Brazilian military facility

It's almost certainly storage for explosives. Sometimes very volatile substances, white phosphorous or dynamite for example, are stored in above ground buildings that appear to be rather flimsy. This is intentional. Small amounts are stored in separated buildings so if any catch fire only a small amount will burn/explode. The buildings are flimsy so they blow apart easily and quickly release the energy of the explosion. Even in a bunker everything would burn so there is no need to bother trying to contain the blast. Also, bunkers are built to keep bombs out, not explosions in. It makes little sense to build an expensive bunker to house cheap explosives.

There are a few bunkers on the compound, probably for storing more valuable weapons such as missiles or precision guided bombs/artillery shells. The cheap stuff (dynamite, WP) is stored in the cheap buildings but separated for safety.