Load Carrying Capacity of Beams in 3-Story Building

[checkmatechamp]

If you have say, a 3 story building and each floor has I beams (with cross pieces) carrying the weight, would the beam holding up the second floor have to carry the load of the third floor as well? I don't think so (if I drew my FBD correctly, the largest reaction should be the one pushed up by the soil and the foundation). Can anybody clarify this?

 

[billy_joule]

It depend entirely on your drawing - it's possible to draw it either way.

Take a look at a building frame next time you see a construction site (or use google image) - Which way have they done it? Can you think of why it's done this way?

 

[russ_watters]

It's probably better if it didn't, but yes it can be done either way. But dear lord, make sure it is done right either way:
https://en.wikipedia.org/wiki/Hyatt_Regency_walkway_collapse

 

[Shane Gribben]

Short answer no.
Long answer it depends on the designed for load path. If you have a standard arrangement of primary and secondary beams to columns then the force as a result of floor slabs should be carried by the beams to the columns, columns to the to the foundations. With only slight increases in stresses at the connections between beams and columns due to the floors above, as a result most building codes suggest designing beams to withstand the shear force bending moments and torsional forces caused by the floor during service. And the main focus is on connections to ensure the load is transferred through the structure to the foundations.
If you have a non standard arrangement, such as in Hyatt Regency, with floors above supporting floors below via the use if tie rods and suspension cables, I suggest you look at bridge engineering, and talk to a structural/ bridge engineer.

I might come back to this to elaborate with pictures etc...