In a 4 story building, I have a beam in the third level, which I have modeled as a stub cantilever with a back span, since I wanted two different beam sizes .I have modeled them as lateral to modify the fixities. I have defined the fixities as shown for the beams. For the Column, both top and bottom are fixed. RAM steel beam gives me a design for both the back span and the stub cantilever. (Back span is treated as simply supported I suppose). The steel post processor in RAM frame shows that the back span member is failing with a S.R. = 3.5. Could anyone please suggest what should the fixities for the beam and the column be?
If you are going to have a fixed connection on the right end of the back-span beam, you might as well use a traditional beam with cantilever, but a stub is also acceptable. The problem with the back-span is probably that the unbraced length is too long for the bottom flange (negative bending).