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Re: Investigating Welds

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Dennis,
 
I agree with Neil Moore that you should work this issue with the people who will actually do the testing.  If you contact one of the larger area labs, you should find that the have a P.E. with expertise in materials testing whom you can discuss the issue with.
 
The testing procedure will vary with the configuration, location and accessibility of the weld, but the standard NDT (non-destructive test) technique for full and partial penetration welds is ultrasound.  X-ray is very expensive in comparison and mag-particle doesn't really tell you much about anything except surface condition.
 
For a voluntary test you can do whatever you want in terms of sample size, but you might want to use the SAC guidelines for moment frames as a clue -- I would think that a relatively small initial selection would be appropriate (10%?).  If those all prove free of defect then you can probably leave well enough alone.  If not, you repair the defects and test more, maybe another 20%, etc, etc, etc.
 
I have designed stagehouse fly galleries and rigging bridges for fully rigged stages and if this is a small to moderate sized theater I think your fifty kip total counterweight reaction sounds heavy. I recall designing typical battens (the bars from which the lights and scenery are suspended) for total loads on the order of a ton or so, with maybe a couple of heavier lines set-up for things like the main (fire rated) curtain, which is typically the heaviest thing they've got to support -- twenty five simultaneously suspended loaded battens is a lot.    It is possible that your stagehouse is "over-rigged" (e.g., that it was designed to accomodate maximum rigging reactions less than those to which it is actually being subjected, and that the safety factors have therefore been compromised).  If you think this is a possibility (e.g., if you see signs that some of the rigging is not original), it would probably be worth your client's time and money to have them try and find a copy of the original design drawings so that you can verify that they're at least in the ball park.  If you're concerned about getting in to an area outside of your expertise, suggest that they hire a theatrical rigging consultant (there are a few firms that specialize in this stuff).
 
Just some (probably over-cautious) thoughts.
 
Drew Norman, S.E.
Drew A. Norman and Associates
Pasadena, California
----- Original Message -----
Sent: Wednesday, April 18, 2001 12:16 PM
Subject: Investigating Welds

I received a call from a local production theater (plays and performances). The call was from their master carpenter who job includes evaluating the safety of the sets and mechanical platforms. He was concerned as there is a counter weight system of more than 50-kips which is used to lift sets, curtains and platforms. He is concerned only because of what he has read regarding problems with welds. He suggested I come in to help create a program where welded connection can be tested and verified. There are no noticeable problems, but he is doing this as a preventative measure to insure the safety of the people on stage and behind the scenes.
 
What is the standard I should follow to evaluate the welded connections that support the 50-kip counterweights? What percentage of welds should be checked? Should they be X-rayed, magnafluxed.....?
 
Any advice would be greatly appreciated.
 
Dennis S. Wish, PE

Regards,
Dennis S. Wish, PE
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