ctbuh.org/papers Title: Structural Design of Taipei 101, the World's Tallest Building Authors: Dennis Poon, Managing Principal, Thornton Tomasetti Shaw-Song Shieh, President, Evergreen Engineering Leonard Joseph, Principal, Thornton Tomasetti Ching-Chang Chang, Project Manager, Evergreen Engineering Subjects: Building Case Study Structural Engineering Keywords: Concrete Outriggers Structure Tuned Mass Damper Publication Date: 2004 Original Publication: CTBUH 2004 Seoul Conference Paper Type: 1. Book chapter/Part chapter 2. Journal paper 3. Conference proceeding 4. Unpublished conference paper 5. Magazine article 6. Unpublished © Council on Tall Buildings and Urban Habitat / Dennis Poon; Shaw-Song Shieh; Leonard Joseph; Ching- Chang Chang Structural Design of Taipei 101, the World's Tallest Building Dennis C. K. Poon, PE, M.S.1, Shaw-song Shieh, PE, SE, M.S.2, Leonard M. Joseph, PE, SE, M.S.3, Ching-Chang Chang, PE, SE, M.S.4 1Managing Principal, Thornton-Tomasetti Group, New York 2President, Evergreen Consulting Engineering, Inc., Taipei 3Principal, Thornton-Tomasetti Group, Irvine, California 4Project Manager, Evergreen Consulting Engineering, Inc., Taipei Abstract At 101 stories and 508 m above grade, the Taipei 101 tower is the newest World’s Tallest Building. Collaboration between architects and engineers satisfied demands of esthetics, real estate economics, construction, occupant comfort in mild-to-moderate winds, and structural safety in typhoons and earthquakes. Its architectural design, eight eight-story modules standing atop a tapering base, evokes indigenous jointed bamboo and tiered pagodas. Building shape refinements from wind tunnel studies dramatically reduced accelerations and overturning forces from vortex shedding. The structural framing system of braced core and multiple outriggers accommodates numerous building setbacks. A secondary lateral load system of perimeter moment frames and special core connections adds to seismic safety. Column axial stiffness for drift control was made practical through steel boxes filled with high-strength concrete. Occupant comfort is improved by a massive rooftop pendulum Tuned Mass Damper. Pinnacle framing fatigue life is enhanced by a pair of compact spring-driven TMDs. The soft soil subgrade required mat foundations on bored piles, slurry walls, and a mix of top-down and conventional bottom-up construction with cross-lot bracing. The project illustrates the large and small design decisions in both architecture and engineering necessary to successfully complete a major building in a challenging environment. Keywords: vortex shedding, high-strength concrete, tuned mass damper, outrigger, fatigue 1. Introduction 2. Tower Height Every project has a list of challenges, but for Taipei The first challenge was the height. Building stories 101, the new world’s tallest building, that list is longer come at an ever-increasing cost, as if the new story is than size alone would imply. Starting with a design added at the bottom of the building. That reflects the height of 508 m [check], it also includes the overall and need for supporting all the floors above, for elevator localized load effects from frequent and extreme shaft and stairwell space, and for mechanical, electrical, typhoons; potentially severe earthquakes; and difficult plumbing and fire protection risers. The economic subsurface conditions, including an inactive fault height limit occurs where the added cost of a floor through the site. Occupants must be both physically exceeds the added rent the floor will bring. Prior to and psychologically comfortable with the design, even Taipei 101, the tallest building on the island of Taiwan during high winds and extreme events. Rising from a was the 85-story T&C Tower in Kaohsiung. The major dramatic, landmark-quality retail mall, the tower has a jump in height resulted from the desire of project profile unlike that of any previous skyscraper: a investors, several financial firms, to occupy space in a tapering base topped by a series of flared segments. landmark building. Projected office space demand of And a couple of temblors rattled the 200,000 m2 (2.1 million square feet) [check] and partially-completed structure, reminders of the individual floor areas based on general office layout challenges the design must address. Meeting all these standards led to a height of 101 stories. Another challenges through studies, design and construction 200,000 m2 occurs in a podium of retail space was an unforgettable experience for all involved. surrounding the tower base and basement parking. 