Capacity of a round weld 2

[anchorengineer]

Hello All,
I'm looking for a formula to calculate the capacity of a fillet weld for a round post with a horizontal load at the top inducing a moment.
Thanks!

 

[KootK]

This, my friend, is the thread for you: Link. It's pretty fresh too.

The greatest trick that bond stress ever pulled was convincing the world it didn't exist.

 

[spats]

See the attached. Simply calculate the section modulus of the weld, treating it as a line of unit width (line properties) with a diameter equal to the outside diameter of the round post. An M/S calculation will give you a lbs./per inch bending stress (S is in units of inches squared). Then take the horizontal load and divide it by the length of the weld (pi*dia.). The resultant load on the weld is the square root of the sum of the squares (bending stress is perpendicular to the weld; horizontal stress is parallel to the weld). Compare the resultant maximum stress to the allowable lbs. per inch of your weld.

 

[desertfox]

try this

http://www.roymech.co.uk/Useful_Tables/Form/Weld_strength.html

 

[KootK]

Then take the horizontal load and divide it by the length of the weld (pi*dia.)

I question this spats. The shear stress in the member will be concentrated in the portions of the tube wall most parallel with the applied load. As a result, I believe that the same will be true of the welds. Of course, the shear load impact on the welds is likely to be insignificant unless the pipe is very short.

The greatest trick that bond stress ever pulled was convincing the world it didn't exist.

 

[spats]

If you want to question it, I suggest you contact Lincoln Electric. However, I doubt that Omar Blodgett is still around. My dad used to work with him, and my dad is 91 years old.

 

[KootK]

If you want to question it, I suggest you contact Lincoln Electric. However, I doubt that Omar Blodgett is still around. My dad used to work with him, and my dad is 91 years old.

I hope that Omar is still around. I thought that he was still contributing to

http://www.weldingdesign.com.

Either way, I see no need to bother him with this.

While I can't claim a family connection to Blodgett, I'm enough of a fan that I own hard copies of absolutely everything that the man ever saw fit to put to print. If you can point to an example in any of Blodgett's works that supports your method, post a reference to it. I'll run down stairs lickity split, scan it, and post it here for discussion.

Alternately, if you're up for it, we could just debate the issue using our collective understanding of structural behavior.

The greatest trick that bond stress ever pulled was convincing the world it didn't exist.

 

[CELinOttawa]

Omer. Not Omar... The old southern US name, not a Muslim name...

Not that it matters in particular, but if you're trying to find one of his (excellent!) books, you might want to use the correct name...

 

[CELinOttawa]

Oh, and re this:

Alternately, if you're up for it, we could just debate the issue using our collective understanding of structural behavior.

Let's all try to play nice...

 

[spats]

Pretty picky! Blame my IPad voice recognition. By the way, I attended "Omer's" weld design seminar in Cleveland in 1972. I traveled half way across the country specifically to see him. As I said, my dad worked with him... I want to say it was the late 40's or early 50's. At that time, they were both involved in the seminars. Of course, Omer was the design guru. My dad is a mechanical engineer, and was more of a welding procedures and equipment guy.

 

[KootK]

@CEL: Challenging someone to a technical debate on a technical forum is not unkind is it? I'm sure spats' ego can handle it. I know mine can if it turns out that I have to eat crow on this one. It wouldn't be the first time. In fact, it wouldn't even be the first time this week.

Picking on spelling mistakes on the other hand... that's just pretentious and annoying. I type on my phone damn it; stop picking on me.

Instead of playing nanny / referee, why not step up to the plate and share your thoughts on the issue du jour?



The greatest trick that bond stress ever pulled was convincing the world it didn't exist.

 

[spats]

I apologize if I pushed your button KootK. I didn't know if you were looking for a fight, or trying to stimulate discussion. I guess I have a little arrogance in me, like most structural engineers I know.

 

[CELinOttawa]

Haha... I have no thoughts, having thoroughly wacked my head on some ice while leaving the office.

It is a fine ER visit for me to end my "wonderful" week of tummy bug. *sigh*

And I did not mean to be pretentious or difficult, just pointing out the correct name for one of our living legends. Respect, that is all.

 

[KootK]

I'm neither offended nor seeking a mean spirited brawl spats -- no apology required. I've been learning from you for years now and I know that a) your opinions are not to be taken lightly and b) you can hold your own in a debate. I'm confident that you're wrong here. I simply want you to agree with me or straighten me out such that I agree with you. It's part of my education as an engineer.

I wish that there were a warm & fuzzy emoticon for "I love you dude... but I think that you're frickin' out to lunch on this one".

The greatest trick that bond stress ever pulled was convincing the world it didn't exist.

 

[KootK]

@CEL:

First rule of eng-tips club... we talk about eng-tips club.

Second rule of eng-tips club... we TALK about eng-tips club.

Third rule of eng-tips club... if it's your first comment on a thread, you have to weigh in!

Get healthy, come back Monday, and answer the question damn it!

For anyone not getting the pop culture reference, these are not actually the rules of eng-tips club.

The greatest trick that bond stress ever pulled was convincing the world it didn't exist.

 

[medeek]

Here is a calculator that can basically do that and a little more:

NPW Weldcheck

A confused student is a good student.

 

[medeek]

and yes this utilizes the methods of Blodgett.

A confused student is a good student.

 

[KootK]

Oh me, oh my... I fear that I shall have no digi-buddies left by the end of the night.

@Medeek: I love you dude... but I think that your software is out to lunch on this one. I think that it suffers from the same error that spat's method suffers from IMHO.

Your fvy and fvz values are constant at all locations. That would be appropriate for a solid shaft where the weld group could be expected to move as a singular, rigid body. However, for this problem where we are dealing with a hollow shaft, I would expect the fvy and fvz to vary about the weld group.

It's quite similar to the situation with a wide flange section. If we applied a strong axis shear to that section, we would not expect the fyz values in the flanges to match the fyz values in the web. Rather, we'd expect the bulk of the shear force to be resisted by the web and relatively little to be resisted by the flange shear stresses. It's the same with a rectangular HSS and similar with a round HSS.

@Spats/CEL/Medeek: please note the change to my signature.





The greatest trick that bond stress ever pulled was convincing the world it didn't exist.

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 that I want to either change it or adopt it.

 

[Ron]

No, No, No!!

Half of the post is in tension and half is in compression....it is a couple from the moment.

For the half in tension, the weld is in shear....typical fillet in shear....1/2 the circumference taking the tension of the couple (the compressive portion of the couple can be neglected).

Now you have to consider that the horizontal load must be resisted in shear. The whole circumference resists this. You now have a combined stress in two directions. You can consider them independently, but you have to check the resultant of the vertical and horizontal vectors across the throat of the weld as well.

 

[medeek]

You might be onto something with what you are saying. The problem is how to quantify this. I'll have to crack open my ME book to think about this some more. This would be a good candidate for FEA.

However, if you apply a simple thought experiment perhaps it might become more clear. Assume we have a hollow pipe welded around its perimeter, at the other end of the pipe we have a load evenly distributed around the pipe perimeter that is perpendicular to the pipe's long axis. Now imagine that we slowly decrease the length of the pipe until it is almost zero length, everything else remains the same. You would find that the shear load around the perimeter of the pipe is now evenly distributed along the weld. There may be a flaw in this thought experiment but for now it makes sense to me.

A confused student is a good student.