Iron isn't melted to make a horseshoe. It's heated, then hammered on an anvil and bent to its shape. If heated too much, or whacked too hard, it tears.
The Trade Towers were nothing but a large forge, where the steel was softened by jet fuel, etc., and then bent to the point of breakage from so much weight above acting as a massive hammer.
Basic blacksmithing must be too difficult for all those intelligent truther moonbats to understand.