×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Weld Analysis for support hitch

Weld Analysis for support hitch

Weld Analysis for support hitch

(OP)
As shown in the attachment I have a hitch which will be welded to a 1/2" plate.  The max force the hitch would see is 1500Lbf.  The position of the force will induce a bending moment.  I have been going though my Shigley's book and the attached calculation is what I have come up with.  I am really unsure if it is even close to being correct.  So I was looking for some feed back as to if I am on the right path or not.  The hitch is to have a 1/4" fillet weld around the base.  So I calculated the moment of inertia of the weld using the line method as described in Shigley's.  My first question is do I need to rotate my bending stress element using a Mohr's circle like I did prior to adding it to my stress caused by the tension force or do I just add the two and do a Mohr's circle only once?  My next question pertains to the base material.  I know the allowable is 0.4 * the yield strength of the material but what area do I use, can I use the full leg of the weld or do I use the throat?  And then what force do I use, do I do a P/A+MC/I?  I have asked these questions to some of the guys I work with but they always use some rule of thumb fillet size and never question it, where as I want to fully understand it.  Any help is greatly appreciated.  Thanks in advanced.

RE: Weld Analysis for support hitch

(OP)
desertfox,

Thanks for the response; I like your methodology it's simple and easy to understand.  When I get into the office tomorrow I will give it a shot.   

The use of the Mohr's circle came from my Shigley's book.  From what I understand it assumes that the weld should fail in shear, along the throat plane.  Therefore you calculate your stresses and put them into a Mohr's circle to get your max shear stress.  Then you compare that to 0.3 * Su (Ultimate Strength) of the filler material.  I got the allowable (0.3*Su) from some AWS standard.  

Have you or anyone ever seen a weld calculation done this way?

Thanks

Bricklayer
 

RE: Weld Analysis for support hitch

I'd check (double-check ?) your assumptions of a load.   

You're using 1500 lbs as a load on a "hitch" - as if it were a trailer or towing (pulling) point.

Are you comfortable with that (maximum) load - a steady pull on a known  load (like a come-along or chain fall) is (somewhat) predictable - as long as the mechanic obeys your posted load limit sign at least.  

(A library shelf would be predictable too - until somebody climbs the shelf to put a book away on the top.....)

But a trailer hitch on the road or shop conditions should allow for "g" forces from shock and bounce - even unexpected ones like hitting a curb or hole that might easily triple your "normal" tongue and pulling weight.

RE: Weld Analysis for support hitch

(OP)
racookpe1978,

That 1500 lbs load is the load considering "g" forces and shock.

Thanks

Bricklayer

RE: Weld Analysis for support hitch

Not to muddy the water, but I spend half my time thinking about what I'm welding to.
If its a 2.5 inch square tube then the ~1.25 inch long welds inline with the top and bottom sides of the tube are the only ones capable of transferring much of the load.

I suspect the gusset that appears here above the receiver resulted partly from that concern.
http://www.etrailer.com/mm5/graphics/00000001/ct/31367_2_500.jpg

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources