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July 11 – 15, 2005 Gdańsk, Poland
University of Beira Interior, Covilha, Portugal
1. Introduction
Tall building, as an element of urban environment is rapidly gaining the importance.
It is more and more the dominant element of the city skyline and often becomes even
the symbol of the city. Also the impact of the tall building on the city is enormous. It
influences the environment of the whole neighbourhood in many aspects from problems
connected with transport till such small aspects as shadows. Therefore planning and
design of tall building in city environment is an interdisciplinary problem, which has to
be dealt with be a teams of specialists from various specializations.
2. Council on Tall Buildings and Urban Habitat
• The Council on Tall Buildings and Urban Habitat, is an international non-profit
organisation, which task is to facilitate professional exchanges among those
involved in all aspects of the planning, design, construction and operation of tall
buildings and the urban habitat.
• The Council's primary goal is to promote better urban environments by maximising
the international interaction of professionals, and by making the latest knowledge
available to its members and to the public at large in useful form.
• The Council has a major concern with the role of tall buildings in the urban
environment and their impact thereon. Providing adequate space for life and work
involves not only technological factors, but social and cultural aspects as well.
• While not an advocate for tall buildings per se, in those situations in which they are
appropriate, the Council seeks to encourage the use of the latest knowledge in their
2.1. Council Authorities:
The Steering Group is the "Board" of the Council. An Executive Committee carries
out the policy of the Steering Group. Council Headquarters is located at: Illinois
Institute of Technology. S.R. Crown Hall, 3360 S. State Street. Chicago, Illinois 60616
USA,, [email protected] Correspondence: Geri Kerry, Council on Tall
Buildings and Urban Habitat, PO Box 4363Bethlehem, PA. USA 18018 email
[email protected]
Ron Klemencic, Skilling Ward Magnusson Barkshire, Seatle, USA.
Executive Director
David M. Maola
Director Emeritus
Lynn S. Beedle
Vice Chairmen:
• Africa: Syd Parsons
• Australia: Henry J. Cowan Ph.D
• Europa: Ryszard Kowalczyk, Ph.D
• Middle East: Sabah Al Rayes Ph.D
• North America: Joseph P. Colaco, Ph.D
• Northern Asia: Prof. Fu-Dong Dai
• South America: Edison Musa
• Southern Asia: Kenneth Yeang, Ph.D
• Vice Chairman at Large: M. Ridzuan Salleh Ph.D
2.2. Need:
• the growing world population, generally urban, creating increase
• demand for tall buildings in areas experiencing urban growth
• the consequent requirement for economy in construction
• the frequent neglected of human factors in urban design at the
• expense of livability and the quality of life
• the need to revitalize urban areas experiencing decline through
• poverty or crime
• the new research required in the field and the necessity of
• establishing priorities
2.3. Activities:
• Publications
• Conferences and Congresses
• Database and Information Resources
• Identification and Implementation of needed research
3. Tall building - definition
Perhaps the first question, which should be answered, is the definition, what is
considered to be a tall building. Council on Tall Buildings and Urban Habitat dives
following definition of tall building: “A tall building is not defined by its height or
number of stories. The important criterion is whether or not some aspects of “tallness”
influence the design. It is a building in which tallness strongly influences planning,
design, construction and use. It is a building, whose height creates conditions different
from those that exist in “common” buildings of a certain region and period. Lest me
explain this in a manner Dr Beedle, the founder of the Council and my friend has
explained this. If the fire brigade comes to extinguish a fire in a building and its
equipment is not sufficient to reach some floors it means that for the fire brigade this
building is considered tall. If in a town where there are only buildings let say two three
floors high suddenly a building is built with twelve stories and it looks tall therefore it
is considered as a tall. The definition is therefore relative, and depends from the aspects
taken into consideration. Talking about Civil Engineering aspects the building can be
considered as tall when the structural systems depend on tallness, that commonly means
that horizontal forces decide on structural system of the building.
• Tallness makes that many problems, which can be disregarded in “common
buildings” in tall buildings appear as very important ones which must be solved to
achieve a proper solution.
• Thornton [ “How Tall” Engineering News Record 1983]:
“I think everybody has the question do we really want 200-story buildings? I’m not sure
we do. I’m sure that engineers and architects could produce one and the construction
industry in the US could produce it with no problem. But the interesting thing about
working on 200-story building or long span structures is that you learn a lot about
exaggerated magnitudes of behavior. When you are working on 20, 30 or 40-story
building, there have been 100 of these built before. When you start talking about 200,
400, 500 - story buildings, everything gets exaggerated - differential column shortening,
drift, acceleration, dynamic behavior and as we study them in a tall building, we
wonder, why we didn’t think about them on a shorter building”.
• Present tall building is a result of close co-operation of a team of specialists of
various areas and only, if this co-operation is close from the very beginning a
successful solution is possible.
• Structural system and vertical transportation were usually the main factors limiting
the height of a building
• Taking into account present developments in technology, these two factors
constitute no real limitation to the height nowadays.
Fig. 1. One Mile Dream
4. Tall building and its role and function
Although tall buildings are generally considered to be a product of the modern
industrialized world, inherent human desire to build skyward is nearly as old as human
civilization. It is recorded in the Bible in the story of the Tower of Babel “and they said:
go to, let us built a city and a tower whose top may reach onto heaven”. The builders
thought, that they could reach heaven with their construction and their audacity was
punished by God. This tale expresses clearly one of human aspirations: to reach heaven
by the extreme height of the structures, to reach sky and go far above our earthly realm
to a place that is higher, purer, with not obstructed view around.
