1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Moving retaining pin on 27-ton crane

  1. Jun 21, 2014 #1
    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.

  2. jcsd
  3. Jun 22, 2014 #2

    Simon Bridge

    User Avatar
    Science Advisor
    Homework Helper

    Sounds like one theory wants to say it is a no-blame accident and the other wants to claim some sort of negligence was involved. Unless the person responsible for setting the outriggers is being blamed?

    Both scenarios are plausible - without access to the situation or a proper investigation report there is no more to be said.
  4. Jun 22, 2014 #3
    You wrote
    These six words mean offer such a broad based time frame, and you can see the result with the blame-game and the production of ad hoc scenarios of the cause of the pin movement, which can lead to a not so healthy work environment if let to run its full course on its own.

    Instead, perhaps, a focus on a setting up of a walkaround inspection at regular intervals, inspections before and after shifts or change of crew, or some other procedure that could spot mechanical weaknesses before they could develop into a major problem. In other words, a check out that the equipment is in good working order before and during use.
  5. Jun 22, 2014 #4

    Simon Bridge

    User Avatar
    Science Advisor
    Homework Helper

    It's a good point and one I restrained myself from commenting on earlier. - rather than look for blame, work out a policy so it does not happen again.

    I don't want to second guess the existing policies or practices though... there is not enough information.

    i.e. It may be that someone was supposed to do an inspection to make sure everything was all right.
    From the descriptions - the truck driver may have been responsible for making sure equipment is delivered in good conditions and the person who positioned the outriggers may have been responsible for their safe and secure deployment. Maybe both slipped in their duty and the procedures around delivery and deployment need to be tightened up?

    Blame also comes into play when there are issues of liability.

    Part of good engineering is managing workplace policy.
    There should be work and safety policies in place - examine them.

    I don't think this is a mechanical engineering issue so much as a management issue, so pretty much out of scope for these forums. I support 256bits in that the production of these scenarios is not helpful... but you know that already.
  6. Jun 22, 2014 #5


    User Avatar
    Science Advisor
    Gold Member

    In the US and Canada, there are rules governing crane inspection - e.g.: OSHA 1910.179(j). These inspections must be documented at periodic intervals. If this happened in North America, it is almost certain somebody in management dropped the ball. I suspect EU has similar provisions.
  7. Jun 22, 2014 #6


    User Avatar
    Science Advisor
    Homework Helper

    From the OP's description, there was no "accident". This was an "incident", not an accident.

    If the crane was so poorly designed that one misaligned or poorly supported outrigger foot is a serious safety hazard, that is a completely different issue!

    I'm not familiar with the laws of your country relating to cranes, but it seems to me this should be perfectly straightforward. It is clearly somebody's responsibility to ensure any crane is safe before it is used. In the UK I would expect that person to be the crane operator, who might or might not be the same person as the driver when moving it between sites. Crane operators are are required to take formal tests, and are licensed to operate particular types of cranes.

    The issue of what happened to the missing retaining clip is secondary. The primary question is why nobody noticed it was missing.

    As for theories about what happened to it, don't ignore the "laws of human nature" one - another crane operator found that a safety clip was missing from his crane, "borrowed" a clip from another crane which was not in use at the time,, and "forgot" to do the paperwork to tell anybody about it.
  8. Jun 24, 2014 #7
    Thanks for the replies. As far as I can see the whole thing has blown over. It was fixed when spotted. It just bugs me that more than likely both shifts missed this detail (7 people in total) and the shift opposite me (who has the driver I mentioned as part of their crew) of course discredits my theory.

    To address your concerns about inspections.... yes, they are suppose to be done daily. Twice daily. One per shift. Sadly this does not happen. (And the main focus is on leaks. :?) As for the length of time, could've been like that up to 5 days. O_O Pretty sure it was more than one as there was little / no wind the day it was found. A coworker and I talked about it yesterday and mentioned how the crane sometimes moves back-and-forth in the wind. It made sense then... more so then side-to-side which is what I originally thought.

    I wish I could say my coworkers would pay more attention to these details in the future. I believe everyone knew what happened within an hour (gossip spreads faster here than in high school). I don't see a difference. I can only say that I will be paying more attention. I'm already the "observant" one and it is a little unnerving at times to see how much goes unnoticed.

    As for the responsibility it does fall on the crane operator.
  9. Jun 24, 2014 #8


    User Avatar
    Science Advisor
    Gold Member

    Someone in management should be responsible for ensuring inspection documentation is in order. The operator is frequently responsible for crane inspection, and well may be the only person actually qualified to do it, but, nobody is going to sue the crane operator if someone gets hurt and it turns out inspection documentation is missing.
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Similar Discussions: Moving retaining pin on 27-ton crane
  1. 90 ton impact absorber (Replies: 3)

  2. Power of the Crane (Replies: 1)

  3. Crushing Area Of Pin (Replies: 3)