Removing the bolts doesn't really have an impact on strength. A lack of a bolt can cause wear on a pin as the structure flexes, but typically unless you're leaving it for years that wouldn't be an issue. You can inspect the wear the next time you use the pin.
Removing pins weakens the structure substantially. However when the crane isn't in use, it doesn't need anywhere near all of it's strength, so removing one of two pins is fine.
I would guess in this case, they removed 2 of 2 pins, leaving gravity the only thing holding everything in place, which is plain stupid.
Simply loosening bolts to “hand tightened” has led to crane collapses. (The article under the Worthton accident on page one summarizes expert witness testimony to this effect)
In general, removing even one element from a truss structure substantially lowers safety margins. Also, crane collapses often happen during assembly and disassembly, since that is when unexpected things often happen. Unnecessarily removing redundancy from the structure increases the chances of such collapses.
Can you explain the difference some more? I think of a bolt as a pin with threads, that gets secured with a nut on the other end. A pin has no thread and gets secured by putting another piece through a hole in the end of it.
So they have different failure modes (a bolt can get its thread stripped, or vibrate the nut off) but otherwise can be used interchangeably. What's the structural difference you are referring to?
Right. Bolts are usually weak in shear but strong in tension.Their job is to create high friction between two pieces; that friction joins the two pieces as one.
I believe the metal sleeves that the bolts go into are the pins.
Edit: I probably shouldn't have said "sleeves". That has more than one meaning in this context. I'm talking about hollow pins, secured by bolts when I say "sleeves".
I think it's right. He seemed to be describing hollow pins with threaded holes. The pins hold the sections together, the bolts screw into, and steady the pins.
Watch this video for a good breakdown of what people think happened: https://www.youtube.com/watch?v=cexN2-T6dxY&feature=youtu.be he has a followup video with additional pictures sent in from the scene that seems to corroborate his thoughts
Removing the bolts doesn't really have an impact on strength. A lack of a bolt can cause wear on a pin as the structure flexes, but typically unless you're leaving it for years that wouldn't be an issue. You can inspect the wear the next time you use the pin.
Removing pins weakens the structure substantially. However when the crane isn't in use, it doesn't need anywhere near all of it's strength, so removing one of two pins is fine.
I would guess in this case, they removed 2 of 2 pins, leaving gravity the only thing holding everything in place, which is plain stupid.