The Egyptians started to built pyramids some 5000 years ago, and ziggurats in
Mesopotamia are almost as old. Also Mayan pyramids, Egyptians obelisks, Chinese
pagodas and Moslem minarets thought are not as tall but they create an vertical element
so much taller than anything around, a vertical marker against the horizon. Steeples of
churches in the Christian tradition, campaniles have played a similar role. This is
another attribute of very tall structures that they are place markers. Very tall structures
do not only mark a place, but they often become the symbol of a place as for instance
Eiffel Tower in Paris.
In the 20th century office buildings have become the dominant, tall objects in our
cities, representing often private wealthy corporations or individuals. Perhaps it is
difficult to accept the fact that those buildings have replaced traditional sacred or civic
structures as the symbols for new cities. The earliest skyscrapers were received by
public with great enthusiasm. Now in several places they have become too many, often
some of them being insensitive to their cities and environment or less than beautiful and
they provoked a well justified negative reaction. But in many places they continue to be
built with great enthusiasm, most notably in eastern Asia. They continue to be a great
architectural and structural undertaking which appears simple at the surface, but is
surprisingly difficult to be solved well.
The Council book “Architectural Design of Tall Buildings” [1] says following: “Tall
building should respond to the two primary criteria: first to the smaller circle of its
affected users and second to the larger urban environment. In regard to the first
criterion, the building itself must be ganged relative to its purpose, how its lives up to
its expectations. The second criterion must be evaluated in its functions an element in
the immediate urban setting. The degree to which tall buildings add or detract from the
quality of their surroundings is dramatic, affecting not only the immediate users but,
because of their size and scale the context of the entire city now and in the future”.
Ceasar Pelli the famous architect and designer of several tall buildings in his paper
“Cosmic Pillars” [2] makes following important comment: “A new skyscraper is a
member of an important class of buildings with well defined characteristics. It belongs
also to the place where it is built. It needs to respond in a creative and responsible
manner to the climate, surrounding buildings, architectural tradition and to the
character, history and ideas of the city and its people. Only than it will be noble and
worthy of respect and affection”. These are general principles which have to be taken
into consideration whenever a tall building is planned for the city. Unfortunately not
always was so.
5. Large Cities Around the World and Tall Buildings
Stating that the tall building is a significant element of the urban environment lets us
look at the different parts of the world and evaluate the tendencies for tall buildings.
In Europe there is some growing tendency to construct tall buildings in cities, but
with some limitation of the height, without any race for the records. Most of the tall
buildings are designed for large companies or banks. The reasons for building tall is to
accommodate in one building the offices of the company, to have some office space for
renting, which in some cities is still a good business, and utilize in most effective way
the urban space which is very expensive.
In the USA the tall building in great towns is just a common thing. The main reason
for going tall is high price of the lot in the city. In some cases there is still a desire for
regaining the world record in tallness.
Asia presently seems to be the spot, where tall building are considered as one of the
solutions to the rapidly growing population. Most of the very high buildings presently
designed aiming at the world records in height are situated in Asia.
Australia: No shortage of space in the country. However in cities many tall
buildings emphasising importance and prestige of large banks, enterprises, hotels.
Mixture of tall and small buildings in big towns
Central and South America: Tall buildings in cities of big towns. Prestigious
companies, banks, hotels, offices are often located in cities in tall buildings
Africa: Tall Buildings in some capital cities. Relatively many t.b. in cities of South
Africa such as Johannesburg, Cape Town, Durban. Egypt, Cairo also several t.b. All of
moderate height.
Middle East: Many new T.B. particularly in Emirates. Interesting architectural
expression. Many of them very expensive. A survey of various Cities and their skyline
and tall buildings (many slides)
6. Development of Structural Systems.
6.1. Structural Systems and Outside Envelope
• The outside image, the architecture, is the first expression of tall building and
usually T.B. can be recognised by its characteristic shape and its architectural
expression. (First Part was showing many images of T.B. around the world).
• However for structural engineer, most significant in each building is the structure,
which very often is covered under the skin of the building, under its outside
• It is the structure, which similarly to the spine of human body, holds upright the
building, carries on all acting loading and makes possible the building erection and
• Not very often a building exposes its structure, as for instance the John Hancock
Centre or the Onterie Centre in Chicago.
• In the majority of buildings the structure is not exposed. It is located inside the
building and covered by outside envelope.
• This fact was one of the reasons that the Council on Tall Buildings and Urban
Habitat devoted one of the Monograph volumes to reveal the structural skeleton, to
demonstrate its role in carrying loads and to describe the evolution and development
of structural systems.
• The book: “Structural Systems for Tall Buildings” is a main source of materials for
this presentation.
• The source of presented figures is either CTBUH slide collection or Internet:
6.2. Historical Development of Structural Systems
The history of modern Tall Buildings starts in the US in Chicago in the end of
nineteenth century after the great 1871 fire, which devastated the city. It is generally
acknowledged that the first skyscraper was built in Chicago in 1885 and it was a Home
Insurance Building. This building was designed by William le Baron Jenney as 55
meters high building, which unlike traditional buildings in which the exterior walls
were self-supporting solid masonry, the structure of this building consisted of skeleton
of iron or steel frames, which carried the vertical and horizontal loads to the
foundations. This was a completely new structural solution. The building became a first
logo for the Council on Tall Building and Urban Habitat.
The rapid development of tall buildings in the beginning of twentieth century was
parallel with the development of building materials of better quality such as steel and
later on concrete and combination of basic structural systems such as bearing (shear)
wall, frame and truss.
