Design of Overhead crane hoist

[johnthebest]

the contractor of our project has stated the following:

As Good engineering Practice minimum capacity of the permanent lifting facilities (Overhead crane, Hoist) shall be maximum maintenance weight of the Equipment to be lifted plus 10% margin .

is 10% margin enough to take into the calculations? is there any international code that specifiy the margin?

 

[Ron247]

I am not clear on what you are asking. Is he talking about choosing a size of crane to purchase? Choosing a crane capacity is a little more involved than that. Lifted load, weight of rigging, weight of any spreader beams etc are all to be included in the crane capacity. 10% overage is not a requirement. It may be a minimum, but overage generally reflects "uncertainty". The more uncertain you are about loads, the higher the percentage.

 

[spieng89]

If you are referring to what load to design for; IBC chapter 4 states account for additional 25% live load of the crane capacity e.g. 2 ton crane, design for 2.5 ton.

 

[johnthebest]

Thx for ur replies. The crane will be designed based on the maximum load to be lifted (will be defined later). The contractor added a margin of 10% in his design philosophy. The question about the margin. Is there any references that specify the margin? And if I should accept 10% as they proposed.

 

[CANPRO]

Perhaps when he says design load, what he means is the capacity of the crane. For example, if your max anticipated load is 9 tons, design for a 10 ton crane. From there you design the crane and supports for 10 tons according to the governing standards and good engineering practice.

 

[Ron247]

Based on your ID showing you are a mechanical, I assume you are asking about sizing the crane. For that, I would assume 10% is ok for an estimate of needed size. If you are talking about designing a crane building, then the 25% overage noted by spieng89 is an added amount to reflect impact to the structure itself caused by the crane usage. Two different animals.

 

[johnthebest]

@ Ron274. Thx for ur reply. Exactly I am asking about sizing the crane. Based on what 10% is accepted. Is there any reference or an international code that support this assumption?

 

[dauwerda]

johnthebest, I don't believe you will find anything in codes telling you how to size your crane. What the contractor proposes seems to be fairly straight forward. Provide a crane with enough capacity to lift the heaviest piece of equipment expected with 10% added to allow for rigging and some fudge factor. The code(s) doesn't care if your crane is capable of lifting the heaviest piece of equipment in the facility (the client does). I have seen clients install smaller cranes for typical maintenance knowing that if major maintenance/replacement would be needed they would have to remove roof panels and use a large mobile crane. I have also seen them do the exact opposite, similar to what your contractor is proposing.

 

[BMart006]

Depending on the crane type there are a few different design codes you can use. For typical bridge cranes, CMAA 70 (double girder) and CMAA 74 (single girder) exist. Both of these have dead load (minimum 10%) and live load (minimum 15%) factors as a part of the design. Monorails can be designed to ANSI/MHI MH27.1 which also has a live load factor. These factors are partially due to the acceleration forces related to initial hoisting and braking actions. The requested 10% may be related to those or may be saying design the crane/hoist so that the rated capacity is 10% higher than the highest static load to be applied to the hook. Either way, it is wise to look into the ASME B30 codes (B30.2, B30.17) and OSHA to determine if there are any additional criteria you should consider (e.g. testing to 125% of rated capacity for certification).

 

[FLCraneBuilder]

If you are asking what the "Rated Capacity" of the Crane, runway system & facility should be...
THE OWNER typically makes that decision
If you are the facility design contractor - then the 10% adder for "rated capacity" makes sense
If you are the general contractor (building the facility) - you do what the owner and/or A&E tell you to do
If you are asking about additional design criteria such as impact, deflection limits, load test effects, etc, then you use the codes.
AISC, CMAA, MHI, ASCE, IBC, AISE etc