- #1
nrobidoux
- 25
- 0
I wanted to pose a question here. It's based off a real world situation that I witnessed and was wondering what some people had has opinions (... or good reasoning/math). There is a 27-ton crane which has four outriggers to distribute weight and a rear stabilizer (similar to outrigger in appearance but holds little weight in comparison). The two outriggers in front are 90°, coming out horizontal then going vertical. The rear outriggers form an isosceles triangle (in ideal conditions) with probably... 45° angles at the base. When rigged properly, the wheels are not touching the ground.
Now what happened is that no one noticed for some time the retaining pin on one of the feet of the rear outriggers had moved out enough so only one end was through the hole on the foot. (A retaining clip somehow went missing.) The hole on the other side of the foot was misaligned from the hole in the outrigger by ~0.5".
Of course this was fixed right away but then the blame game happens and people want to place themselves as far away as possible from it. So there are two schools of thought on this...
One, the wind, which side-loaded the crane one day, caused it to rock back and forth, somehow torqued up outrigger (the only way I can see the pin move) and it worked its way out. I don't particularly believe this to be the case... I just did a quick search for frictional force to remind me of the equation... even if 1 ton of force remained on the ~2 in^2 of area on the pin... it's still a lot of force from the side to move the pin! Yes?
Two, my theory... the worker who drove the crane and arrived late on site admitted to driving fast for road conditions on a gravel road with many minor... and major bumps, washboards, and dips. This shook the 50 pound-ish foot around and wiggled the pin... not necessarily out (but that's my stance because these workers are into fast rig ups and can easily miss details like these). Just close enough to it (say if the tapered area at the pin's end was holding up that side of the foot) where the application of a lot of weight (rigging up the crane) or quick changes in weight (rocking back and forth in the wind) finished moving it out.
Thx.
Now what happened is that no one noticed for some time the retaining pin on one of the feet of the rear outriggers had moved out enough so only one end was through the hole on the foot. (A retaining clip somehow went missing.) The hole on the other side of the foot was misaligned from the hole in the outrigger by ~0.5".
Of course this was fixed right away but then the blame game happens and people want to place themselves as far away as possible from it. So there are two schools of thought on this...
One, the wind, which side-loaded the crane one day, caused it to rock back and forth, somehow torqued up outrigger (the only way I can see the pin move) and it worked its way out. I don't particularly believe this to be the case... I just did a quick search for frictional force to remind me of the equation... even if 1 ton of force remained on the ~2 in^2 of area on the pin... it's still a lot of force from the side to move the pin! Yes?
Two, my theory... the worker who drove the crane and arrived late on site admitted to driving fast for road conditions on a gravel road with many minor... and major bumps, washboards, and dips. This shook the 50 pound-ish foot around and wiggled the pin... not necessarily out (but that's my stance because these workers are into fast rig ups and can easily miss details like these). Just close enough to it (say if the tapered area at the pin's end was holding up that side of the foot) where the application of a lot of weight (rigging up the crane) or quick changes in weight (rocking back and forth in the wind) finished moving it out.
Thx.