Download The Price of Height Lofty Challenges

S H A P I N G T H E WI N D A N D T H E FA C E O F TO M O R R O W ’ S S K Y S C R A P E R S
T RACY KIJEWSKI-CORREA
We marvel at the skill of the ancient builders, at the sheer scale in which they cast their masterpieces, setting a
precedent that we to this day still follow: using our built environment as a testament to our civilization, a tribute to
our technological prowess and financial strength. Throughout time, civilizations have relied upon structures of everincreasing height to celebrate their progress and prosperity. Today, that same spirit is embodied in the race towards
the heavens undertaken by modern skyscrapers, which have come to define the thriving metropolis worldwide.
The Price of Height
The rapid growth of cities during America’s infancy necessitated the efficient use of real estate, forcing buildings
upward, but the lack of sufficient materials to carry the added loads of upper floors placed limits on these designs. In
fact, the skyscraper was not a practical undertaking until the advent of electricity, fireproofing, and most
importantly, E.G. Otis’s elevator. These components were first synthesized in 1885 in the first metal-framed
structure by William Le Baron Jenney to yield the Home Insurance Building of Chicago. From this first skyscraper,
America’s skyline has grown with materials and construction technologies, yielding structures towering at amazing
heights. Unfortunately, as a consequence of their lightweight design, these structures often suffer from increased
flexibility and a lack of sufficient damping. These deficiencies have not left them well suited for the new challenges
that await them at higher altitudes in the complex environment created by wind, where the interaction between the
wakes of neighboring structures can play havoc with today’s skyscrapers.
Lofty Challenges
With every advance in height comes a new challenge, such as insuring that the structure remains functional under
the action of wind. Even though the structure may satisfactorily carry all the lateral loads, it still must satisfy
serviceability requirements in the form of drift limits and perception criteria, as occupants often feel discomfort in
the form of dizziness, headaches, and nausea resulting from the accelerations of the building due to the dynamic
1
nature of wind. Traditionally, the use of more efficient structural systems permitted designs to accommodate the
challenges imposed by their increased height; however, even with the use of core and outrigger systems and bundled
and braced tubes to increase stiffness and limit lateral and torsional motions, the final design may still be forced to
consult additional avenues to satisfy occupant perception criteria.
Shaping the Wind
Just as the aerospace industry has tailored its designs for optimal performance in wind, the design of tall buildings
can use these same considerations to eliminate the problem of wind-induced vibrations at its source. While there
may be reluctances that particular aerodynamic modifications will detract from the aesthetics of the structure, the
following examples illustrate that these considerations can be integrated into the design of tall buildings without
sacrificing their appearance and often creating a signature for that structure.
Modifications to Corner Geometry and Building Shape
The inclusion of chamfered corners, horizontal slots and slotted corners have been found to considerably reduce the
response of buildings, in comparison to the performance of a basic square plan1, with these improvements becoming
more marked as the corners are progressively rounded. The first series of hand sketches shown in Figure 1 illustrates
the spectrum of corner modifications, confirmed by wind tunnel testing to markedly reduce rms displacements. In
particular, the chamfering of corners has proven especially beneficial in the design of the Mitsubishi Heavy
Industries (MHI) Yokohama Building in Japan, following realization that the wakes of peripheral tall buildings
would induce excessive response. While the aerodynamic superiority of this configuration is evident from wind
tunnel studies, the modification also improved the appearance of the structure, adding additional depth and contrast
to the its façade, with the vertical shadows created by this chamfering effect eliminating the redundancy of the
horizontal elements along its face.
1
Kwok, K.C.S. (1995) “Aerodynamics of Tall Buildings,” Proceedings of Ninth International Conference on Wind Engineering, New Delhi.
Setbacks and Tapering
Some of the most graceful and notable structures incorporate a series of setbacks and tapering in their design,
accentuating the height of the structure, but also serving practical aerodynamic purposes. Improvements in response
have been observed in buildings that vary their cross-sectional shape with height or which reduce their upper level
plans through tapering effects, cutting corners, or progressively dropping off corners with height2. The sketches in
Figure 2 compare the response of a building that reduces its plan with height to one without such modifications,
illustrating a marked reduction in response. In fact, the more sculptured a building’s top is, the better it can minimize
wind responses, as evidenced by the 450 m Petronas Towers. The repeated use of multi-level setbacks to taper the
towers and reduce their plan with height provided a sleek and elegant appearance while, still allowing the integration
of Islamic geometric patterns in the cross-sectional shape to merge cultural imagery with modern architecture.