3. Foundations Contact Author: Dennis Poon, PE The second challenge was the site. Soft rock occurs Managing Principal, Thornton-Tomasetti Group 641 Avenue of the Americas, NY, NY 10011 USA beneath 40 to 60 m of clay and stiff colluvial soil. The Tel: 0011.917.661.7800 Fax: 0011.917.661.7801 design required a 21 m deep basement, while ground e-mail: [email protected] water is usually 2 m below grade and potentially at CTBUH 2004 October 10~13, Seoul, Korea 271 grade. Based on extensive investigations by compared to a straight shaft, if the structural system Taipei-based Sino Geotechnology Inc. and scheduling engages the perimeter columns. The transition from requirements, five major components were used to lower pyramid to upper modules is highlighted by create two different foundation systems. One slurry medallions based on ancient Chinese coins. See Fig.1. wall 1.2 m (4 ft) thick surrounds both tower and podium; its 47 m (154 ft) depth cuts off ground water and provides toe embedment well below the 21.8 to 23.5 m (72 to 77 ft) excavation depth. Each podium column bears on a single 2 m (6.5 ft) diameter drilled pier. Sockets 5 to 28 m (16 to 92 ft) into bedrock resist net uplift from a podium pressure slab resisting buoyancy. The single-pier design permitted ‘top down’ basement construction: a floor was cast to brace perimeter walls, then a story of excavation proceeded below it. Superstructure framing was erected at the same time. As a result, the retail podium opened about a year before the tower topped out. A second slurry wall, enclosing just the tower footprint, was supported by steel cross-lot bracing as excavation proceeded to full depth. the walls were braced to accommodate construction sequencing. A continuous reinforced concrete mat 3 to 4.7 m (10 to 15 ft) thick transfers load from discrete column and shear wall load points to a distributed pattern of 380 drilled piers, 1.5 m (5 ft) in diameter, spaced 4 m (13.12 ft) on center in staggered rows to resist gravity loads between 10.7 and 14.2 MN (1500 and 2000 kips). Using steel framing minimized building weight, helping to reduce Fig. 1. The Taipei 101 profile shows a truncated pyramidal base foundation costs. topped by eight, 8-story flaring building modules, a narrower equipment/observation deck module and a steel-spined spire 4. Building Vertical Shaping The third challenge was the tower shape established 5. Plan Shaping for Wind by architect C.Y. Lee. Well-regarded in the region and The fourth challenge was a high wind environment. experienced in tall buildings, including the T&C Tower Tall, slender chimneys and skyscrapers experience designed with Evergreen, Lee’s building shape for alternating crosswind forces due to vortex shedding: Taipei 101 provides an instantly recognizable symbol wind passing the object separates from side faces in of Taipei and Taiwan. The repeating modules were alternating whirlpools. When vortex formation set by inspired by the joints of indigenous bamboo and the wind speed and building dimensions coincides with tiers of pagodas; each module has a narrower base and building period, large forces can result. Here a typhoon a wider top as if a flower opening to the sky. Each with 100 year return period brings winds of 43.3 m/sec module has eight floors, and eight modules form the (97 mph) averaged over 10 minutes at a height of 10 m majority of the tower’s height. In the Chinese spoken in (33 ft). This is similar to a three-second gust of 67 Taiwan, ‘eight’ is a homonym with ‘wealth,’ making it m/sec (150 mph). It can excite a skyscraper with a very appropriate feature for a financial center. A ninth crosswind forces much greater than those normally module that tops the main shaft and supports an used for design. During a wind tunnel visit by C.Y. and architectural spire has a smaller footprint but matching the authors, RWDI demonstrated that a square tower wall slopes. Below the repetitive flared modules, a 25 with sharp corners creates large crosswind excitation. o story base shaped as a truncated pyramid provides Rounded and chamfered (45 ) corners reduced lateral improved overturning resistance and lateral stiffness response, but a ‘saw tooth’ or ‘double notch’ corner 272 CTBUH 2004 October 10~13, Seoul, Korea with 2.5 m (8.2 ft) notches achieved a dramatic reduction. See Fig.2. Architect Lee understood the significance of this shape and incorporated it into the upper module corners from that point on. See Fig.3. 6. Lateral Load Resisting Systems Considered While low- and mid-rise buildings can rely on an interior core of shear walls or bracing to provide overall tower stability, for the tallest of skyscrapers the full building floor plan width and depth is used to Fig. 3. A close-up of the tower corner clearly shows the ‘sawtooth’ treatment above Floor 25 for wind vortex reduction. through ‘outrigger trusses’ with top and bottom chords incorporated within the framing of two adjacent floors and diagonals through occupied space, preferably mechanical or storage rooms. In this ‘megaframe,’ outrigger trusses and outrigger columns help stabilize the narrower core. The perimeter framing is more open. Outrigger effectiveness depends on location and on outrigger column stiffness. Belt trusses just above each Fig .2. Wind tunnel cross-wind base moments: module setback gather and transfer perimeter weight to Top- square-cornered model with damping at 1% of critical.