Architect: Zaha Hadid Architects & O’Donnell Dannwolf & Partners Architects
Engineer: DeSimone Consulting Engineers
Construction Management: Plaza Construction
General Contractor: Plaza Construction
Concrete Contractor: CAPFORM Inc.
Total Project Cost: $450 Million
STRUCTURAL FRAMING SYSTEM
The tower’s exoskeleton is designed to carry gravity loads of the tower and to withstand high-velocity, hurricane wind forces. A traditional approach to withstand wind pressure on 709-foot tower would have required significantly thicker shear walls resulting in less sellable area for the developer. To increase the project’s profitability, a non-traditional approach was required to minimize the thickness of shear wall.
As a solution, DeSimone utilized the tower’s sculptural features as a structural exoskeleton. The modified structural element was employed as a bracing system in tandem with traditional shear walls to achieve more efficient, thinner shear walls. After several rounds of discussion and coordination with Zaha Hadid Architects, the exoskeleton’s profile was adjusted and optimized to form a hybrid bracing pattern. The shear walls and exoskeleton columns were poured with the high-strength concrete – 12,000 psi from base to mid-height and a 10,000 psi for the remaining height.
UNIQUE DESIGN FEATURES
To further optimize and reduce sizes of the shear walls and the exoskeleton columns, DeSimone used the concrete’s full modulus of elasticity in the design. However, concrete mix design with the local limestone aggregates from Florida quarries does not yield the full modulus of elasticity as required by ACI 318. Instead, granite aggregates were imported from outside Florida state to achieve the full modulus of elasticity. Throughout the project, Grade 75 steel was used for vertical reinforcement. Grade 100 steel was used in places of heavy steel congestion.
The complex shape of exoskeleton structure proved difficult to cast and to form as required by the architect. It was also determined, after initial cost studies, that the traditional approach would not be cost effective and could add significant time to the overall project schedule. Following a series of studies, the project team decided to use GFRC panels as permanent formwork to resolve the casting and forming issues, and to avoid compromising the shape of exoskeleton structure. This approach was implemented from the 15th floor to the pinnacle of the structure.
Below the 15th floor, many of the exoskeleton’s architectural forms are quite large, measuring 25-feet-long and 5-feet-thick. For these lower levels, the shapes were structurally simplified into rectangular sections. The simplified shapes were then covered with the GFRC cladding. This approach eliminated approximately four months from of the project schedule.
For the interior environment of One Thousand Museum, Zaha Hadid envisioned column-free layouts to deliver unobstructed views of the surrounding city and of the Atlantic Ocean. However, initial layouts included numerous interior columns to maintain a slab thickness of eight inches. Through discussions with the entire development team, a thicker slab was implemented to require only two interior columns. The resulting floor plan includes clear spans from core to glass of up to 45 feet as desired by the architect.
Design of the structure’s foundation system was also a challenge for the project team. Even after reducing the typical floor thickness to 11 inches, the slabs remained thicker than a traditional 9 inch thick slab. The additional thickness resulted in higher gravity loads on the foundation system. In addition to gravity loads, the project site is located just south of a 48-story high-rise tower whose foundation system sits only 2-inches away from One Thousand Museum’s property line. All considered, the selected foundation system would have to ensure the least possible tower settlement, to prevent major impact on the adjacent property.
Based on the subsurface conditions and the preliminary soil analysis, the 30 inch diameter, 165 foot deep Auger Cast-In-Place (ACIP) piles were selected. The ACIP had a capacity of 1,050 tons in compression and 250 tons in tension. The tower is supported on a 12-foot-thick deep mat foundation measuring 147-feet-wide by 149.5-feet-deep. The mat foundation is supported on 227 30-inch ACIP piles and it is expected to settle only 2.5 to 3.5 inches in a dish like pattern with the greatest magnitudes in the core. These magnitudes diminish with increasing distance from these areas.