Further evidence of the aesthetic benefits of aerodynamic modifications is provided by the 421 m Jin Mao building,
which uses setbacks to gently taper its façade. While the setbacks draw the eye’s attention up the structure towards
its crown, they more importantly gradually reduce and redefine the shape of the structure at the upper levels, where
the effects of wind are most critical. The structure is literally transformed by subtle setbacks from a square plan to a
complex cruciform, as if slowly twisted from above by an unseen hand. The performance under wind is further
enhanced by shifting the ornate crown of the tower about its central axis, as reiterated in Figure 3. The end result is a
breathtaking structure that not only pays tribute to the Chinese culture, with its ornate tiers reminiscent of the ancient
pagodas, but can also withstand typhoon winds, in part due to the judicious choice of lateral system and the use of
aerodynamic tapering.
Through-Building Openings
The inclusion of openings completely through the building, particularly near the top, provides yet another means for
improving aerodynamic response, significantly reducing vortex-shedding forces3. This design strategy was
2
Shimada, K. and Hibi, K. (1995) “Estimation of Wind Loads for a Super-Tall Building (SSH),” The Structural Design of Tall Buildings, John
Wiley and Sons, 4: 47-60.
3
Dutton, R. and Isyumov, N. (1991) “Reduction of Tall Building Motion by Aerodynamic Treatments,” J. of Wind Engineering and Industrial
Aerodynamics 36(2): 739-747.
integrated into the proposed world’s tallest building, the Shanghai World Financial Center, which features a diagonal
face that is shaved back with an 51 m aperture to relieve pressure at the top of the building, shown in the fourth
figure. The utilization of both the opening, and shifting and decreasing the cross section with height, essentially
tapers the 460 m tower and reduces the wind loads on the structure, as evidenced by the dramatic decrease in the
spectral peak as a result of the addition of through-building openings. The shaving of the face of the structure
provides a unique shape to the building’s upper plan, yielding a smooth transition from the entrance toward the
captivating opening above. Unfortunately, this design has resulted in a loss of rental space in these upper floors,
though in the case of the World Financial Center, this feature now serves as a priceless trademark for the building.
However, the presence of openings does not have to be as drastic as in this example, as research has also established
the benefits of configurations of vents, slits or smaller openings that do not compromise as much rental space.
Tomorrow’s Vision
With each step towards the heavens man becomes more aware of his limitations, yet with much tenacity, finds
innovations to overcome them. As we embark upon a new millennium in tall building design, the significance of
dynamic wind effects becomes increasingly important, presenting a new challenge to conquer in the quest for new
heights. While the advancements in auxiliary damping devices, which have sparked great interest in Japan, provide
one viable solution, it is my intent to reiterate the significance of the merger between traditional structural
engineering and aerospace fundamentals as equally viable mitigation strategies. The next generation of skyscrapers
must build upon the foundations laid by the innovative structures discussed in this work and consciously incorporate
aerodynamic modifications into their designs, using the wind tunnel as a tool to optimize the building’s form, from
the perspectives of serviceability and occupant comfort. As these prototype structures have illustrated, the simple
modifications of corners and the more sophisticated tapering and progressive alterations of plan can achieve
stunning visual presentations, while achieving equally stunning performance objectives, when coupled with a
judicious choice of structural system. In this respect, tomorrow’s structures can truly integrate the advancements in
structural and aerospace engineering without sacrificing architectural vision, as we inch every bit closer to the gods.
Proposed Travel Itinerary
Tracy Kijewski-Correa
Man has always erected tributes to the gods, including pyramids, temples and cathedrals with
visions fixated skyward; however, today’s monuments to the sky are meant for glory of a
different kind. The skyscraper now serves as a trademark, a signature for immerging cities that
catapults them onto the international scene. They are monuments of power, prosperity, growth,
and ultimately, glory. Just as the Empire State Building and Chrysler Building have become
synonymous with New York City’s growth and prominence, the economic expansion in Asia has
resulted in numerous signature structures, comprising nearly half of the twenty-five tallest
buildings in the world. These structures, like Asia itself, represent the transition of ancient
culture of the East to a more global culture that incorporates themes from the West, with many of
these structures embracing traditional cultural and geographical features in their design. This
union of East and West has resulted in a unique urban architecture that will be showcased by the
following itinerary, featuring three Asian cities, with visits to particular structures motivated
herein.
