Striking a balance between value and cost was paramount to the architects and designers of the Zenith Towers, an innovative, supertall, mixed-use development that features an 80-story, 984-foot tower as the centerpiece of a 6.1-million-square-foot complex located on the waterfront of Busan, South Korea.
Before they could make history with the tallest reinforced-concrete residential structure in Asia, the development’s lead architects, DeStefano + Partners, had to abide by a number of concerns native to both the culture and conditions of the South Korean Peninsula.
“In Korea, there are common values within the residential environment that have driven most of the housing over the last 20 years,” said Scott Sarver, a principal at DeStefano + Partners. “The first is a southerly primary exposure for the living room and master bedroom—everybody wants to have sunlight in their unit. The second aspect is ventilation. No matter how much AC you put into a building, it’s culturally considered inferior to fresh air coming through an open window.”
To accommodate these market priorities, the architects, working with engineer Thornton Tomasetti, settled on a cruciform plan that configures bundles of seven to nine units per floor around each tower’s central structural column, which also houses the building’s service and mechanical elements. Passenger elevators are dispersed to remote cores within each leg of the tower, providing tenants with direct access to their particular unit bundle.
In addition to maximizing occupancy and intimacy, the cruciform plan orients each tower 45 degrees south, yielding southerly exposures and ocean views for all units while also allowing for at least two windows to open, giving each unit flow-through ventilation.
While cross-ventilation is an amenity to the tenants, the wind loading inherent in Busan’s typhoon-prone waterfront district suggested a hazard to the structure itself. To prevent the wind from organizing as a force at any one point along the building’s surface, architects built a system of irregular shapes and canopies into the building’s curtain wall, which is composed of unitized modular panels of extruded aluminum and low-e glass, with steel reinforcements added where peak conditions required.
“Theoretically, a perfectly round building would be the worst configuration possible,” said Sarver. “In that scenario, the winds would gather as a large force at the rear of the structure and suck those windows out.”
Underlying the design of any supertall building is a set of architectural fundamentals that govern the vertical aspect ratio of the lateral system. Simply put, the wider the stance of the base, the greater efficiency of the structure. To ensure structural integrity throughout the towers, designers focused on finding the point where the lateral wind-resistant system could be satisfied with the same quantities as the gravity system.
For the Zenith Towers, the architects employed a butterfly-shaped reinforced concrete core wall to maximize structural integrity with minimal material, granting the building an aspect ratio of 1:7. Additional support is provided by concrete outriggers at vertical intervals of 30 stories, which unifies the core wall with the structure’s perimeter, redistributing the load and minimizing differential movements such as post-construction creep and shrinkage.
The Zenith Towers’ delicate balance between the increased costs and difficulty associated with building up, and the enhanced value of unparalleled views and cross-ventilation, elegantly meet the unique criteria of the booming South Korean housing market.