6.3. Effects of Tallness on Structural Systems
With increasing height of the building, the influence of horizontal loads governs the
selection of structural system. The major concern of the designer is to select a system
strong enough to take over all loads and actions, stiff enough to keep deformations
(drift) in prescribed limits and still economically sound. Of course there is some
premium which has to be paid for height, but the goal of selection of appropriate
structure is to keep this premium at the possible lowest level.
6.4. Basic Structural Systems and their Combinations
In general the structural systems for tall buildings are composed of purposely
selected combination of one or several of the following basic systems:
• shear wall load bearing wall)
• frame (braced frame, moment resisting frame)
• truss (braced frame, outrigger)
6.4.1. Braced Frame and Moment Resisting Frame
• This fundamental lateral force resisting system evolved during the beginning of
high-rise construction in the early twentieth of this century.
• Frames are normally arranged as planar assemblies in orthogonal directions to create
planar frames or tube frame systems.
• The two systems may be used together as an overall interactive system and are used
today as effective structural system in buildings up to 40 - 50 stories.
6.4.2. Shear Wall Systems
• Shear walls have been the most common structural systems used in the past for
stabilising building against horizontal forces.
• With application of reinforced concrete, shear wall systems have been used widely
even to stabilise the tallest building structures.
• Introduction of high strength concrete expanded even more the possibilities of
resisting horizontal loads by shear wall systems.
• Usually, a shear wall system for tall building groups shear walls around service
cores, elevator shafts and stairwells and forms a stiff box-type structure. (internal
• Multiple shear walls throughout a tall building may be coupled to increase overall
building stiffness
• Shear walls in form of closed boxes provide also efficient solution against torsion.
6.4.3. Frame Truss Interacting Systems:
• Shear trusses combined with moment resisting frames produce a frame-truss
interacting system.
• The linear wind sway of the moment frame - combined with cantilever parabolic
sway of the truss - gives the system increased lateral stiffness.
• Often core trusses are combined with moment frames, which are located on the
perimeter of the building.
• Optimum efficiency is achieved, when columns designed for gravity loads are used
as truss chords, without increasing their dimensions for wind forces.
• These are than combined with gravity designed exterior columns and spandrel
beams with rigid connections. If for such combination the lateral stiffness is
adequate - the solution would provide an optimal design.
6.4.4. Core and Outrigger Systems:
For modern high-rise buildings frequently chosen system is central elevator core
combined with perimeter frame, which gives the possibility to arrange large column
free floor space between the core and the exterior support columns. This solution allows
greater functional efficiency, but also effectively disconnects the two major structural
elements: core and columns, available to resist the critical overturning forces present in
high- rise building.
The incorporation of outriggers couples these two components - shear core and
support columns on the perimeter of the building and increases very significantly the
system ability to resist overturning forces. (example City Spire N.Y.C 75 stories, 248m
high; City Bank Plaza, Hong Kong, 41 stories, 220m high)
Typical structural systems used in steel and concrete tall buildings of moderate
height were:
• Shear wall systems
• Frame - shear wall interacting systems (internal core, frame on the periphery)
• Core, frame, outriggers
Fig.2. Structural Systems
6.5. Tubular Systems
FAZLUR KHAN - Milestone in the evolution of tall building systems: Development
of the equivalent cantilever tubular system.
All previous improvements in structural systems contributed to extend the range of
applications of frame-type behaviour, the radical departure occurred only when the
structure was placed on the perimeter and was so interconnected to act like three
dimensional cantilever utilising the entire exterior form.
The characteristic of this exterior structure was that of wall, giving rise to the
terminology “tubular structure” to designate silo-like cantilever behavior of this
With this innovation the structure had emerged from the interior to the exterior,
thereby significantly impacting the architectural expression of the façade and shaping of
the overall form. The best example of efficiently applied in steel of a tube structure is
John Hancock Building in Chicago.
The Trussed Tube:
The trussed tube is a solution which uniquely suits the qualities of structural steel
and was first applied for this material.
The ideal tubular system is one which interconnects all exterior columns to form a
rigid box, which can resist lateral shear by axial forces in its members rather than
trough flexure. This can be achieved by introducing a minimum number of diagonals on
each façade and arranging these diagonals in such a way, that they intersect at the same
points at the corner columns.
The behavior of framed tubes under lateral load is indicated on the next figure (Fig.
5.), which shows the distribution of axial forces in the exterior columns.
Fig.3. Layout of the building in frame structure and tube structure
Fig. 4. Tubular Systems: a. Frame/brace with belt truss, b. Framed tube,
c. Diagonally braced tube, d. Framed bundled tube,
e. Diagonally braced tube without internal columns,
f. Diagonally braced tube without internal columns,
g. Space truss, h. Interior diagonally braced frame
Fig. 5. Framed tube behavior
The more the distribution is similar to that of a fully rigid box cantilevered at the
base, the more efficient the system will be. For the case of a solid wall tube, the
distribution of axial forces would be expected to be uniform over the windward and
leeward walls and linear over the sidewalls.
As the tubular walls are punched creating beam-column frame, shear frame
deformations are introduced due to shear and flexure in the tubular members as well as
rotations of the member joints. This reduces the effective stiffness of the system as a
cantilever. The extend to which the actual axial load distribution in the tube columns
departs from the ideal is termed the “shear lag effect”.
In behavioral terms, the forces in the columns toward the middle of the flange
frames lag behind those nearer the corner and are thus less than fully utilised. Limiting
the shear lag effect is essential for optimal development of the tubular system. A
reasonable objective is to strive toward at least 75% efficiency such that the cantilever
component in the overall system deflection under wind load dominates.
The idea of tube structures so efficiently applied in steel for John Hancock Building
was also applied by Khan for his concrete buildings for instance One Shell Plaza
building in Huston and others, in which framed tube structure was placed on the
perimeter of the building.