I. Kuala Lumpur, Malaysia (2 Days)
The rapid economic expansion of Kuala Lumpur has led to the development of numerous
signature structures, including the World’s Tallest Buildings (according to some definitions),
incorporating cultural traditions and modern architecture. A two-day documentation of this city’s
architecture will feature recent projects such as Plaza Rakyat and the Telekom Malaysia
Headquarters, as well as the following sites:
• International Airport
Completed in 1998, this series of shell and tent structures mimic the sensations of the outdoors,
as if passengers are moving beneath the shade of a Malaysian forest, with the columns
supporting this roof structure echoing this motif. Kisho Kurokawa has created a concept that
synthesizes an airport, itself a symbol of growth and globalization, with the traditional face of
Malaysia, one of lush forests that once covered much of the countryside.
• Petronas Towers
Cesar Pelli conceived this gateway to Kuala Lumpur as the ultimate expression of Malaysia’s
emergence in the international marketplace. The stainless steel twin towers, joined by a
pedestrian sky bridge, an engineering feat in itself, echo this gateway effect. Further cultural
significance is provided by floor plates within the structure, which integrate shapes from Islamic
geometric principles. These same principles resurface in the ornate cross sectional shape of the
towers, each topped by shimmering spires. Since Lao Tse teaches that reality actually lies in the
void of an object and not in the walls which surround it, the towers hold an even deeper
significance in the context of Malaysian culture, as the space between these giants is symbolic of
this spiritual reality which can merely be transversed but not filled by man, symbolized by the
lone sky bridge.
• Malayan Bank Headquarters
The merger between traditional culture and the modern skyscraper has been critical in Asian
developments. Hijjas Kasturi’s design typifies this through the use of sloped roofs, which
resonate the roofing systems of traditional Malay houses. This theme is reiterated in the entrance
canopies with the multi-layered roof, a symbol of prominence and wealth, while the vertical lines
of the building remain true to the stilt-like foundations of traditional Malaysian housing. The
monotony of these vertical lines on the building’s face is interrupted by transfer girders at two
levels in the building, illustrating the architectural utility inherent in structural components.
• Luth Headquarters
Hijjas Kasturi also created this visually stunning structure featuring a tube in tube system.
Vertically, the structure’s circular plan changes radius, beginning at the first twenty-two levels
which feature floors of progressively smaller radius after which there is a transition to an
inverted conic shape, whereby the floors increase in radius up the remainder of the structure. The
perimeter column system creates sleek vertical lines down the building, accentuating the
hourglass silhouette of the structure. Kasturi once again uses the stepped roof canopies at the
structure’s entrance to resonate the traditional Malay housing.
II. Hong Kong, Peoples Republic of China (3 days)
The design of tall buildings in Hong Kong represents the ultimate challenge from the perspective
of structural engineering, with earthquake and typhoon loads that far surpass the levels
anticipated in any American city. While earthquakes pose challenges on the west coast and
hurricanes on the east coast of the US, no major city bears the brunt of both of these natural
hazards as Hong Kong does. In particular, the significance of wind loading in this area
necessitates efficient choices of structural systems and aerodynamic forms to achieve satisfactory
performance under the action of wind. The structures featured in this visit have been able to
combine architectural, structural, and aerodynamic considerations to meet the extreme natural
loads in this region, while incorporating important cultural themes. A three-day study of the
landmark structures, which utilize their unique structural systems to define distinctive
silhouettes, will include Two Pacific Place/Island Shangri-La Hotel, the Hopewell Center,
Citibank Plaza, The Centre, and specifically the following projects:
• Hong Kong & Shanghai Bank
Sir Norman Foster’s first experience in skyscrapers was completed in 1986. The suspension of
individual stories from the perimeter steel load-bearing frame permits open views from end to
end and creates office spaces flooded by natural light. The structural system is actually a hybrid
comprised of a mast system linked at five levels by trusses to form a five-level unbraced sway
frame. In this respect, the project serves as unique use of structural components to achieve a
desired architectural effect.
