|Written by Carla Swickerath, Studio Daniel Libeskind and Peter Tillson, Arup New York|
|Posted October 2011|
|This paper was originally featured as a case study in CTBUH Journal 2011 Issue IV and is also available as a PDF download.|
Other Featured Tall Buildings
“In South Korea, there is an emphasis on family and social relationships. High-density residential developments are preferred because they support a strong sense of community.”
T1: 273 m (895 ft);
T2: 292 m (958 ft);
T3: 205 m (674 ft);
T1: 66; T2: 72; and T3: 46
Hyundai Development Company
Studio Daniel Libeskind
Arup; Dong Yang Structural Engineers
Hyundai Development Company
Saegil E. & C; Ctopos;
Wallplus; Yung-Do Engineering; LPA
|Heundai I'Park, Busan © Studio Daniel Libeskind|
The Haeundae I’Park is a 511,805-square meter (5,509,000-square foot) high-density mixed-use development in Busan, South Korea which includes three high-rise residential towers (66, 72 and 46 floors) and a total of 1,631 units. A 34-floor luxury hotel, a 9-floor office building, and a 3-floor retail building have been composed on a landscaped, waterfront site in the second largest city in Korea. Busan, a rapidly growing city with approximately 3.6 million residents, is located on the southeastern tip of the Korean peninsula. It is a bustling port city and a vacation destination, with a dramatic combination of both mountains and beaches as its natural setting.
The I’Park development creates a new, forward-looking image for The Hyundai Development Company (HDC) and a new vision for residential living in Busan. Built on a landfill site along the waterfront, the three residential towers soar to 292 meters (958 feet), 273 meters (895 feet) and 205 meters (674 feet). The highest tower became the tallest residential building in Asia on completion. Essential to the design of the Haeundae I’Park complex is the integration of the development into the Haeundae Marina city site to the west. The marina’s development by the same owner (HDC) will be part of the residential amenities for the project and will serve as a public attraction for visitors and residents.
|Aerial View © Hyundai Development Company|
The Korean residential market is unique and the design of the Haeundae I’Park had to respond in a meaningful way to the specific cultural and economic issues. In South Korea it is considered desirable to live in cities and, as with most major urban centers, land prices are incredibly high. Large scale, high-rise developments are the most efficient and profitable way to provide housing that meets the demands of the market. Therefore the market has very rigorous efficiency standards that are challenging to achieve. Design solutions need to be creative and practical to maximize land values. The market’s emphasis on ownership also drives the quality, diversity and quantity of residential units which become more than just a living space, but also a major investment for the future. The quality of design, sense of community and amenities provided not only make for very attractive, livable residential developments, but become assets that help the units hold their value over time.
The main challenge of the project was to create a balanced composition with maximum views and livability with a large program on a very dense site. The design had to meet rigorous efficiency expectations and moderate construction costs while maximizing sweeping views of the ocean, the marina, the mountains, the Gwang-An bridge and the landscape and the city of Busan.
To find innovative solutions, multiple strategies for the massing of the program on the site were studied. Instead of simply extruding the typical building footprints to their maximum heights, the footprints of the towers are made of a sculpted shape in plan, the heights are varied and the profiles are tapered to create a three-dimensional composition on the horizon. The varying heights of the buildings help to break down the overall massing of the residential tower complex. Instead of simply extruding the footprints of the buildings to an equal height, the design redistributes the allowed massing and height of the towers to create variation in the composition of the towers while meeting the maximum FAR for the development.
These strategies not only give the project and the city of Busan a new landmark and a new image of residential development, which in Korea is traditionally quite formulaic, they also help maximize the view corridors of all the apartments as well as bring the most light possible into the site and the developments beyond the site. Redistributing the massing makes the very large development seem more slender on the skyline. Also, the varied forms create unique and exciting spaces between the buildings that add interest and variety to the entire development from inside and out.
|| Site mass diagram © Studio Daniel Libeskind|
|Central landscape are © Studio Daniel Libeskind|
Busan is one of the windiest cities in Asia and the dramatic site is right on the ocean’s edge. The towers will bear the full force of the yearly typhoons coming from the southeast.
The Korean Building Code (KBC), similar to almost all wind codes around the world, does not account for across-wind dynamic responses or the sheltering or enhancing effect of other nearby buildings. This is often a reason for wind tunnel testing, even in the case of a standard building shape. The unique building shapes were an additional reason to wind tunnel test (see Figure 5). Additionally, typhoon-strength winds dominate the wind climate of the southern Korean peninsula for longer return periods. These typhoon winds are an important consideration in the strength design of new developments. For the shorter return period winds which affect the serviceability design of structures, the more frequently occurring synoptic type winds needed to be considered.
The towers were constructed using reinforced concrete and are supported on foundations at the base of the 6-story deep basement, which covers the whole site. The tapering tip portion of each tower is framed in structural steel.
