Sq. Tube Lap Joint

Date 05-27-2003 15:47

I'm not a train driver(engineer), but I will offer this........I think it is permissible as long as the welds are not tied together to the welds in the opposite plane. If you are working to D1.1:2002, look at figure 2.8 and paragraph 2.8.3.5
Also the Commentary on this states it as someone trying to cover up for poor fit-up.
John Wright

By Distilled (**)

Date 05-27-2003 16:03

I've gotta track down my darn D1.1 here and check out that figure - -

My ol man is a Mech. Eng. so this isn't really his field of expertise but he said he had heard of crystalization occuring at the toe of the weld when welding across sq. tube like that but said it had been a while and couldn't give me any explanation.

The story I had heard is that the weld, located where I had tagged "No Weld", takes up all the stress and load transferred through that joint rather than letting the load span over the two longer welds on each side. I know that when I had welded up a number of production parts one time with a configuration similiar to this the Engineers almosts scrapped the whole batch of them rather than letting them slide.

Herm, anyway, thanks a bunch for the reply John and I'll take a look at that figure and paragraph for reference. Have a great day!!

BJ

By jwright650 (*****)

Date 05-27-2003 16:29

I stated (typed) that wrong, it's do not tie the welds together when you have "fillet welds on opposite sides of a common plane".
John Wright

By CHGuilford (****)

Date 05-27-2003 20:52

I think you might find the main reason for not connecting welds from "opposite sides of a common plane of contact" is that where the welds join, or "wrap" together, it is difficult to get the full weld profile there. Considering that joints like that would start to tear at the corners, welds with low throat would certainly be a problem.

CHGuilford

By Distilled (**)

Date 05-28-2003 09:39

Excellent point and it it awfully difficult to make a corner such as that would be and not leave some significant undercut/undfill defects.

The rumor that I had heard in the past was that not puting a weld there had something to do with how the member transferred loads I thought but I may be mistaken - any Welding Engineers out there?!?! :)

Thanks for the replies guys!!

By Niekie3 (***)

Date 06-01-2003 20:40

Hi Distilled

I believe that we are talking about two different things here.

Firstly the issue that was raised about the weld not "hooking around" to another side on a common plane of contact, is due to the almost certain weld defects and lack of leg length that will be obtained, along with the fact that it makes inspection of the fit-up essentially impossible.

The second issue that I believe you were concerned with all along is whether to allow a weld on the "overlapping" side of your joint. (Without hooking around.) I believe that it will depend on your particular circumstances, and that indeed it is an issue of "force flow" from one member into the other.

If your square tubing had a wall that was thick compared to the flat plate, then there would be little wrong with placing a weld in this position, because the rigidity of the tubing would allow the force to be transferred through all the welds of the assembly. This situation is however unlikely, because the square tubing would typically have a much thinner wall.

Under this situation, (the thinner wall) the force flow would be concentrated through the weld on the "overlapping" side, as a tensile force. This would result in a great stress concentration, and would weaken the design. By placing the welds along the sides and end of the connection, you introduce a much larger area through which the force is transmitted by shear.

Hope this helps.

Regards
Niekie Jooste
Fabristruct Solutions