Stacked Cubes on a Spindle – No Simple Feat: Ministry of Taxes, Baku
Session: G: Structural Engineering Award: Part 1
Hi Sun Choi
Senior Principal, Thornton Tomasetti, Inc.
New York City
Vice President, Thornton Tomasetti, Inc.
New York City
The Ministry of Taxes tower features five stacked cubes that cantilever independently from a circular central core. Each cube holds five office floors, and a column-free green roof terrace provides a distinct separation from the cube above. Moreover, each floor plan is rotated 1.2 degrees with respect to the floor below, resulting in an astonishing 40-degree rotation overall from bottom to top that optimizes both solar orientation and views.
The tower’s unique features and iconic design posed several interesting challenges. First, the separate stacked cubes and terraces between them required picking up eight perimeter columns on 10-meter-long transfer trusses cantilevering from the central core. This innovative design solution allowed the vertical load to be carried through steel diagonal web members, while the induced moment from the truss is resisted by a force couple from in-plane tension and compression forces in the slabs, integral with the truss’ top and bottom chords. This reflects realistic compatible behavior at chords and slabs.
Long span, column-free corners at each floor presented another challenge. The design incorporated three different construction materials—reinforced concrete, structural steel, and post-tensioned tendons—that required close collaboration between design and construction teams, especially for the transfer steel truss locations and the special detailing needed at the transfer floors. The construction sequence presented an additional challenge. Erecting a structural steel truss alone was not sufficient to provide a complete load path for the column transfer. At the bottom two floors of each cube, reinforced concrete slabs were placed, working as tension-compression rings and post-tensioned beams, stabilizing the transfer system. This required extensive coordination, as the temporary shoring below each cube needed to be able to support the wet concrete weight of two stories.