I seem to recall that the ATPL theory notes described severe turbulence as creating "a risk of structural damage".
I've had 2 experiences of what I'd call strong turbulence. First just south of Dewsbury inbound to Leeds which involved repeatedly having my head smacked on the roof and not being able to focus on the instruments, and the second departing the US when cabin crew ordered everyone to pour their hot drinks on the carpet before they and their trollies (and a couple of halfwits who thought they were too important to weat seatbelts) got slapped between roof and floor a few times with some minor bone breakage.