The $400 million mistake
The initial problem discovered at Harmon Tower
was rebar that was misplaced within 15 floors
of the building, weakening the entire structure.
A large slab of concrete won't support even its
own weight on its own so concrete is included
in the middle of the structure to hold the
concrete together. But if it's placed too high or
two low in a floor it won't hold together and it
will weaken the whole structure.
After the problem was discovered, the plan was
to cut the building's height from 47 stories to
28, but testing by structural engineering firm
Chukwuma Ekwueme discovered over 7,000
defects. By the time testing was completed,
which included pulling out samples, the building
wasn't even salvageable.

http://www.fool.com/investing/general/2014/11/22/las-vegas-mega-flop-why-this-400-million-hotel-is.aspx