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Grove at Grand Bay



Terra Group teamed with celebrated Danish architect Bjarke Ingels of BIG Architects, to bring modern luxury to historic Coconut Grove, Miami’s oldest neighborhood. Terra and Ingels envisioned a residence that would evoke luxury, but also fuse it with distinctly contemporary design. Grove at Grand Bay is a 310-foot, 23-story condominium building located in Coconut Grove, Florida. It is the first truly twisting towers in the United States with floor plates that rotate every three feet up to 39° at every elevation from the 3rd to the 17th floors, and includes 40-foot interior spans with up to 20-foot cantilevers. The core consists of composite shear walls to resist the torque generated by the sloping columns.

Ingels’ design creates two gracefully twisting towers that appear to be turning to capture the view as they rise to the sky. It is also the first structure in Coconut Grove to have achieved LEED Gold Certification.

STRUCTURAL FRAMING SYSTEM

  • To develop the most cost-effective structural system solution that maximized the sellable area.

UNIQUE STRUCTURAL AND/OR ARCHITECTURAL DESIGN FEATURES

The true twisting nature of the columns posed a number of structural challenges that demanded a fresh, innovative approach. The foremost challenge was to resist torsion generated in the tower core due to the sloping column geometry. The horizontal component of the gravity load in the columns is resolved in the slabs by transferring it to the interior core shear walls, which are the only consistently vertical structural elements in the building. Additional horizontal thrust from all columns rotating in the same direction creates a large shear force in the tower cores. The magnitude of shear-forces in the tower cores due to self-weight was considerably higher than that generated by the design hurricane wind loads. To minimize the total horizontal shear force transfer into the core walls, a “hat truss” was introduced at the roof. The hat truss is comprised of a series of beams cantilevered from the cores and connected to all the columns. The hat truss collects superimposed dead load and live load delivering the “suspended” loads directly to the core as a vertical load component. This alternate load path reduced torsional forces in the core by approximately 30%.

The magnitude of the combined horizontal shear force from the building self-weight and the hurricane wind loads would require conventionally reinforced concrete shear walls to be 6 feet thick. In order to regain valuable real estate, a composite concrete shear wall and link beam system was introduced. The composite action between steel and concrete allowed a substantial wall reduction to 30-inches thick. Internal steel plates with thicknesses of up to 3.75-inches were required to achieve the overall wall thickness. Rolled steel sections replaced traditional reinforcing steel in the boundary element zones. The plates extend vertically for 15 floors with normal reinforcing steel continuing to the roof. To compensate for the considerable horizontal displacement, the tower floor plates are cambered rotationally as much as a 1/2-inch relative to the floor below for 75% movement due to the building self-weight. This allowed the tower to settle back to the design coordinates just before the hat truss reaches design strength.

To allow for maximum flexibility of the unit layouts, column-free interiors were provided. Resulting spans between the core and perimeter columns ranged up to 40 feet and balconies cantilevered up to 16 feet. A structural scheme was proposed with an 8-foot wide, 16-inch thickened slab around the core to allow a 10-inch thick post-tensioned slab to span the remaining distance. This provided a 12-foot clear ceiling dimension.

REASONS FOR CHOOSING REINFORCED CONCRETE

  • 100 ksi reinforcing steel (rebar) was used in the foundations to help mitigate congestion.
  • Composite 30-inch thick shear wall system was used to maximize sellable area and mitigate long-term creep due to the building’s twisting geometry.
  • Concrete strengths up to 12,000 psi were used.

Project Details

Location:

Coconut Grove, FL

Owner:

Terra Group, Coconut Grove, FL

Architect:

Bjarke Ingels Group (BIG Architects), New York, NY

Engineer:

DeSimone Consulting Engineers, Miami, FL

General Contractor:

Facchina Construction of Florida, LLC, Miami, FL

Concrete Contractor:

Capform, Inc., Miami Gardens, FL

Reinforcing Bar Fabricator:

Titon Builders Inc, Lake Park, FL

Total Project Size:

890,000 sq ft

Floor System:

Post-tensioned flat plate slab

Framing System:

Reinforced concrete

Award:

2016 CRSI Award Winner –
Residential Building Category

Photography:

DeSimone Consulting Engineers, Miami, FL
Bjarke Ingels Group, New York, NY

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