Any reason why the office tower wouldn't be steel?
Better still, why not precast??
I was looking at a tower in Frankfurt last year being built with precast columns and beams as well floor slab for a 40 storey tower. The ceiling where high with with openings in the beams for all mechanical work including duct work.
Very few tall buildings are built with steel these days, as it is cheaper to do it in concrete. Some developer prefer steel towers for various reasons to the point they are supper thin ones. Very few large fabricators left in NA to handle 25,000 ton projects to the point there are joint partnership to fabricate the steel for one.
The original BA tower was being built with large beans and columns until it die in the late 80's. Canron, the fabricator of the steel for the tower had 10 floors fabricated and sitting in the yard when the hold was put on this project. This was on top of what was already on site. The steel ended up going to the scrap yard and Canron going out of business, considering it was the largest one in Canada.
The current BA tower only saw a fraction of the steel in it compare to a normal tower, as most of it was steel joist in place of beams supporting the floors. Steel Joist has replace beams and columns building since they are lighter, cheaper to make and offer better head room. Also, faster to erect.
There are very few steel mills left in NA that roll beams and columns these days with most material coming in from off shore at a cheaper price than here.