Hello guys. I did not understand why the book authors multiplied 1.5 & 2 with the moment of inertia of the rectangular portion of the beam. First one is for L shaped and second one is for an I beam. It is an example from "Design of Concrete Structures 15th edition by Arthur Nilson, Dolan & Darwin". Can anyone explain why did they do this. I calculated moment of inertial for the first one using parallel axis theorem and I got around 12000 in^4.
they are using a rule of thumb estimate on the relative stiffness of the T/L sections compared to a rectangular section (bh^3/12), computing the actual moment of inertia as you did via parallel axis theorem will give a more accurate answer.
