$5$b$)$ In structural design it is required that a variety of load combinations are used. One such combination is as follows:

Design Load$=1\mathrm{.}2D+1\mathrm{.}6L+0\mathrm{.}5S$ where $D$ is dead load, $L$ is live load, and $S$ is snow load.

For which of the following condition$($s$)$ would this equation not be applicable? Explain your answers.

i$)$ A structure loaded such that one or elements have yielded inelastically

ii$)$ A structure that uses nonlinear elastic materials

iii$)$ A structure for which materials remain linear elastic