Building blocks
Tarp Fence Corner Blue
While not as sturdy as solid concrete, iron constructions have high structural integrity, requiring fewer support pillars.
Harvest drops
Iron× 10
Taken apart with a harvesting tool (axe, pickaxe, shovel), before perks and tool bonuses.
When it collapses
Falling, it leaves 
Scrap Metal Pile (60% of the time) where it lands.
Where to find (9 POIs)
Doominium Tower (tier 4), Shady Woods Amphitheatre (tier 3), The "Broken Dreams" house (tier 2), Oskar's Dumpster (tier 1), The Roland Residence (tier 1), The Smokehouse (tier 1), Downtown Construction Site, Industrial Construction Site #12, Junkin.
Points of interest built with this block (any of its variants), the highest tiers first, from the game's prefab files.