can the residual stresses from welding cause residual stress in the plate greater than would normally be encountered in a "typical joint".
3) Has anyone encountered this type of joint before. And wht type of service.
Any refernces to papers or publications for supporting documentation/research would be appreciated.
G Austin
The joint is a mitered joint between two pieces of structural tubing. Instead of butt welding the ends together a 1/4" filler plate is placed between the two ends and a fillet weld is used to join each piece of tubing to the 1/4" filler plate. A picture is available at http://weldinginspectionsvcs.com/TubingFitupQuestion.htm
My questions are
1) Is the filler plate tensile strength lower in the through thickness direction than the nominal strength of the plate.
2) Can the residual stresses from welding cause residual stress in the plate greater than would normally be encountered in a "typical joint".
3) Has anyone encountered this type of joint before. And wht type of service.
Any refernces to papers or publications for supporting documentation/research would be appreciated.
G Austin





RE: Joint design for structural tubing
The filler plate would not be as much of a concern as the effecience of the fillet welds vs typical full penetration V joints.
The stuctural integity question requires more information like tubing thickness, material, weld size, material ect.
Cheers
RE: Joint design for structural tubing
Rod
RE: Joint design for structural tubing
(2) Residual stresses will result from welds both sides, but should be no greater than normal. Look at the joint from the other way, and you have a pair of 5/16" fillet welds onto a 1/4" web. Nothing strange about that. Residual stresses don't affect the ultimate strength of "good" steel. If your plate was 1.5" thick, then I would be cautious about through thickness properties and residual stresses. Remember it all comes from billets 10" thick. Rolling down to 1.5" doesn't dispurse the defects nearly as much.
(3) A plate through the common plane of two sections with mitre cuts is one of the standard methods of making the moment joint where a building rafter meets the column. I use it regularly for such joints with RHS sections. I usually make the plate thicker - say 3/8" for 1/4" wall.
Reference Material: Being Australian, I have access to the Australian Institute of Steel Construction publications. I recommend their "Design of Structural Steel Hollow Section Connections", or "Design of Structural Connections". Try www.aisc.com.au - they might airmail them to you.
Russell Keays
RE: Joint design for structural tubing
The short - hand advice in their pamphlet "Design of SHS Welded Joints" is that provided that the thickness of the plate is 1.5 times thicker than the tube wall thickness, then the joint will be 100% efficient.
Regards
Andy Machon
RE: Joint design for structural tubing
Gerald Austin
http://www.weldinginspectionsvcs.com