Rigging Beam 3

[TennStructural]

I am unclear on the impact factor used for a trolley beam or hoist beam design. In the past, I have used 25% impact for design, since everything below the hook will be proof tested for 125% capacity, however, if everything below the hook is tested elsewhere, does the hoist beam itself have to be designed for 125% of its marked capacity?

Thanks

 

[JAE]

We use ASME BTH-1 for beams like this (for USA projects). In fact - all our contractor friends do the same.

https://www.asme.org/products/codes-standards/design-of-below-the-hook-lifting-devices

This outlines structural design of spreader beams, etc. along with required safety factors.

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[rb1957]

that sounds really low to me ... impact factors are typically 2.

and wouldn't the beam be designed for a much higher safety factor ? (3? 4??, from Health and Safety codes ??)

another day in paradise, or is paradise one day closer ?

 

[TehMightyEngineer]

TennStructural: If you're in the US then OSHA requires that all new or modified cranes (which includes monorails and trolley beams) be load tested to no more than 125% of their rated capacity.

https://www.osha.gov/pls/oshaweb/owadisp.show_document?p_table=INTERPRETATIONS&p_id=27287

You might also want to get a copy of ASME B30.2 or CMAA Specification 74 depending on what you're looking at designing. I would actually not use ASME BTH-1 for a trolley beam as that is intended for "below the hook" (BTH) items such as lifting beams. Trolleys and monorails I would typically design to ASCE 7 (see section 4.9) and AISC 360 (the steel book) with some consideration of ASME B30.2 or CMAA Specification 74 as applicable. Some additional consideration should be given to load location (below the flange) and torsion in the beam from side loading or swinging loads, trolley beam bracing (especially in cantilevered monorails), and bottom flange bending under trolley wheel loads (this often controls for monorails but is mostly a serviceability concern).

rb1957: This is a common misconception that leads people to overload cranes and lifting beams that are (correctly) not designed to really large factors of safety. Most bridge cranes, monorails, spreader beams, and such are designed for a safety factor of 1.6 to 2 (for flexure, sometimes higher per ASME BTH-1) and generally impact isn't even considered in the case of hand-geared trolleys or relatively benign lifting conditions. The items that are rated higher includes lifting hardware; hoists, chains, wire rope. These are all rated for a much higher safety factor.

Maine EIT, Civil/Structural.

 

[TennStructural]

Thanks for the quick responses. I have a pretty good grasp on BTH component design and testing. I was mainly wondering if OSHA has specific design criteria for Above the hook rigging hardware. I understand that there is some factor of safety in ordinary steel design, given by ASD or LRFD design methods.

If the BTH components are going to be proof tested on the hoist beam, I would design the beam for the test load. Since the BTH components are already qualified, can I design the above the hook beam for 100% of the rated capacity, in accordance with standard ASD or LRFD methods? Does OSHA have a specific impact factor to use for the hoist beam (not spreader beam)?

 

[TennStructural]

TehMightyEngineer,

I just checked out your link. That was what I was looking for! I needed some justification for designing my beams for 125% of the rated capacity. I knew I had seen it somewhere on OSHA site, but that has been a while. I started working for a different company, and I have to justify it again. I am printing a copy now for all to see.

 

[steele6707]

ASME NUM-1-2009 is titled "Rules for Construction of Cranes, Monorails, and Hoists (With Bridge or Trolley or Hoist of the Underslung Type). I have a few pages of the 2000 edition that has the local flange bending due to wheel loads example. I believe this replaces the old CMAA 74 document. I suppose this is the "above the hook" document.

 

[TehMightyEngineer]

Good to know steele, I'll have to see about getting that in our office as we do a lot of lifting beam and monorail designs.

Maine EIT, Civil/Structural.

 

[IFRs]

Some states have different testing requirements, Michigan comes to mind