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Concrete honeycomb façade: when material met structure

The interesting thing about metamaterials is that it is the structure rather than the material that saves the day. However, it is even better when the material and the structure complement each other. The Honeycomb, designed by BIG, is a building that shows the importance of the interaction between material and structure. The concrete façade consists of private balconies with a pool, weighing between 108,000 and 269,000 pounds (48,000-122,000 kilograms) each, including pool water. The shape of these balconies, which are hexagonal, is crucial.

The Honeycomb is a luxury eight-story condominium currently under construction in the Bahamas. In addiction to the weight of the balconies, they also cantilever up to 17.5 feet (5.3 meters) from the structure.

Central to the Honeycomb’s design of is the use of a specially engineered concrete “superslab” which is able to cantilever over 17 feet (5.2 feet) without wall brackets below. This was achieved by reducing the slab’s weight while maintaining its strength and stiffness. To control deflection and reduce self-weight, 12-inch (30 centimetres) diameter tubes were embedded in a 17-inch (43 centimetres) thick conventionally reinforced roof slab. These voids hollow out the slab, reducing its weight and increasing the section’s overall efficiency. This step eliminated the need for a post-tension slab, further reducing the overall weight and reducing the cost of the project.

The balcony decks themselves are constructed from a 13-inch (33 centimetres) thick conventionally reinforced slab. Each unit has a private pool, which is integrated into the balcony slab. To accommodate the volume of the pool, the balcony slab folds down at the deepest point of the pool. This coincides with the partition wall below, which functions as a beam to support the load of the water.

Because of the staggered partition walls and varied façade, these shear walls sometimes connect to a structural column, supporting the slab above and below. The 18-inch (45 centimetres) thick concrete shear walls not only increase structural support, but also join into the sloped pool floors in order to form the hexagonal honeycomb structure.

Because of the Honeycomb’s structural system, conventional materials could be used. To ensure durability, the initial soluble chlorides in the concrete mix were limited, a tight water-cement ratio was provided, and a concrete cover over the reinforcing steel was added. Finally, for further protection, an integral waterproofing admixture and surface applied coating were also used.

Photos: BIG / DeSimone Consulting Engineers (via Archdaily)