The typical residential floor slabs are 250 millimeters (10 inches) thick with no drop panels or column capitals. Mechanical slabs are 350 millimeters (14 inches) thick. Beams are provided around significant slab openings. Columns are generally square or rectangular to coordinate with the planning and were sized based on maximum 60 MPa concrete.
Outriggers were initially conceived in concrete to maximize stiffness, but were changed to steel, because coordination with the mechanical equipment was simpler and it is easier to release and relock the steel outriggers to release creep and elastic stresses caused by differential shortening of the columns and core. The design incorporates double-story belt trusses at mechanical levels connecting to the outriggers. The outriggers are located at one-third and two-thirds of the tower’s height (see Figure 7). The tapering tip of each tower is also designed as a structural steel frame.
The lateral structure of the tallest tower is highly stressed under the design level wind event. The design utilizes slabs in the lateral system to enhance the lateral stiffness of the tower and help control wind drifts. High reinforcement ratios in the lower level core walls and steel sections in some link beams were also required.
Additional vertical steel was provided in the core walls to maintain the effective wall section’s axial stiffness to the high tensions caused by the wind loads. An iterative analysis procedure was adopted. Axial forces and moments in each wall pier were extracted from the initial analysis models and the piers were analyzed for cracking using Oasys ADSEC. In cases where the wall was found to have a cracked section modifier lower than the value of 0.8 assumed in the analysis, the steel percentage was increased to reduce the amount of cracking, and increase the effective E of the section. Overall, the steel percentage was increased to maintain the assumed stiffness modifier of 0.8.
The extensive six-level basement serves all buildings and houses service and delivery functions and parking. Away from the building footprints the column grid is a regular 8-meter (26.2-foot) or 8.2-meter (26.9-foot) grid with a repetitious, simple construction to allow for maximum construction speed. The basement slab construction for suspended levels is a 250-millimeter (10-inch) reinforced concrete flat slab construction with drop panels. The plaza level slab atop the basement parking garage structure is designed to support significant soil and traffic loadings acting together.
An existing slurry wall from a prior development start was integrated into the basement design and supplemented by a new slurry wall. The basement construction is adjacent to the sea and extends substantially below sea level. The foundations for the towers consist of closely-spaced caissons supporting a large mat foundation.
The façade design for the project had two major design criteria: high performance and cost effectiveness. To that end, the project employs a hybrid façade system that has the look of continuous glazing on the exterior like a traditional curtain wall, while performing like a window wall system spanning from floor to floor. The hybrid curtain wall system is more effective in cost, load transfer and deflection resistance than a typical curtain wall system that spans multiple floors.
The envelope thus utilizes a glazed exterior wall system with overall thermal transmittance of 1.68 W/m²•K and shading coefficient of 0.41. The system is made up of 24-millimeter (0.94-inch) thick reflective Low-E insulating glass units and an insulation aluminum bar system that is anchored to the building structure at each floor level. An interior glazed system is utilized for ease of installation and maintenance from each floor level.
|Curved façade © Studio Daniel Libeskind |
Together with a strategy to harmonize the design with the environment, landscape, and community of residents, the design focuses on making a sustainable, environmentally-responsible residential development with a green building certification accredited by the Korea Land & Housing Corporation. A few examples of the means used to achieve the certification are design components like water tanks for rainwater collection that have been installed in each tower; sustainable, eco-friendly materials used to minimize strain on the environment; a high performance building envelope; a green roof system; and biotope (water/land) that will provide a healthy, livable environment for the inhabitants. The project was also designed with co-gen and centralized systems. For the interior environment, each residential unit is equipped with individual temperature control systems and built with materials containing less toxic substances. In each unit there are different sustainable design elements including radiant floor heating, a heat recovery ventilation system, high-efficient condensing boiler and ceiling cassette type of air conditioner with outdoor units for higher efficiency. Space for plantings in the interior public spaces and energy control systems in the public areas are also utilized to preserve energy.
Many of the sustainable approaches not only conserve resources, but provide a cost benefit to the client with reductions in the operational costs of the buildings. In order to minimize energy loss caused by stack effect, the vertical transportation system was designed with many energy saving elements. Three different zones (parking shuttle, low-rise and high-rise) were planned to reduce the vertical air flow. In addition, air-tight vestibules with revolving doors are installed on all ground level lobbies to prevent air influx. On each level, the common corridors were divided into smaller zones with doors to block horizontal air movement. As a result of these strategies, a 4% cost benefit is anticipated to be achieved for public areas. In addition, elements like lighting systems in the public area are equipped with timers and high efficiency lamps that reduced the operational costs for lighting by 7–15%.
The Haeundae I’Park is part of a new era of residential living in Korea. An essential lesson learned from the project is that inspiration in design need not be fettered by formulaic requirements. Design solutions had to be particularly innovative and creative yet practical and efficient to meet all of the necessary standards. In fact, the demanding criteria were seen as a challenge and a source of inspiration and a motivation for inventiveness from the design team.