To crack up has several different meanings:-
From the Free Dictionary:-
1. To praise highly: He was simply not the genius he was cracked up to be.
2.
a. To damage or wreck (a vehicle or vessel): crack up a plane; crack up a boat.
b. To wreck a vehicle in an accident: cracked up on the motorway.
3. To have a mental or physical breakdown: crack up from overwork.
4. To experience or cause to experience a great deal of amusement: really cracked up when I heard that joke.
In this photo it's the walls of this building that are cracking up, and it's no joke.
