Lifting Loads - Proper Way to Account for in Design
Lifting Loads - Proper Way to Account for in Design
(OP)
I have been asked to design a steel frame to facilitate lifting a piece of equipment (approx 5,000 lbs.) to the rooftop of a building. The frame will be fabricated around the equipment, then the cranes will be rigged to the frame. Direct rigging of the equipment isn't practical. Frame will likely be W6x25.
What is the proper way to account for the effect of lifting on the frame members? It seems to be it would be like an impact load. I have seen references to adding 25% (or 10%) to the static loads. Are there commonly accepted (and valid) approaches?
Thanks in advance.
What is the proper way to account for the effect of lifting on the frame members? It seems to be it would be like an impact load. I have seen references to adding 25% (or 10%) to the static loads. Are there commonly accepted (and valid) approaches?
Thanks in advance.






RE: Lifting Loads - Proper Way to Account for in Design
RE: Lifting Loads - Proper Way to Account for in Design
You might check out ASME B30-20 which is applicable to spreader bars and similar below-the-hook devices. (I think it specifies FS of 3, based on yielding.)
RE: Lifting Loads - Proper Way to Account for in Design
RE: Lifting Loads - Proper Way to Account for in Design
RE: Lifting Loads - Proper Way to Account for in Design
I also include a 60%/40% distribution factor between slings unless the load path is very clearly determined and a 75%/25% when the lift is done with more than one crane hook.
Dead load factor between 1.1 to 1.4 deppending on how well calculated it is and do not forget to include the weight of the rigging. Sometimes it is significative.
It might appear very conservative to some, but I have seen a couple of crane operations gone South and it is not pretty when it happens.
RE: Lifting Loads - Proper Way to Account for in Design
You also need to consider how many points of lifting are going to be used. Usually, 4 lifting points for typical equipment's protection frame. Bear in mind, when you design the padeyes, you also need to consider the condition where at the loads are not equally distributed. ( let say 2 lifting points carry 75% of the 1.25 x weight).
RE: Lifting Loads - Proper Way to Account for in Design
RE: Lifting Loads - Proper Way to Account for in Design
ZCP
www.phoenix-engineer.com
RE: Lifting Loads - Proper Way to Account for in Design
ASME B30.20-2003 20-1.2.2
"The load-bearing structure components of a lifter shall be designed to withstand the stresses imposed by its rated load plus the weight of the lifter, with a minimum design factor of three, based on yield strength of the material, and the stress ranges that do not exceed the values given in ANSI/AWS D14.1 for the applicable condition. ...."
In the US the following may help guide guide you:
ASME B30.20a-2001 Structual and Mechanical Lifting devices. Section 20-1.2.2 Construction
CMAA crane requirements
AASHO 1.6.17
Steel Construction Manual-AISC
Occupational Safety and Health Administration (OSHA) 29 CFR standard 1926.753(e)(2) and 1926.251
American Society of Testing and Materials Specifications A391
Naval Facility Command NAVFAC-307
American National Standards Institute, "Below The Hook Lifting Devices"
RE: Lifting Loads - Proper Way to Account for in Design
The best information for design of the lifting frame is an article entitled
"Design and Construction of Lifting Beams",
by David T. Ricker, published in the
AISC Engineering Journal, Fourth Quarter/1991.
RE: Lifting Loads - Proper Way to Account for in Design