Part 6: Mobile Crane Stability – Don’t Be A Statistic

Monday, January 29th, 2018

When we began this series, we mentioned that tipping is the most common type of accident with cranes.  To that end, we are trying to do our part to keep you from becoming a statistic by providing education as you work in and around cranes. We’ve looked at how gravity, balance and leverage work together to keep a crane stable, how the crane is made, what the tipping point is, and what the standards and OSHA say. Now lets apply what we’ve learned.

They say a picture is worth a thousand words, so this post will use illustrations to indicate some of the various configurations and quadrants of operation where there may be stability concerns and include images of where something went wrong. Please remember, these are only examples and it’s important that you refer to the crane operator’s manual and the load capacity chart for specifics for your crane. We cannot stress the importance enough of taking the time and making the effort to ensure proper set up, knowing your load weight, and having an educated operator–it just might save you a costly mistake.

Lifting on Rubber

Crane manufacturer’s that allow “on rubber” lifts will provide a load rating chart specifically for this configuration.

In the image below, the rough terrain crane clearly did not have its outriggers extended and set.  It was simply overloaded and lost it’s stability, causing it to tip over.

 

Over the Side

truck crane2

Not only are fully set outriggers recommended for the full capacity of the load chart, the image to the right illustrates a telescopic boom truck crane with the boom over the side quadrant. Lifting over the side is the least stable location for most cranes.  For this reason, try to position the crane to make the initial lift in the least stable location (such as over the side), and then swing to a more stable location (such as over the end). This may help prevent an accidental overload of the crane during the lift. In other words, any miscalculation of the load weight can be noticed right away.

Over the Front

When the boom is positioned over the front of a crane on outriggers, the tipping axis is the forward set of outriggers. Crane manufacturer’s that allow “over the front” lifts will provide a load rating chart specifically for this configuration.


The rough terrain crane pictured above is an example of  the load’s leverage exceeding the crane’s leverage, as discussed in part 4. When the crane was overloaded it lost stability, causing the back outriggers to lift off the ground.

Over the Rear

When the boom is positioned over the rear of a crane, the tipping axis is the rear set of outriggers. While this is usually where the most capacity is provided, you must still follow the load chart, and know your load weight for your lift to ensure the crane will remain stable and upright.

In the image above, an oak tree was being removed from a residence. As the large trunk portion was being lifted, it proved too much for the crane and it tipped over the rear and split this home in two.

Boom Length

Just because a crane has a long reach, doesn’t mean you need to use all of it. Many times tipping is a result of the boom being extended beyond the necessary length.Crane-Tipping

In the case of this tipping accident below, they were only lifting an electric motor, however the outriggers were not set and the crane tipped over because the boom was extended beyond the capability of the crane. If the outriggers been properly extended and set, this lift could have been completed in a safe manner.  What should have been a simple lift, became a very costly one.

boomlength

 

Hopefully by now we can all agree that the loss of stability resulting in a tipping incident or accident shouldn’t be a common occurrence. They are costly and can be avoided.  Remember the following key points:

  • Make sure the operator is a qualified mobile crane operator with the education, knowledge and experience to operate the machine and make the lift.
  • There are many crane designs, read the crane manufacturer’s operation manual to make certain the operator fully understands the operating quadrants, superstructure positions and operating characteristics of the crane.
  • Make sure the operator fully understands the load capacity chart  for the crane they are operating.
  • Make sure the operator fully understands how to use the crane’s load weighing device (LMI, RCI, RCL, etc.).
  • NEVER lift loads where the load chart does not provide ratings.
  • NEVER lift more weight than what’s posted in the load chart.
  • Outriggers are to be fully extended and set at all times when practical.
  • Never allow the operator to “lift by the seat of their pants” if they can start to feel the crane tipping, then it is already too late, the crane has been overloaded.

We’d love to hear your comments and hear how this series has helped you. Feel free to let us know your thoughts using comment function below. Until then, have a safe day!

 

(Article originally published November 24, 2015, updated 2018)

 

6 Responses to “Part 6: Mobile Crane Stability – Don’t Be A Statistic”

  1. Nikos Mavris says:

    Great series of articles. Understanding the basics!

  2. Michael kloscak says:

    When running a front mount hiab 377 articulating boom crane should I run it over the cab with tire chulks in the front I feel running it off the back would waste 30 more feet I could get

    • Crane Tech says:

      Michael – Thank you for your comment. We are unable to respond to specific questions in this post as there are many variables that must be considered. We recommend that you follow manufacturer instructions, range diagrams and load charts and set up safely according to all the conditions at your site.

  3. autolinkpk says:

    Thank you for sharing your useful information. It is very attractive and effective post. I hope you will post again soon.
    mobile crane supplier in Pakistan

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