CMAA 74-15 Load Combinations for Projecting Beam Under Running Bridge Crane Movement

[steel_possum]

I'm using CMAA 74-15 to design a single girder under running projecting beam bridge crane structure. It is completely enclosed by a larger existing structure, so no wind loads. Does anyone have any advice on how to separate out the vertical, lateral, and longitudinal forces from the given Load Combinations from CMAA 74-15 Section 3.3.2.5? I think I'm pretty close to doing it correctly, but the part that is particularly confusing is this: notice how there are DLF factors for the bridge and the trolley, because the bridge and the trolley may have different speeds. So, should the movement of the bridge and the trolley be included simultaneously in the same linear combination as shown in (for example) Case 1 (Section 3.3.2.5.1), or should they be considered in two separate Case 1 linear combinations? (Keep in mind that what is perhaps a lateral Case 1 combination of forces for the bridge moving, would actually sum not with lateral trolley movement, but with longitudinal trolley Case 1 movement.)

This problem becomes a bit more confusing when the projecting beam, which rides between the bridge beam and the trolley, comes in to play. My current plan is just to add in another PBL(DLF_PB)term (PBL = Projecting Beam Load) into Case 1 (Section 3.3.2.5.1) for example, and call it a day. I guess my other option is to go through all the cases for each possible combination of a thing moving on another thing separately. All this I guess is contingent on only one movement occurring at a time on the crane.

Any tips or ideas for how to account for these loads in combination (and interpretation of CMAA) is appreciated!

 

[SJBombero]

DLF and HLF are "Vertical Inertial Forces" applied to the respective loads which are moving. I think Case 1 is clear that the effects from the trolley and bridge multiplied by their respective inertial factors are additive. If I am understanding what the projecting beam is correctly, it would be considered under "associated equipment" mentioned in the DLF definition. If it moves with the trolley, then it's DLF would be the same as that of the trolley.

 

[steel_possum]

SJBombero, thanks for the tip.