How do I design a weld for stiffening a beam?

[zstructural]

I have a beam (tube) where I'm welding a smaller tube to the bottom to stiffen it up. Does anyone have any good resources explaining the method of designing the weld?

Thanks!

 

[slickdeals]

Are you placing the smaller tube inside the larger tube?

 

[zstructural]

The smaller tube will be welded to the bottom of the existing (larger) one. It's a new 4X4 welded to the bottom of an existing 12X4.

 

[IceNine]

Look up 'Shear Flow' in your Mechanics of Materials book.

 

[zstructural]

I don't have that book anymore, unfortunately. Is there anything online that might have a design example?

 

[slickdeals]

A sketch of what you are trying to do will help.

 

[delagina]

if it's just a few feet, just weld continously. it will be more than enough.

 

[slickdeals]

@delagina:

if it's just a few feet, just weld continuously. it will be more than enough

I don't mean to criticize, but I could not resist. You have a fellow engineer who is probably trying to design something that he has not designed before. It is our role, as a group of engineers with a variety of experience and skill set, to help him/her understand the mechanics of the problem.

We do not know what kind of loads we are dealing with or any detail regarding the problem. Just saying weld a few feet and it will be fine is a bad response. We all try to set really high standards in the forum. I am sure you understand.

 

[a2mfk]

I agree with Slick.

Zstruct- your question is too vague, we need a sketch of your configuration, show us the supports and the loads.

 

[zstructural]

The beam is 20 feet long, so welding continuously on both sides isn't rational.

I'm capable of designing the skip-weld once I determine my loads. I've done this before, but it was a long time ago, and I can't remember the shear flow procedure. Is it as simple as determining the shear/ft along the "joint" (where the two tubes meet), and designing the weld for that force? If so, I need to refresh my memory on how to calculate that force.

As for a sketch, just picture a 12X4 tube, 20' long, with a 20' long 4X4 welded to the bottom of it along its length.

Thanks in advance for the help!

 

[delagina]

ok noted.

you may use this excel as a reference

just like everybody said it's about horizontal shear.

 

[DWHA]

zstructural,

You should really look into obtaining a mech of materails text. It will be a valueable asset through out your career. Particulary it will be of value for this issue.

As for now, find someone with a mech of materials text and look into shear flow.

 

[csd72]

weld shear =VQ/I

 

[slickdeals]

See attached. I assumed a 3/8" wall. Others can check/verify the calcs.

 

[engotengot]

you also need to calculate "anchorage forces" at the ends. you will have a continous weld at certain length at the ends.

 

[zstructural]

Delagina - thanks so much for the spreadsheet! Unfortunately it doesn't address my unique situation, but that is an EXCELLENT resource to have for the future.

Slickdeals - thank you for your calc! that was above and beyond the call of duty. That does make it as simple as I was hoping it might be, and you answered my question completely.....that is until I read the next post about anchorage shear

engotengot - Is this a different "animal" altogether, or are the "anchorage forces" merely the larger shear forces near the ends? i.e. are you saying I might have 2 feet of continuous weld at the ends at the highest shear, and then skip weld between the two 2' welds at the ends?

Thanks everybody for your help. I REALLY appreciate it!

 

[csd72]

I believe what he is referring to is the transfer of the forces in the new section to the support.

If the stiffener stops short then these forces need to be transferred somehow.

 

[delagina]

if you will look at the excel spreadsheet there is the calculation for the weld at each end of the additional steel.
aside from the calculation of the interior stitch weld.

you dont usually add bottom reinforcement from support to support but only on location maximum moment where existing fail.