Welding rectangular tube to circular pipe 1

[SPDL310]

For weld stress calculation purposes would a rectangular tube branch welded to a circular main member have more or less weld stress than a rectangular tubing welded to a flat plate?

 

[racookpe1978]

It depends on the joint geometry.

And that "geometry" means EVERYTHING about the joint:
angle of intersection,
wall thickness of the stock
plate thickness
assumed fillet weld dim's and fillet weld positions and all weld preps and their angles
diameters of the "pipe" and dim's of the tube steel
type of stress on the joint and loads and moments
vibration of acceleration factors
safety issues for the application
type of application and cyclic loads


Draw both.

Show both here as files.

 

[SPDL310]

Thank you for the reply. I'm sorry for being so late with a response. I will try to have the files posted by the afternoon. In the interim a better written description. The main branch is an 11.75 in OD pipe with a .5 in wall thickness with its axis running vertically. The rectangular tube in 7" X 5" with a .5" wall. It is mounted perpendicular to the main branch and used as a cantilever beam with the long axis of the tube running vertical. The tubing is made of ASTM A500-10 GR C. The pipe will be API 5L X56. The pipe will not hold pressure or contain any fluid. The angle formed between the rectangular tubing with the tangent of the circle at the weld is 115 degrees. The rectangular tubing will be machined to the contour of the pipe. I will post prep angles with sketches. Sorry if this is confusing.

 

[EdStainless]

Since it is rect the load directions are important. Where the short sides of the rect are fitted to the round you will have more weld joint than if it were a flat plate, but depending on loading this may not help you.

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P.E. Metallurgy, Plymouth Tube

 

[SPDL310]

Here are the pictures of the beam.

 

[SPDL310]

more pictures.

 

[SPDL310]

The first picture shows the loading points for the beam. the vertical turnbuckles will support a evenly distributed load of 4500 lbf. The angled turnbuckle will balance the moment about the weld at the farthest distance from the end. Those distance are measured in the picture. The expected loading is 8243 lbf along the shown vector. The final picture shows my proposed weld prep. The loading on the joint will primarily be axial compression but during the bolting procedure the joint will also experience a bending moment. in the completed configuration the expected magnitude is about 8300 lbf. The components supported by the beam are bolted to the structure but are supported by the beam to relieve a significant moment from their bolt group.

 

[SPDL310]

I forgot to include the angles for the weld prep. Psi would be 90 and Phi would be 45 degrees.

 

[KootK]

Given that the radius of your main member is quite large relative to the width of your beam, I would expect weld stresses to be comparable to those that you might see if welding to a stiff, flat plate.

At the loaded end of your beam, I would move your work point to the intersection of the plate and the top of the HSS beam. You'll have a bit of moment in the beam but a much more robust and predictable force teansfer mechanism at the connection. And you'll eliminate bending stresses on your gusset plate.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[SPDL310]

Thank you for the response. Unfortunately both lift points are pretty much locked where they are shown here by geometry demands. There was a clearance issue when the top pickup was next to the gusset plate. KootK would the bending still be an issue if a an extra gusset was added between the pickup point and the gusset at the end? Would it be better to cut the plate short and add an extra gusset with no connection to the gusset at the end?

 

[KootK]

I think that the second best way to do it is how you showed it originally. It's no big deal, just need to design for the forces and eccentricities.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[SPDL310]

Thank you I will add calculations at a later time to see if I am on the right track for eccentricity ect.