The framed tube system consists of the arrangement of closely spaced exterior
columns and deep spandrel beams rigidly connected together, with entire assemblage,
continuous along each façade and around building corners.
The system is a logical extension of the moment resisting frame, whereby the beam
and column stiffness are increased dramatically by reducing the clear span dimensions
and increasing the member depth. The monolithic nature of reinforced concrete is
ideally suited for such a system, involving fully continuous interconnections of the
frame members.
This solution was also applied in steel, when for framed tube welded beam-column
connections were utilised to develop rigidity and continuity of joints. (Examples:
concrete - One Shell Plaza 218m high, steel - World Trade Centre 417 m high)
Tube in Tube systems and bundled tube systems
The development of the interior core system as a wall tube, was applied in many
buildings. Arrangement the interior core together with exterior one in a form a framed
tube, braced tube offered opportunities for larger stiffness and therefore possibilities for
greater heights. Such systems are called TUBE IN TUBE. Many systems shown before
were just tube in tube systems.
Fig. 6. Tube in tube and Bundled tube
Other structural solution: spatial arrangement of tubes - bundled tube system is
also credited to Fazlur Khan. This concept was born from the requirement of vertical
planning modulation and shear lag for very tall buildings. It allows to arrange wider
column spacing in the tubular walls, than would be possible with only the exterior
frame tube form, and this is advantage for interior space planning.
In general any closed form shape can be used to create the bundled form. SEARS
TOWER (Fig. 7) is an example of bundled tube structure.
Fig. 7. Sears Tower - example of bundled tube
The Trussed Tube concept was first applied by F. Khan for steel in John Hancock
building in Chicago already in 1965 year (starting of erection of the building).
The trussed tube concept can also be applied to reinforced concrete construction by
arranging diagonals in the facades of the building.
A diagonal pattern of windows perforation in an otherwise framed tube is filled in
between adjacent columns and girders (Onterie Center, Chicago, 171m high).
The principle of façade diagonalization can also be used for partial tubular concepts
for instance using diagonalized frames only in the corners of the building.
6.6.Hybrid Systems
Tall building have been traditionally designed to make use of a single type of lateral
load resisting system - initially simple moment resisting frames and than shear wall
systems and framed tubes.
Until the advent of economical, easy to use, high capacity computer hardware and
software, structural systems had to be amenable to hand calculations or computer
analysis using limited capacity machines. Nowadays computer capacity is not a issue,
and decisions on structural systems are made on the basis of their effects on the
appearance and functioning of the building and its constructability. This is not to
suggest that anything is acceptable - the engineer must still be aware of the pitfalls of
creating abrupt discontinuities in building stiffness, the long-term effects of differential
axial shortening and other side effects of using mixed systems and multiple materials.
Example: Overseas Union Bank Center in Singapore: braced steel frame was used
because it lightness, long spanning abilities, small member sizes, absence of creep
shortening, and, combined with concrete shear walls, for its very cost-efficient
contribution to lateral stiffness.
Another type of a hybrid system gaining popularity is the concrete-filled steel tube
column, where the erectability of a steel frame is maintained, but the cost-effective axial
load capacity of high strength concrete is used. Of course fire protection must be
considered. If the steel tube is considered as sacrificial in a fire, than internal
reinforcement must be sufficient. If concrete can be pumped into the column from the
base of each pour, than a number of stories can be concreted at one time and vibration
of the concrete is not necessary (Two Union Square, Seattle).
The trends of modern architecture sometimes force the structural engineer away
from convention in a search for a structure that will accommodate aesthetic and
functional demands while meeting structural requirements. The result may be a
structure, which on one face of the building is of a different type than the other faces.
First Bank Place, Minneapolis, is a structure with a number of quite different
elements forming its lateral load resisting frame. A braced steel core is connected via
outrigger beams to large high strength concrete perimeter columns, incorporating castin steelwork to aid erection and connection. Although this system provides in-plane
stiffness, its lack of torsional stiffness required that additional measures be taken, which
resulted in one bay of vertical exterior bracing and a number of levels of perimeter
Vierendel “bandages”. Perhaps this solution can be a good example of structural art.
With the advent of high-strength concrete (above 50MPa) has come the era of the
“supercolumn” where the stiffness and damping capabilities of large concrete elements
are combined with the lightness and constructability of steel frames. High strength
concrete when includes silica fume and a high-range water reducer, exhibits
significantly lower creep and shrinkage and is therefore more readily accommodated in
a hybrid frame.
The Interfirst Plaza in Dallas uses supercolumns in conjunction with an almost
conventional steel frame.
Columbia Seafirst Centre in Seattle incorporates very large super columns
connected by steel diagonal members to a braced steel core Examples: in the book
“Structural Systems for Tall Building’s
The examples suggest that hybrid structures are likely to be the rule rather than the
exception for future tall buildings, whether to create acceptable dynamic characteristics
or accommodate the complex shapes demanded by modern architecture. Hybrid
structures are not something to be tackled by the novice engineer armed with a powerful
microcomputer and a structural analysis software package. A sound knowledge and
understanding of material behavior (such as ductility, damping, creep and shrinkage)
which is not included in analysis and design packages and mostly not codified is
essential and constructability must be a parallel consideration.
However, without hybrid structural systems many of our modern tall buildings may
never have been built in their present form.
