Oh my god. I didn't see this before my last post...

The steel box-beams (that I think you are seeing and mistaking for the entire core structure) are just an element of the core structure. They rose up on the outside of, or were integrated into, the core-walls. I would need to check, but I would expect that these boxes were also filled with re-bar and concrete as the pouring progressed upwards. The box-beams are NOT the beginning and end of the core structure, there is an awful lot more to it than that. It is a reinforced concrete structure - even probably inside the boxes that have caused you so much confusion.

Royston, have you looked at any of the pictures, videos, or blueprints I've provided here in this thread? I don't know how you could possibly have seen them and still be pursuing this line of idiocy. There may have been concrete involved long after the actual load bearing structure was built, but the concrete had nothing whatever to do with what gave the core it's structural integrity. In the pictures and the videos, there is no concrete involved whatever while the structure is being built from the ground up. It may have been added later, but it was not integral to the structure of the cores.

If you keep hammering on about concrete without having seen the pictures, videos, and blueprints, you really are embarrassing yourself in ways you can't even imagine right now, because everyone else who has looked at them can see what a fool you're making of yourself.