$(5$pt$)$ Hollow circular post ABC supports a compressive load P$,=2100$ lb$.$ A second load Pz is uniformly applied to the cap plate at B$,$ and can be treated as a single concentrated load of magnitude P$2.$ The dimensions $($diameter and thickness$)$ of theparts of the post are: dAs $=1\mathrm{.}125$ in$,118=0\mathrm{.}375$ in$,$ dc$=2\mathrm{.}0$ in$,(=0\mathrm{.}5$ in$.$Calculate the normal stress aAB.