Some of the tallest buildings in the world, like the Petronas Towers, are supported by thousands of steel-reinforced concrete columns and beams. Steel is very strong in tension, and concrete is strong in compression, so together, they can be pushed and pulled without breaking or collapsing -- ideal qualities for a tall apartment building in a windy city. But most importantly, concrete is a good insulating material. It protects the steel for a long time from melting in a fire. Good job!