Preparing to design concrete beams/slab for crane tie-ins

[xp1]

Hi all, I'm having some difficulty figuring out the load path taken by the forces from crane to strut to embed connection. I've attached several drawings to present the situation, it's pretty typical I believe. The crane has 3 struts tying into 2 "shoes" made of several plates welded together.

One thing I'm wondering about is, does the height of the "crane box" - or where the struts attach the the crane - does it's height above the slab matter? I was told that this 2'-10" will cause a greater moment than if it were level with the shoes, but I'm having trouble understanding why. They've given us forces in the struts, which are the entirety of forces that will be transferred to the shoe; why does it matter where the box is? I'm thinking this only affects the horizontal and vertical components of forces. To me, it's significant that where they enter the shoe is some distance above the slab so there will be a small moment there, but that's all I see.

The next thing is, I was planning on using these strut forces and finding the horizontal and vertical components. The vertical would be point loads, while the horizontal I would turn into a moment with the distance being top of slab to strut connection. Does this make sense? And then I would analyze the slab with a point load and point moment.

Thanks for any guidance, suggestions, or other input.

Structural Engineering Intern

 

[dhengr]

Xp1:
There was at least one other thread on this same topic a year or two ago. Search in the Structural Engineering forum, this forum #507, I remember participating in it. Yes, your sketches/attachments are pretty typical of those crane conditions. Your general approach seems right to me. You should resolve the strut loads into x, y & z load components at the pins on the two shoes, and then resolve these into the slabs. Sometimes easier said than done. In some cases you may wish you had some shear lugs welded to the underside of the shoes. The crane company supplies the shoes or do you? In either case you may want to check the shoe stresses under your load set. Obviously, you gotta miss the slab rebar, and the bolting may be through bolts.

 

[Lomarandil]

Note that the strut forces enter the shoe both vertically and horizontally offset from the center of your bolt group. In this case, they should offset each other w.r.t. moment, but that may be the root of the concern from someone giving it a first glance.

Another thing to consider is that the strut or shoes may only be rated for operation within a certain angle from horizontal -- I've come across that before.