The two halves of the rim have an interlocking lip of approximately 1/8" when they're new, and if that lip gets damaged by rust or mishandling during assembly the already minimal latching area can be compromised to the point of separation. The halves of the rim are assembled by tilting one part of the rim at an angle and driving it over the other piece with a heavy hammer. The barrel section of the wheel distorts enough from the angle to let the pieces slide over each other, then they align and lock as the tire is inflated and the beads seat.

There is one narrow notch in one part of the wheel to allow a specially-shaped pry bar to be inserted to take the rim apart once the air pressure is released and the beads are driven away from the rim flanges.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!