conservativejock saidAre you talking about the elevator shaft that protrudes beyond the top floor?
NJDewd saidWhat is the name of this Atlanta building and what address?
Currently the Mandarin Hotel. It is in the 3300 block of Peachtree Rd. It was foreclosed and popped back on the market. The bidding process was as interesting as the development phase, the former of which I was involved, the latter of which I entered the bidding but laughed at my own bid. ;-) The construction phase burned $165MM.
Somewhere in this old place in which I reside I still have the individual floor plates for the Mandarin. There are some incredibly unique surprises in those plates, as there is a condo with a 35 foot ceiling located at a transfer floor.
In the photo the tower is topped out. The top two floors are unit #56. There is also something else shown in that photo at the very top that is key to my original post as to what is odd about the structure.
Ok. Time to explain the rest of the story.
The rather considerable structural challenge is to build such a thin tower to 575 feet above street level with the distances seen between decks. WTC1 would sit on the site of this tower and cover more area than the entire tower and promenade. I have added below an interior photo of an unfinished penthouse at the top of the tower. The Mandarin, the tower you see here, has deck spans of around one and one-half times that of the WTC. This fact is what generated my buddy at McNamara and Salvia to pick up the phone and enquire as to whom the structural engineering team was composed of.
Look at the very top floor where the exterior cladding is in place. It is obvious that the height there in the center opening is considerable. This floor in fact is a transfer floor, a floor where column loads from above are redirected to column loads below because the concrete structural elements -- the load baring elements -- do not align all the way down the tower.
The first twenty floors are composed of a post-tensioned box through which the tower itself rises. What you correctly call the elevator shaft is actually a structural member as well as a shaft that runs over 600 feet to a massive post-tensioned matt at the very bottom. The tower is not pinned to stone as you might expect. The matt or raft floats in soil. It is an integral park of the promenade that covers the entire site from the exposed garden top down four levels. The central core -- the elevator shaft -- is part of an outrigger system composed of the shaft itself and multiple transfer beams down the tower. This section is composed of both ductal concrete, self-compacting concrete, and of course steel reinforcement consisting of both rebar and select formed pieces.
In the upper left hand corner of the photo by the way is a structural tie beam. There is no post tensioning in the deck. This allows the deck to be pierced so the two floors of the penthouse can have a stairwell in addition to the central elevator corridor.
It should be very obvious that there was a price to pay for a tower with tremendous distances between decks, relatively speaking. The tower necks down as it rises. This leaves the upper floors basically as donuts through which the load bearing structure must pass or in reality become an integral part of.