Moment induced in frame from Brakes/Gearbox

[NE12345]

This is for a trolley frame on an overhead crane. I am being asked to provide calculations showing a frame is capable of withstanding the resisting moment due to equipment such as gearboxes and brakes. I am having trouble figuring out how obtain the forces / moments to apply to the frame. Does anyone know of a good resource that explains?

 

[tristan861]

I think Steel Design Guide 07 would help

 

[dhengr]

NE12345:
Dig out your Engineering Mechanics, Strength of Materials and Machine Design textbooks and do some self-study. Break the problem down into a simple step-by-step process, free body diags., etc., simple sketches at first, as you work through the problem and try to understand it. This sometimes takes several passes. I would assume you have the engineering drawings for this system and its major components, or you are trying to develop the same. Look at the brake system kinda as a closed box for starters; the brake application imparts a torque which would cause the whole box to spin, except for the fact that it is restrained by your structural frame. Those reactions are your frame loads. The same for the gear box, an input torque and an output torque must be restrained by your frame, and you know where the bolt holes are for this. What goes on inside these boxes is reacted within and by the box itself and brake design, etc. The same goes for the lifting cable drum, and the motors which power each unit. Then, all of these units are coupled together in some way.

These kinds of problems are actually more interesting and fun, if you are so inclined, than more of the same old simple beams and columns involved in run-of-the-mill building design. Your frame must support the various mech. equip. at their bearing feet and bolt holes. This locates, and ultimately sizes, many of your framing members. Of course, you have to support the weights of the equip. and give due consideration to impacts, inertial loads, vibrations and the like. And, your frame should be cleanly designed and detailed, allow for access for maintenance, and at the same time be easy to fabricate, weld and install. Good clean details and welding are essential for a good design.

 

[WARose]

I also recommend DG 7. I'd also have a look at the CMAA [Crane Manufacturer's Association of America] design manual as well. They get real specific on a lot of the forces that get boiled down in DG 7.

 

[NE12345]

Going back through references suggested I came up with the attached method. For the method the force in the pads / bolts uses the full moment of inertia which when I perform a check of the forces around the axis the resultant moment does not equal the initial moment. This is due to the local moment of inertia in the equation I + Ad2. Should the moment of inertia only be the Ad2 portion?