load combinations cranes, live load snow

huangyhg

load combinations? cranes, live load & snow?
i am adding hoist beams and cranes to the underside of a roof in an existing building, and am not sure about the loading combinations.  i am using the national building code of canada where live load is described as min loads, snow and cranes including impact.  i don't think it is reasonable to use full live, snow and crane loads all at the same time.  is there a clause that allows me to reduce one or the other?
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in spain steel code nbe ea-95 yes, when 3 ll are combined all dl and ll go multiplied by 1.33 whereas for 2 ll plus dl at least one of the ll take 1.5 (and two ll take 1.5 for some combinations).
with eq the strength design becomes probabilistic or service level with ll feduced even further.
international building code ibc-2000 (usa): crane hook loads need not be combined with roof live load or with more than three-forths of the snow load or one-half of the wind load (section 1605.3)
same provision was in uniform building code ubc-97