7. Trends for the Future
7.1 Basic Aspects
Designing of a tall building is a complicated process in which many, some times
controversial, requirements are to be solved and compromised. The tall building is
therefore a work of team of architects, structural engineers, mechanical and electrical
engineers and many others working together from the very beginning of the design
process and the solution and economy of structure as well as fulfilling the expectations
of users depends on the good cooperation of designing team. It is difficult to predict
what kind of structural systems will be used in the nearest future as this depends
strongly on the development of technology, new materials, new computational
For Tall Buildings for the future the following aspects are to be taken into
consideration in selection of material and structural system:
• It seems that there will be greater emphasis on quality.
• Computer will become ever more significant. It can be a basis for powerful
knowledge-based planning, design and operation of facilities. Computer assisted
design allows to examine a variety of designs and variety of sophisticated solutions
and makes easier the selection of the optimal one for given requirements.
The structure of the building cannot be considered alone. In the future buildings
more attention will be devoted to integrating structure with service system and
architectural requirements. Under service system we understand vertical transportation,
HVAC, plumbing, electrical systems, fire protection, environmental systems and
security. It is worthwhile to mention that the cost of building service systems in a
modern high rise building can be over one-third of the building total first cost, and over
two-thirds of its 25-year total life cycle cost.
The energy conservation is a major concern and is reflected in the best designs
available throughout the world. Good effects could be achieved by integration of above
mentioned systems monitored and coordinated by computers. More and more buildings
are considered as “intelligent buildings” in which high-technology, intelligent
integrated systems are applied in the building.
• More attention is devoted to develop a better façade of the building. Modern façade
should have the ability of storing and channeling the energy therefore contribute
more efficiently to the energy balance of the building.
• More attention is to be given in design to the interaction of building structural
systems and non structural components – like partitions and claddings. The
lateral load-resisting structural system of a tall building and the non structural
components of the building interact with each other in two basic ways, that are of
practical significance. Firstly deformations of the structural system due to lateral
loads can introduce distortion and possibly damage in the non-structural elements.
And secondly, the stiffness and energy absorption capacity of the non-structural
elements can affect the response of the structure to loading.
Besides the above mentioned aspects, from the analysis of the recent projects, both
already erected and others not built yet, some general trends can be derived for the
nearest future, which can affect the selection of structural systems:
• broad use of composite structures
• broad application of high-strength (HSC/HPC) concrete particularly for super• columns. (Examples: Increased height of concrete buildings recently erected 1960:
Lake Point Towers - 164m, 1976- Water Tower Plaza- 262), 1990: 311 South
Wacker Drive - 292m, 1992: Central Plaza H.K. – 374m, 1998: Petronas Towers 472m
• application of outrigger systems to assure better interaction of internal core and
perimeter structure, broad application of tube systems
• use of active and passive damping systems
• use of better analytical tools and testing facilities (i.e. wind tunnels)
• use of mixed systems and mega-structures
After September 11, 2001 terrorist attack some new recommendations were
elaborated in order to increase the safety in tall buildings and possibilities of
The race for building the “world tallest” does not stop and moved rather to Far East.
Seven of the world’s tallest buildings were completed in the late ‘90s; eight of the top
10 are in Asia. Kuala Lumpur has passed the crown to Taipei in the end of 2004, and
Taipei, is likely to Shanghai or other city later this decade. Hong Kong, Seoul and
Tokyo are also in the race as well as Dubai.
7.2. How Tall ?
The question “how tall” will be the buildings in the nearest future perhaps needs
some consideration. With present technological developments buildings of the range of
200 stories and higher seem possible from structural and vertical transportation point of
view. The other question is whether we need such a tall buildings for our cities and
whether the solution will be economically sound.
The race for building the “world tallest” did not stop and moved rather to Far East.
Seven of the world’s tallest buildings were completed in the late ‘90s; eight of the top
10 are in Asia. Kuala Lumpur has passed the crown to Taipei in the end of 2004, and
Taipei, is likely to Shanghai or other city later this decade. Hong Kong, Seoul and
Tokyo are also in the race as well as Dubai.
Why the race? Ron Gluckman in his paper: “How high will they build? [Popular
Science, March 2003] says: “To be blunt, in Asia today, as in New York 70 years ago,
nothing is more demonstrative than a huge, well, upright symbol. Rival nations and
corporations work overtime to show they are high-tech powerhouses.“ Height as a
manifestation of technology, is tied up with cultural aspirations” says Eric Howler, an
architect with KPF, which is designing Union Square, a 108-story building that will,
Howler says, be the world’s tallest when completed in 2007.”
In China KPF-designed Shanghai World Financial Center has restarted with
redesign that will top Taipei 101. Kohn says “but I guarantee it will be the tallest”.
SOM has started with the Burj project for Dubai which is planned to be 705m high.
There are also plans for a building in Seoul of the range above 530m.
This competition may raise the question: haw tall can buildings go? Craig Gibbons
[Popular Science, March 2003] director of the Hong Kong office of Arup, a global
structural engineering firm “we could build a kilometre-tall building right now, no
question about it. Two hundred, even 300 stories tall, is possible because we can take
advantage of lighter, high strength materials”.
The problem which Gibbson sees is “we’d need an advance in lift technology and in
cranes” .
Ron Klemencic says: “The limitations are more financial and practical, how to move
people up and down those great heights. Above 80 stories, the area you need to devote
to vertical lift, like elevators, versus rentable space, just is not viable.”
This however again is not a problem: Advances in material and elevators make tall
buildings more efficient. In Shanghai Jin Mao building are used high speed elevators
(9m/sec). There are double deck elevators, and recently Twin elevators were introduced
by Thyssen Krupp allowing operation of two cars in one shaft. This considerably
reduces the demand for elevator space in the building.
Efficient dumping devices became a common solution reducing dramatically
movement of buildings caused by typhoons and earthquakes. “Taipei 101 will feature
the world’s largest passive tuned mass damper, an 660-ton sphere around 5,5m in
diameter which will swing like a pendulum from 92nd floor in the view of restaurantgoers”.