• Central Plaza
Standing at the mouth of the harbor, Central Plaza was designed with a perimeter tube and core
system to resist typhoon winds. In order to satisfy occupant comfort criteria, this slender building
underwent extensive wind tunnel testing. Its triangular floor plan with notched corners embodies
the type of aerodynamic modifications that can yield successful designs, particularly from the
perspective of reducing crosswind response. Interestingly the notching of the corners also echoes
Chinese etiquette, as directing pointed corners at neighbor may be considered offensive, marking
the interplay between cultural ethics and aerodynamic form. The intricate cladding of gold and
silver with ceramic, painted patterned glass yields a finish that truly shimmers in the sunlight,
with the Central Plaza serving as a beacon at the foot of Hong Kong harbor.
• Bank of China
I.M. Pei created arguably the most famous building in China with the design of this seventystory tower, currently eighth tallest in the world. The premise for the building is based upon the
Chinese symbol of the bamboo shoot, an image of growth. The use of the trussed tube system, a
highly efficient modification to the framed tube that engages the exterior columns to resist lateral
shear by axial forces rather than flexure, permitted the trademark prismatic profile of the
structure. In some respects, the termination of distinct tubes in the structure with height echoes
the famous bundled tube features of the Sears Tower. This choice of structural system permits
more clear space than traditional tube systems, and the triangular slopped roofs, which result
from the termination of tubes at different levels of the building, provide elegant skylights. The
choice of glass and aluminum cladding creates a transparent effect, reflecting the surrounding
greenery of the hillsides and the clear, blue Chinese sky. This, coupled with its unique prismatic
shape, makes the Bank of China a glimmering jewel in the Hong Kong Skyline.
• Hong Kong Convention and Exhibition Center
Though not a skyscraper, this structure is truly a signature piece on the Port of Hong Kong,
marking the location of the landmark transfer of rule from Britain back to China. This facility is
nothing short of a structural engineering feat, considering the intricate truss work necessitated to
create the smooth curves and contours of the roof system. Its symbolism as a bird prepared to
take flight out over the sea embodies bustling growth and innovation, while its shimmering
cladding rings with the modernism that is today’s Hong Kong.
III. Shanghai, Peoples Republic of China (2 days)
The Lujiazui Central Financial district is quickly growing with the immergence of several tall
buildings, framed by the Huangpu River. Although development of this area is still underway, it
will serve as one of the most important international financial centers with several major banks
having erected impressive testaments to their financial growth here, defining this region as the
“Wall Street of China.” Shanghai, in its present form, offers an opportunity to observe the
development and construction of several major projects, as well as many impressive projects
recently completed, including Nanjing Xi Lu, Oriental Pearl Tower, Yin Du Building, China
Merchants Tower and the Shanghai Securities Exchange. Particular projects of interest
include:
• Jin Mao Building
Utilizing a reinforced concrete core for resistance to typhoons and earthquakes, the Skidmore,
Owings, and Merrill project stands as the tallest building in China and fourth tallest in the world.
The façade of the structure is intended to echo the design of the Art Deco quarter of the Old
Shanghai, located in the Pudong district. The use of setbacks and a gradual tapering with height,
while beneficial from the perspectives of reducing wind effects on the structure, echoes the
tradition of the Chinese pagoda, once again carefully integrating traditional culture into modern
skyscraper design. The golden light cast from the building in the sunlight helps to reiterate the
significance of its name – Jin Mao or “Much Gold.” Care was also taken to include, in its design,
multiples of eight, as the number eight holds special significance in Chinese culture.
• Shanghai World Financial Building
Although temporarily delayed, the construction of this proposed world’s tallest building is
underway. When completed, the structure will feature a shaved face with a complete throughbuilding opening that, while adding a distinctive signature to the building, actually helps to
relieve wind pressure at this location. Though it is not complete, from the perspective of a
structural engineer, the construction of any project of this proportion is, in itself, a tremendous
learning opportunity.
In total, the trip will spend 9 days in Asia, allowing one day for travel between each location.