How do you calculate the stopping distance of a bridge crane?

How do you calculate the stopping distance of a bridge crane?

CRANE Power Mast Abraham writes:

“How do you calculate the stopping distance of a bridge crane to see if you meet the OSHA standards? I need help determining if our bridge cranes are traveling too far after we release the travel button on the remote control.“

Tom answers:

Both OSHA 1910.179 and ASME B30 publish standards which address bridge and trolley brakes with regard to stopping distance.  Below are some OSHA and ASME guidelines:

  • OSHA 1910.179 (f)(4)(vii)  Brakes for stopping the motion of the trolley or bridge shall be sufficient size to stop the trolley or bridge within a distance in feet equal to 10 % of full load speed in feet per minute when traveling at full speed with full load.
  • ASME B30.2-1.12.3 (a)(1) brakes should have torque capability to stop trolley/bridge travel within a distance in feet equal to 10% of rated load speed when traveling with a rated load.

OSHA and ASME specify “rated load speed.”  This speed is set by the crane manufacturer and can be found in the specifications section of the manuals supplied with the crane.  If not specified, you may use one of the following procedures:

  • One option is to determine 10% of the distance in feet. Put a full load on your crane and traverse the bridge or trolley at full speed for one minute. Mark the distance.  Most trolleys will run out of room long before one minute passes.  Take 10 percent (10%) of that distance. This would be the maximum “drift” distance allowed after putting the controls in the off or neutral position with the crane traveling at full speed with a full load. This approach is what many people try to do. It can be tedious. 
  • A better option might be to determine 10% of a minute. The standard states “10% of full load speed in feet per minute.“  6 seconds is 10% of a minute.  When traveling at full speed with a full load the bridge or trolley should stop within 6 seconds after going to the neutral or off position.  With less than a rated load, the bridge or trolley will drift shorter distances/less than 6 seconds.
Tom Reardon
Tom Reardon is a Technical Instructor specializing in Hoists & Overhead Cranes for Columbus McKinnon Corporation.
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10 Replies to “How do you calculate the stopping distance of a bridge crane?”

  1. I have a brand new Crane That Colin Crane put up. The crane drift and all XYZ movements. With no control from the operator to be able to stop the crane other than the East op which we would know what would that would do if you hit the e stop with a load. Can the crane be adjusted to Old School settings

  2. A good rule of thumb is to stop the crane with full load at full speed as quickly as possible without swinging the load.
    An old rule of thumb was to stop within the distance if it’s own end carriages

  3. Hello Dave,

    ASME B30.17 – When traveling with rated load, it must stop travel equal to 10% of the rated load speed. Our 6 second rule is a valid method to quickly and conveniently check for compliance with the stopping distance requirement. It is not precise, but it is also not difficult, and it should be conservative in the conclusion. Any crane carrying rated load and moving at full traverse speed which does not come to a complete stop in 6 seconds is certainly not in compliance and would require a full and thorough evaluation. There are special cranes with unique features and unique applications which utilize sophisticated deceleration methods. These cranes and applications do not fall within the scope of this article and should be evaluated based on the crane manufacturer’s or crane owner’s recommendations.

    Your best bet would be to write ASME B30.17 and ask for a letter of interpretation with regards to cranes with special features.

    Tom

  4. Gentlemen,

    The way I read the standard B30.17 is that the Crane is to be EQUIPPED with Brakes capable of stopping the Crane in a specified distance with a full load at Rated Speed. This seems to tell me that a crane must have these capabilities, not necessarily that the brakes be adjusted to provide these forces. This seems to me to be a design requirement rather than a performance adjustment requirement. There are more and more applications that employ anti-sway apparatus that do not stop the travel within 10% of the distance that would be covered in 6 seconds (at any speed) as described above. Doesn’t the standard simply say that a crane cannot be delivered to an end user if it cannot be adjusted to provide the specified performance if desired? Thanks in advance, Dave Ross

  5. Hello Rathore,
    Standards apply for specific regions. There is nothing in the EN14492 hoist standard for Europe that specifies a minimum stopping distance. The ASME B30.16 hoist standard for North America only states that the brake must stop and hold rated load. It does not suggest any requirement for stopping distance or time.

    Since your company is located in India, you would need to determine the local standards to determine whether or not your requirements are acceptable.

    Peter

  6. Please tell as the formula or allowable travel in lowering motion when thruster brake is applied.
    My hoisting speed is 4.5 M/min and when brake is applied in lower motion it travel 45 mm,is it acceptable as per international standard.

  7. Once again, this is a conservative method for a crane service technician to make an initial evaluation of the braking characteristics of a crane. This applies to typical cranes in general industry, utilizing electrically released, mechanically set, disc or shoe and drum type brakes.

    There are special purpose cranes and unique applications which utilize sophisticated deceleration methods. These cranes and applications do not fall within the scope of this article and should be evaluated based on the crane manufacturer’s or crane owner’s recommendations.

  8. In your 6 second example, I agree you are conservative (by a factor of 2 in the case of a constant deceleration) and well inside of the standard. If you have a long and slow deceleration it can take longer than 6 seconds to stop but you can still easily be inside the braking distance requirements in B30 and 1910.179. Your last sentence that “Any crane carrying rated load and moving at full traverse speed which does not come to a complete stop in 6 seconds is certainly not in compliance..” is incorrect.

    If I have a very large crane operating at its capacity moving the Space Shuttle and it is moving at 20 feet/minute; it has to stop in 2 feet. From it’s maximum speed using a constant deceleration and stopping in 2 feet, the deceleration to a stop will take 12 seconds. Of course it can stop in a shorter distance, but in order to see if one is in compliance an overly conservative approach is not the most accurate answer.

  9. We agree that 6 seconds is not the same as 12 feet. The 6 second rule is conservative and is used by service technicians who seldom have access to a crane’s “rated load speed” information when evaluating the stopping distance of a crane or trolley.

    Our 6 second rule is a valid method to quickly and conveniently check for compliance with the stopping distance requirement. It is not precise, but it is also not difficult, and it should be conservative in the conclusion. Any crane carrying rated load and moving at full traverse speed which does not come to a complete stop in 6 seconds is certainly not in compliance and would require a full and thorough evaluation.

    Thank you for the opportunity to address this matter in greater detail!

  10. Sorry but 6 seconds stopping time is not the same thing as 10% of the speed (distance in feet).

    If the crane moves rated full speed of 2 feet/second that would be 120 feet/minute so 10% would be 12 feet. You would need to measure from when the brake is applied until it comes to a stop and not exceed 12 feet.

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