The Rigida Andra 30 CSS have a wear gauge built into their section. When they are worn they will develop a warning split like this:
Not so for the Grizzly
.
The good thing about this is that, despite the shock value of it, the rim is still essentially sound to continue riding for a while, due to the position of the thin wear gauge area.
With regular rims (and I'd assume the Grizzly too) the first signs are a concave brake surface. This will continue OK for some time, then the rim will develop a brake pulse effect - this is not a buckle but a bulge in the rim sidewalls each side. This is the warning to scrap the rim - soon after you may have a split (more severe grabbing) or worst case, a sidewall blow-out