For the frame shown below:

$($a$)$ Draw all possible failure mechanisms showing the exact position of the plastic hinges at the

beam$/$column connections

$[14$ marks$]$

$($b$)$ Find the loading factors $$ corresponding to the collapse loads of all mechanisms you

have identified in $($a$).$

$[10$ marks$]$

$($c$)$ Which of the collapse mechanisms you have found in a$)$ is the "true" one? Why?