# Calculating weld stress under bending load using Shigley?



## Shaggy

Hello,

Does anyone have experience calculating the stress in a welded connections that are under a bending load? Specifically using the techniques outlined in the Shigley Mechanical Engineering Design. These techniques represent the weld as line.

On page 397 of Mechanical Engineering Design (5th edition), Shigley has a table that lists the Unit Second Moment of Inertia for a weld treated as a line. My understanding of the use of this table is to mulitply the Iu in the table by .707(h) to get the actual I, h being the weld size. The .707 is the proportion of the leg length to the thickness of the fillet at the throat. The .707 is initially described on page 392 (equation 9-7) dealing with J for a torsional load on a welded connection. This is the first use of that type of table (treating the weld as a line). The sample problems in Shigley all use this .707 in these types of problems. Unfortunately the homework problems in Shigley for bending welds don't list answers.

I have done some practice problems (in the "the other board" sample exam and practice problems books) that use different techniques. When I use the Shigley techniques as described above, I get different answers than those in the practice problems. I don’t know if I am applying the Shigley table properly.

Any help is appreciated,

Shaggy


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## Shaggy

For a pretty good discussion about the above topic (with some good links), check out the thread I started on Eng-Tips. For those of who may not be familiar with Eng-Tips, it is a pretty solid engineering message board.

http://www.eng-tips.com/viewthread.cfm?qid=183717&amp;page=1


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## JohnNevets

Gee Golly Shag,

Now I feal a bit silly. Last night I took about 15 minutes to write up a nice long description of how I do welds, but that they were all based about using the force/in method. However after reading my post I realized, that it probably would just confuse you more since you were trying to use Shigley and I use Blodgett's "Design of Welded Structures"as a guidline. By the way if you do much weld design this is a great book, all beit quite old, Lincoln welders sells it dirt cheap for what you get. So when I remebered there were others on here that did use Shigley, I just deleated my post. Now I read the response you got on the eng-tips, and they sent you down the same path.

As me and metro usually respond around here it is very important to know the basics, before using the plug and chug methods. However, chances are very good that if you see a welding problem on the PE, it will be a fillet weld, so it may be helpfull to remember how to use the .707*h factor for your throat I see on the other forum, they are letting you know about other types of welds as well, this is great, but know your fillet welds well, for us ME's that is typically what we see, SE's on the other hand need to know it all.

I'm writing this at work so I'm on a bit of time crunch, and no spell checker, so please ignore the poor proff reading.

Hope that helps some, jsut wish I had followed through last night,

John


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## Shaggy

Thanks for the info John. I happen to own the blodgett book, design of weldments, but do not own the design of welded structures. I plan to pick that one up. Thanks for also verifying the .707 factor for the fillets. My review instructor got back to me with an email corroborating the info.

-Shaggy


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