$9\mathrm{.}11$ As shown, a curtain wall is constructed of brick masonry $(=0\mathrm{.}000005i\frac{n}{i}n-F).$ The bottom of the masonry wall bears on the leg of a steel angle that is welded to and extends from a steel spandrel beam at each floor. The wall extends to the bottom side of the leg of a steel angle on the upper floor. The wall measures $12\mathrm{.}0$ ft and is fully restrained between the angles. It is installed at a temperature of $55F.$ On a hot summer day, the temperature of the wall can rise to $90F.$ In the winter, the temperature of the wall can fall to $20.$ Stress due to weight of the wall is $15l\frac{b}{i}{n}^2$ at the base of the wall $($at the bearing point on the angle$).$

$($a$)$ Determine the maximum thermal stress that develops in the curtain wall.

$($b$)$ Determine the maximum stress that develops in the curtain wall with this temperature change.