New Code regulations were introduced in some Asian countries even before
September 11:
• Composite structures are commonly used for tall buildings - this solution gives more
fire resistance
• Every 25 floors Hong Kong building must have a refugee floor-- empty and
designed to resist smoke accumulation. Many stairwells are pressurized.
• Atrium size is restricted
• Water tanks on the roofs of tall buildings are sometimes engineered to let the water
slosh about, doing double duty as wind dampers
• Dedicated firemen’s lifts are required in many Asian countries “In Hong Kong they
are required to reach any floor in the building in an extremely short period of time,
so they are profiled like a bullet to avoid drag, and travel as fast as 9m/s.
“The idea of super-tall towers, vastly higher than anything now built, has long
fascinated architects and urban planners. In 1956 Frank Lloyd Wright…. designed the
Illinois Tower, a mile high, 528 stories in all….. It was technically feasible, he said ,
but for the elevator problem.”
Later were many proposals as for instance Tokyo Sky City 1000m high, Sir Norman
Foster sketches for Millennium Towers in Tokyo and Shanghai both around 800 m.
Mir M.Ali architecture professor at the University of Illinois asks: “But who wants
live in a building 1 mile high?” A more realistic height for the 21 century, he believes is
around 150 stories and 600m.
Architects like Pelli have already designed such towers. Likewise SOM’s and
KPF’s. “Humanity has an obsession with building big” says Pelli, whose Two
International Finance Center will soon become Hong Kong’s tallest tower. “ Part of it is
the human element. That’s why a tall TV tower isn’t so important. When we see
humans in a building, and know there are eyes up there, that’s emotional connection.
Tall has power”
8. Examples of Application of New Structural Solutions
8.1. Existing Buildings:
8.1.1. Petronas Towers, Kuala Lumpur
Record height holder till 2004 - Petronas Towers (452m) in Kuala Lumpur Malaysia
are twin buildings equivalent to 95 stories in height. Composite construction was an
important part of their design from early in the project, to provide long span open
floors, fast erection and future adaptability. The structural system consists of the core,
and sixteen ring columns, which are connected by a haunched ring beam on each level.
Lateral loads are shared by the columns and the structural concrete core trough floor
diaphragms. Floor construction consists of composite metal decking and steel infill
beams. Concrete outrigger beams, which link the core and perimeter at levels 38 and 40
round out the composite system.
8.1.2. Bank of China Building, Hong Kong
In time of its erection (1989) Bank of China building in Hong Kong was a major tall
structure outside the United States (368m) in which economy and elegance go together.
Thanks close co-operation of architect I.M.Pei and structural engineer Leslie Robertson
both designers came up with unique form which provides both the structural and
esthetic elegance of the tower and the economy of structural solution. The idea of
diagonal bracing as in John Hancock Center and the cut-off tube idea of the Sears
Tower were brought together in a original way. For the first time a pure space-truss was
used to support almost the entire weight of the building while making use of the same
system to resist lateral thrust of the wind (wind loads in Hong Kong are twice those
required in New York and these wind loads are four times larger than the earthquake
forces that would be required in Los Angeles).
The structure of the tower is a square tube made up of eight vertical plane frames,
four of which comprise diagonal bracing. All of the building’s loads are collected and
transferred through frames to four massive composite steel corner columns. A fifth
column extends through the center of the tower from the top to the 25-th floor, where it
transfers the accumulated loads diagonally to the four corner columns. By sending
gravity loads to the extreme corners of the building, resistance to high wind forces is
increased and the building interior remains column free.
8.1.3. Plaza Rakyat, Kuala Lumpur
The construction of the 77 story, 382 m. high, Plaza Rakyat building in Kuala
Lumpur is on hold. Expected construction end is 2006. Building was designed by
Skidmore Owings & Merrill office in Chicago and belongs to one of the tallest
reinforced concrete building in the world and also one of the most slender with an
overall aspect ratio of over 8 to 1. The innovative solution belt wall/core interacting
system was introduced, which is applicable to very tall buildings in low to moderate
wind climates and to buildings in the mid-height range in moderate to high wind
climates. The lateral load resisting system components are the concrete core walls and
coupling beams, the exterior beam/column frame, and the two story belt and outrigger
walls located at levels 28, 51 and 73.
8.1.4. Jin Mao Tower, Shanghai, China
The composite structural system for the 88-story, 421m high building in Shanghai
was designed by the Skidmore, Owings & Merrill office to resist typhoon winds,
earthquake forces and accommodate poor soil conditions, while providing a very
slender tower to be fully occupied for office and hotel uses. The building is the tallest
building in China. The superstructure of the tower resisting lateral loads is composed of
a octagonal central reinforced concrete shear wall core interconnected with eight
composite mega-columns through composite outrigger trusses two story high located on
levels: 24, 51 and 85. The foundation system for the Tower consists of open steel pipe
piles capped by a reinforced concrete mat.
Many systems of the building are monitored and integrated by computer. The
building is considered as one of examples of “intelligent buildings”.
8.1.5. Burj Al Arab, Dubai
The ultramodern hotel, shaped like traditional sailboat was shortly opened in Dubai.
This hotel with its 321m heights is the world’s tallest hotel. The building was built on
the artificial island linked by bridge to Dubai and is characterized by a dramatic
structural steel exoskeleton and a soaring 200 m tall atrium, shielded from outside view
by a sail shaped, 50 m wide stretched-fabric wall. Atkins Company was responsible for
total design, construction management and procurement of everything.
