Statics problem

[illini8181]

Basic statics question: If I have an object hanging cantilevered from an I-beam, how do I find the bending stress part way up the I-beam (see attached sketch)? I know that my basic equation will be sigma = Mc/I. The moment at the lower end of the beam, M’ = W*L, but I cannot just move this moment to the location I am trying to take my section cut, right? Using what I remember from shear and moment diagrams, is the moment simply W*L at the one end of the beam and then zero at the other, and varies linearly in between? If that is the case, finding the moment acting on the section that I would like to analyze would be easy… but maybe I am missing something?

 

[desertfox]

Hi

If the beam was built in at one end and cantilevered out the bending moment would be constant along its length and equal to W x L, however in your sketch its on crane slings so the whole beam will try to rotate from right to left creating tension in the slings.

 

[dhengr]

In fact, tension in one sling, and likely slack in the other. Put some dimensions, sizes, loads, etc. on your sketch so we really have something to talk about, otherwise Dessertfox has pretty well answered your question. Why are you lifting a load with such a crazy arrangement?

 

[Engdoitbetter]

As desertfox put it, the beam will rotate so that the loads (sling tension and W) are aligned.

This does seem a bad situation for load lifting.

Regards,

Stefano

 

[chicopee]

No the crane hook and the centroid of the whole system(H pile weight ant the W) will line up with the crane hook. As it appears that the sling is a single leg with about half a wrap around the hook, it will slide on the hook, as the whole system rotates during lift, and assume equal tension on each side eventho. one side will be longer than the other side.

 

[chicopee]

Not only will you have bending stress at the connection between the H pile and the welded piece represented by W, you will also have shear and tensile stresses at the welded connection when the whole system is lifted and has rotated.

 

[rb1957]

as I see it the link will rotate so that the load and the reaction align (a simple two force member).

once you know the line of action of things, you can figure out the moment at the section required (how far is the section centroid displaced from the line of action).

Quando Omni Flunkus Moritati