In a number of designs, a beam will have an underslung welded plate attached, as shown below:
In this sketch, a symmetrical standard steel beam/column of dimensions H1 x B1, with web and flange thickness w and t, has a wider plate welded under it of dimensions H2 x B2 (with B2 >> H2, ratio around 10:1 ~ 30:1).
For simplicity, I'm only considering stiffness in the vertical plane, not torsion/eccentric/lateral loads.
An example might be, if symmetrical static vertical point loads/UDLs were applied on the plate of such a beam, at both sides, at various points along the beam's length, and one wanted to evaluate the beam's bending moments or deflection along its length, or something like that. The usual methods for loads on a simple beam would be used, but you'd need to know its area moment of inertia first.
I'm assuming one doesn't just add the area M.o.I. (or 2nd moment of inertia - same thing) of the two together, as the value of the composite depends on the positions of the two.
What's the easiest way to calculate the value for this setup?