In its V-shaped footprint, the tower’s two roughly 90-m-long, 15 –m-wide guest
accommodation wings, made of concrete walls and slabs, spread from a service core.
Wing walls and the core transmit vertical loads down to the pile foundation. Wind and
earthquake resistance in one direction is provided by the highly visible exoskeleton
acting compositely with the core.
The exoskeleton is a pair of steel trusses rising 273 m above ground. Each
aluminum-clad truss stands upright, like an archer’s bow, with the vertical element built
compositely with the core. The curved legs stand, only lightly connected to the wings,
about 12 m outside the curtain walls. The generally 1,8 x 4,5 m uprights of each bow
are braced together with horizontal and diagonal elements.
Wind stability in the other direction is from a stack of three structural steel crosses,
bracing and connecting the open ends of the guest-room wings to close the V plan, and
sharing loads with core. The bracing, about 50 m across, is hidden behind a two-layered
wall of translucent glass fiber fabric, coated with polytetrafluoroethylene. To form a
atrium’s 50 m wide, 200 m tall outwardly curved wall, fabric is stretched over a ladder
of bowed, horizontal trusses between ends of the wings.
Easier ways to stabilize the tower were certainly available but the plan by Atkins´
project architect Tom Wills-Wright had the winning aesthetic appeal.
The building is designed for a 50-year wind of 45m per second and 0,2g seismic
ground acceleration. Two tuned mass dampers, weighting about 2 tones each limit
vibrations in the tubular steel mast that projects 60 m above the building.
8.1.6. Swiss Re. London
Height: 180 m. (41 floors). Largest floor external diameter (level 17): 56,15 m.
Completed in 2000. Architect: Foster & Partners Struct. Eng. Ove Arup & Partners. The
development of the building form is the result of synthesis of number of criteria.
Imaginative and strong architectural and structural concepts come together to create a
building that positively addresses all of these issues. The upper three levels of the
building from level 38 provide corporate facilities for Swiss Re and other tenants,
restaurant and upper viewing mezzanine offering 360º views over London. These levels
are enclosed with a steel and glass dome structure of 30 m diameter raising 22 m. from
its support on the top of the perimeter diagrid.
Tall building design for the Swiss Re building makes it possible to reduce the
footprint and help the office floors to be well proportioned for natural light.
The unique curved form developed generates also further benefits:
• the building streamlined aerodynamic shape protects against a windy environment at
street level
• the diameter of the building is able to gradually increase over the lower levels to
maximise the internal space relative to the footprint
• the reduction in floor diameter towards the plant floors at the top culminating in the
glazed domed roof, ensures that the building enhances but does not dominate the
London skyline.
The structural system of the building consists of internal core composed from 16
internal columns and external shell - perimeter “diagrid” structure.
The office floors are organised into six “spokes” or fingers, arranged on 1,5 m grid
around a circular service and lift core. Between the spokes are triangular zones that are
used as perimeter light-wells. The light-wells are offset at each successive floor by 5
degrees. This twist creates balconies at each level and opens up dramatic views through
and out of the building.
Perimeter “diagrid” structure was developed specifically for the Swiss Re building
in order to address the issues generated by the unusual geometry in a manner that was
fully integrated with the architectural concept and generated the maximum benefit for
the client.
• The final design solution avoids large cantilevers and keeps the light-wells free of
floor structure by inclining the perimeter columns to follow the helical path of the
six-fingered floors up trough the building.
• A balanced diagrid structure is formed by generating a pattern of columns spiralling
in both directions, intersecting at two- storey intervals at node points
• The columns are straight between nodes, with a change in direction and orientation
at each node point.
• This gives rise to significant horizontal forces at these points, even under balanced
gravity loading. These forces are carried by perimeter hoops at each node level,
rather than through the floor structure.
• The variation in the diagrid geometry results in compression in the hoops at the top
of the building (where the columns are more steeply angled and lighter loaded) and
very significant tension forces at the middle and lover levels.
• The horizontal hoops turn the diagrid into a very stiff triangulated shell, providing
excellent stability for the tower and equilibrium for any asymmetric or horizontal
loading conditions.
• This means that the core is not needed to resist wind forces and can be designated as
an open-planned steel structure providing adaptable internal space
8.1.7. Post Tower, Bonn, Germany
Height: 163 m 42 floors (OG) and 6 floors (UG). Completed in 2002.Archit.:
Murphy/Jahn Struct.: Werner Sobek Ing. Post Tower was chosen as 2nd best of the year
2002 out of 350 nominated buildings. It is an excellent example of Transparent
Post Tower structural system: internal shear wall core and perimeter columns. Both
parts of the building structure are connected by bracing on several levels and by
outrigger in technical floor. Interaction of the core with perimeter composite columns is
secured by stiff reinforced concrete floor slabs.
The R.C. slab has total thickness of 0,3 m and is supported by a suspender beam
running between the columns.
Each circle segment has two stiffening cores with a wall thickness of up to 0,8 m
and 19 steel composite pivoted columns of diameter varying between 762 and 406 mm
depending on the altitude at which they are installed.
The concrete cores are linked at five levels by means of diagonal stiffening crosses.
Further stiffening is provided halfway up the building, on the technical installations
level, by additional diagonal outriggers linking the cores with the external support
The envelope consists of second-skin façade, which allows windows to be opened
even on the upper levels and forms an integral part of the energy concept of the
building, which is based on minimal energy inputs. Part of this concept is also the water
cooling built into the reinforced concrete ceiling.
