Barracks
The barracks radical and the barracks kanji are the same!
Know your radicals, yo!
とん
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Barracks are pretty big, so they weigh a ton (とん). And they probably take tons of materials to build.
Imagine trying to lift some barracks. They weigh a ton! How are you supposed to do this? Why would you even try to lift something that obviously weighs a couple tons?!