Overhead Crane - OSHA 125% Loading

[Wildcat17]

Do you design crane runway beams to accommodate the 125% OSHA test loading for overhead cranes or do you allow the test load to rely on the safety factor?

I am having a difficult time understanding why a 20 ton crane would need to be designed for 25 tons.

I have not seen any crane design references (including AISC Steel Design Guide Series 7) that address the 125% test loading requirement.

Any documented information that indicates the crane support structure shall be designed for 125% of the rated crane load would be appreciated. Thanks!

 

[chrislaope]

I guess you are talking about following:
ASCE7-10 Crane load 4.9.3: vertical impact load, maximum wheel load for 2 type cranes need increase 25%. (page 16)

 

[TehMightyEngineer]

I believe the OP is talking about the OSHA requirement that you test the crane/lifting hardware to 125% of the rated capacity.

To answer your question I do not design for this. My reasoning is the intent is to test the crane by purposefully going into the safety factor a little bit during a safe/controlled test load. By increasing the design strength you aren't going into that safety factor and there may be a fault that goes undetected during the test.

Short answer, don't design for the 125% test load. But, as chrislaope said, design it for the impact factors as appropriate.

You'll also want to look at the gantry crane design specification; CMAA Specification 70. There are additional rules for deflection, straightness, and so on for runway beams of gantry cranes.

Maine Professional and Structural Engineer
American Concrete Industries

http://www.americanconcrete.com

 

[SlideRuleEra]

Wildcat17 - The crane runway beams and other support steel will easily support the 125% OSHA test load, without having to do anything extra. The supporting steel will have to be designed for a 20 ton load anywhere along the bridge crane's usable length. As I understand the OSHA requirement:

1910.179(k)(2) Rated load test. Test loads shall not be more than 125 percent of the rated load unless otherwise recommended by the manufacturer.

The location of the 125% test load is not specified. Apply the 125% test load at midspan and the reactions at both ends are still very reasonable when compared to normal operating requirements. See this sketch:

http://www.SlideRuleEra.net

http://www.VacuumTubeEra.net

 

[TehMightyEngineer]

Also note that the test load doesn't have to go any higher than an inch or two off the ground. You simply need to stress the lifting hardware to 125%, hold it for a bit, then let it back down and check for any signs of failure.

Maine Professional and Structural Engineer
American Concrete Industries

http://www.americanconcrete.com

 

[TXStructural]

The OSHA requirement is an "actual load" test. Such a proof load test is to establish that the equipment will function safely at rated load. Your design stays elastic through a minimum of 160% rated load and would be acceptable. (Using a 1.6 or 1.7 live load factor in design.) There would be no need to design for the 125% test load, unless there is concern for a suddenly-applied load or deflection. The OSHA load test for general industry is:

1910.179(k)(2)
Rated load test. Test loads shall not be more than 125 percent of the rated load unless otherwise recommended by the manufacturer. The test reports shall be placed on file where readily available to appointed personnel.

This load test is for the hoisting equipment and can be conducted anywhere along the support system, so you could specify where along the rail/runway the test should be conducted.