25 feb 14  | Civil Engineering

Angled Facade Boosts Energy Efficiency

By Kevin Wilcox

The Federation of Korean Industries building, in Seoul, South Korea, features a high-performance curtain-wall system that deflects sunlight and generates energy.

The recently opened headquarters of the Federation of Korean Industries (FKI) in Seoul, South Korea, cuts an elegant, classic profile against the city’s skyline as one of the tallest buildings in the city. A closer look reveals an intricate, angled facade that not only bestows the building with distinction, but boosts sustainability and performance.

Adrian Smith + Gordon Gill Architecture LLP (AS+GG), of Chicago, designed the structure, which includes a contrasting podium building with organic curved lines, exposed steel ribs, and abundant glass. The tower contains the offices of FKI, an organization that represents more than 500 large companies in South Korea, including Hyundai, Samsung, and LG. The podium includes a conference center, meeting spaces, and a restaurant.

“FKI headquarters represents a new exterior wall typology that both integrates significant quantities of photovoltaic panels into the exterior wall and slopes the vision glass at an angle that generates self-shading, allowing less reflective glass to be used,” said Adrian Smith, FAIA, a partner of AS+GG, in a press release issued by the firm in January. “The result is a unique folded exterior texture that is both purposeful and distinctive.”

The Chicago office of Thornton Tomasetti, Inc., conducted the structural engineering of the tower, taking the design through the schematic phase before handing it over to Dong Yang Structural Engineers Company, of Seoul, South Korea, which served as the engineer of record for the project.

At 805 ft high, the building is the sixth-tallest in Seoul, according to a database maintained by the Council on Tall Buildings and Urban Habitats in Chicago. The tower has five below-ground levels, mostly parking, and nearly 365,000 sq ft of space above for the FKI headquarters and office space leased to other businesses.

The building was built on the site of the former FKI building, a smaller structure built approximately 50 years ago. As the project gained momentum, FKI relocated to temporary offices and the existing building was demolished to make way for the much larger structure, according to Robert Sinn, P.E., S.E., F.ASCE, FIABSE, LEED-AP. Sinn is a principal of Thornton Tomasetti and its building structure practice leader.

The foundation was constructed employing a top-down method, which is common in dense South Korean cities, where space for external foundation bracing is at a premium. Large circular piles were drilled down to bedrock and a thick concrete slab placed atop those piles.

“You put a very thick slab at the ground level that gives you a working platform from which you start to mine underneath and cast in steel plunge columns into the piles,” Sinn explains. “You start just underneath the [slab] and you mine out that soil, and then you put the first basement slab in. You keep working your way down to the bottom of the excavation. By doing that, then you don’t need any bracing for the perimeter slurry walls. You don’t need any external bracing or internal bracing. It’s just the slabs as you go down and the ground until it’s excavated. Additionally, the steel columns support the temporary loads from the tower construction above.”

The design team employed a concrete core for the tower, with composite perimeter columns, Sinn notes. At the first mechanical floor, located roughly one-third of the way up its height, steel outriggers extend from the core to the perimeter belt truss. “That reduces the deflection at the top of the building under wind load and [reduces] the forces in the walls,” Sinn says. “The idea [for] this tower was to make it repetitive and take advantage of the geometry.”

Wind loads on the structure were a key engineering challenge because the South Korean building codes require that the building be designed for a wind event with a return period of approximately 390 years, compared to 100 years in many other places.

“It’s not a high earthquake zone, so wind governs in terms of the size of the columns and the thickness of the walls,” Sinn says. The conservative wind codes increased some dimensions of columns and walls by as much as 20 percent, Sinn says.

This added complexity to what was already a challenging building to design. The engineers and architects wanted to minimize as much as possible the size of the columns in the structure for aesthetic reasons. But the team learned early in the project that type of the concrete that was available in the large quantities they required was rated at just 8,500 psi. “That’s not what we would call high-strength concrete here in the United States, or even the Middle East, for that matter,” Sinn says. “The ability to do higher-strength concrete usually has to do with the aggregate. If the aggregate is poor, then you won’t be able to get the higher strength. I don’t care how good your quality-control programs are—and quality control is quite good in Korea.”

To solve this challenge, the engineers specified composite columns with large steel plates embedded in the center of the concrete, functioning as “very, very large rebar,” Sinn says.

The facade comprises low-emissivity insulated glass, silver-anodized aluminum members, and customized photovoltaic (PV) panels that also serve as rain screens for the canted windows below. Sinn explains that the design team conducted extensive engineering analysis to place the PV panels in the most efficient locations on the structure, including the roof.

“The ideal angle of the PV panel placement on the roof was studied in detail,” noted Gordon Gill, FAIA, a partner of AS+GG, in the press release. “In a relatively unconfined space, PVs would normally be angled upward at 30 degrees but within the limited area of the roof, we determined that a 10 degree angle allowed for more panels to be installed closer together, minimizing the effect of the panels casting shadows on each other and ultimately producing more solar energy for the building.”

The PV panels are placed selectively, Sinn notes. “If you look closely at the building, they are only on the areas that would catch the sun. It’s not that we put them everywhere and some of them work and some of them don’t. So there is an upward angle of the wall that collects [sunlight] and there is a downward angle that reduces the glare inside the building. Adrian proposed those types of shading many, many years ago on other projects—before sustainability was even called sustainability.”

The smaller podium building—approximately 19,685 sq ft—included some of the most significant challenges of the entire project, Sinn says. “You have a lot going on in the podium building. You have unique geometry, you have exposed steel, you have a cable wall, and you have rationalization [of the geometry] of the curtain wall. We spent a lot of time on the podium and took that to a much higher level of design before we handed that off to our colleagues in Korea.”

To solve the challenge of the curved exterior glass panels, Thornton Tomasetti’s structural and building skin team employed parametric modeling and building information modeling (BIM) to simultaneously rationalize the steel-pipe rib structure and the insulated glass units (IGUs) enclosing the podium. The key was to create a definable and constructible structure, while holding the geometry to a shape that could utilize nothing but flat IGU panels.

The building officially opened in mid-January and has been well-received by the client and the public. “There is a nice dialogue between the podium and the tower,” Sinn says. “It is striking.”