Design help
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Posted by: chris.tucker ® 03/16/2010, 12:05:55 Author Profile eMail author Edit

I am trying to find out how to determine whether or not the side wall of a tube would fail or the welds would fail. I am basically building a bridge. I have two 5x5x.25 tubes that are parallel to one another about 36in apart with angle 3.5x3.5x.375 welded between ever 6.5in apart. I am not sure what calculations I will need. I am figuring with a safety factor that each angel will see about 30,000lb Could some one lead me in the correct direction

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: Design help
: Design help -- chris.tucker	Post Reply	Top of thread	Engineering Forum

Posted by: Pinkerton ® 03/24/2010, 21:28:20 Author Profile eMail author Edit

Chris, For 30,000-lbs, I think you are playing with big fire, but here goes anyway. If the welds are preformed by a certified welder AND they are not stitch welds, there will be more than enough welded-length to forget about the welds failing. You do not state a length of the "bridge." The 30K-lbs is a lot of load and without doing any calculations, I too would guess that 5" tube is way small for that load unless the bridge is about 3' long. As to the angle positioned as shown and at 30K-lbs, I suspect that would be marginal in strength too. You need qualified help for something that weighs 30K-lbs. Get a Structural Engineer to design it. Dave

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: Design help
: Design help -- chris.tucker	Post Reply	Top of thread	Engineering Forum

Posted by: Paver ® 03/17/2010, 09:50:16 Author Profile eMail author Edit

I'm not sure exactly what your application is here but with the loads you are discussing and the word "bridge" involved I would HIGHLY recommend that you have a structural engineer assist you with your design. Much more to look at than just the welds. Bending stress for instance. Just a few back of the envelope calc's on my part lead me to think that you're cross members are very undersized for the 3' span and 30,000lb load. Depending on the length of your bridge, the 5" tube may also be too small. Again, please consult with an engineer. In the long run it will be far cheaper than the damages/injuries if something would fail.

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