8.1.8. Taipei 101, Taipei, Taiwan
Height: 509 m (101 floors OG, 5 floors UG). Presently the highest building of the
world. Completion: 2004. Archit.: C.Y. Lee & Partn. Struct.: Thornton-Tomasetti
Taipei. 101 was designed for extreme loads which can appear in Taipei: typhoon winds
and heavy earthquake oscillations.
The footprint of the building is roughly 53-m square. The four exterior walls of the
lower 25 stories slope inward nearly 5º. Above that, eight stacked dimensionally
identical modules, each eight stories and with 7º outward-leaning façades rise to level
90. At the top are 11 mechanical equipment levels and 60m tall pinnacle, rising from
the 101 story up to 508m.
The stepped profile creates external safety decks at the base of each eight floor
module. Shelters inside these levels have fire fighting, smoke displacement and
communication equipment. Each module is isolated by smoke and fire barriers, and
contains independent security systems. Fire- and smoke-resistant safety stairways and
corridors also provide security.
Structural system: Internal core 22,5m square comprises 16 box columns in four
lines, which are generally fully braced between floors. Composite floors are typically
13,5cm thick. Eight Mega-columns 2,4 x 3,0m (at the base) arranged at the perimeter of
the building 22,5 m apart. Outriggers connecting internal core with mega-columns
arranged at the bottom of each 8 floor segments. From just bellow level 26 down,
mega-columns slope with the building’s profile. Two 2x1,2m columns are added
toward the center of each façade, while each corner is supported by an additional 1,4m
square sloping box column. Corner columns are tied to the main frame with two-storydeep belt trusses under levels: 9, 19, 27. All other sloping mega-columns are connected
to the core columns with double-story outriggers at these levels.
Main mega-columns are made of steel as thick as 80mm. Along with the core
elements, mega-columns are filled with 70 MPa reinforced concrete up to level 62.
Additional box columns below floor 26 are also filled.
To reduce building lateral accelerations and to satisfy the vibration and comfort
level requirement for the tower, a TMD system (Tuned Mass Damper) is designed and
installed at the top of the building. The TMD system is to employ a mass consisted of
built-up steel plate ball suspended by cable as simple pendulum from the 92 nd floor.
8.2. Examples of Buildings under Construction or in Designing Stage in the Height
Range around or over 500m.
8.2.1. Union Square (Phase 7) Hong Kong, China
Height: 484 m, Completion 2007, Architect.: Kohn Pedersen Fox Assoc., Struct.: Ove
Arup & Partners, Will be the tallest building in Hong Kong
8.2.2. Freedom Tower, New York City, USA
New design compromise between David Childs of Skidmore Owings and Merrill and
Daniel Libeskind. Height: 541m. Construction end: 2009. Twisting 70 storey structure
will feature 63 floors of office space topped by a lattice structure filled with energygenerating windmills and a spire reaching 541m. (1776 ft)
8.2.3. World Financial Centre, Shanghai, China
Height 492 m, Construction end: 2007. Architect.: Kohn, Pederson, Fox. The
foundation stone was laid on August 27 1997. Financial difficulties of developer from
Japan. No much progress reported.
8.2.4. International Business Center, Seoul, South Korea
Height: 580 m. Construction end: 2008. The top floors, from 104 – 130 will house the
hotel. The 46 mid-floors will be rented out to foreign residents as apartments. The 7th
to 57th low-floors will be for regional offices of foreign business.
8.2.5. Burj Dubai, Dubai, United Arab Emirates
Height: 705 m. Construction end: 2008 Archit. & Struct. SOM. The building will serve
residential, commercial, hotel, entertainment, shopping purposes. The design of Burj
Dubai is derived from the geometries of the desert flower, which is indigenous to the
region, and the patterning systems embodied in Islamic architecture. The tower is
composed of three elements arranged around a central core. As the tower rises from the
flat desert base, setbacks occur at each element in an upward spiraling pattern,
decreasing the mass of the tower as it reaches toward the sky. At the top, the central
core emerges and is sculptured to form a finishing spire. A Y-shaped floor plan
maximizes views of the Persian Gulf.
8.2.6. Russia Tower, Moscow, Russia
Height 648 m. Construction end: 2010. Archit. & Struct. SOM. Status: approved.
8.3. Examples of Interesting Solutions for Tall Building Projects which were not
8.3.1. 7, South Dearborn St. Chicago, USA, Height: 478 m
Archit. & Struct.: Skidmore Owings Merrill. Planned in 1999 as a new world’s tallest
building. The extremely narrow structure, would have occupied only about a quarter of
a city block. Designed as a mast-like tower, supporting 3 overhanging blocks of office
and residential floors at the middle and upper levels.
• Height to the roof top 478 m. - 108 stories; height to the top of telecommunication
antennae 610 m.
• Mixed use: parking on 11 floors, than the offices and above them residential space
on 40 high rise floors; telecommunication facilities on the top 13 floors.
• Six distinctive groups of floors are visible in the design.
• The structural design for the tower represents a major achievement in the
evolution of structural systems for super-tall buildings
• The unique structural system is termed “stayed mast” structure.
• The building is unusually slender of overall aspect ratio on nearly 8,5 : 1.
• The central spine “mast” of the system is composed of square (20 m on a side)
reinforced concrete core walls up to 1,2 m thick at the base.
• The core is linked and stabilised to the perimeter structure (“stays”) through multistory structural steel outrigger trusses (“spreaders) at two transitions points along
the tower shaft: at the parking/office and office/residential boundaries.
• The central core wall utilises high strength concrete up to 100MPa
• Foundations for the building are straight-shaft caissons socked 1.8 m into bedrock
and are designed to support a uniform load of 19MPa
• The top 137 m of the tower is composed of two telecommunication masts
specifically designed to broadcast digital television. The exterior perimeter of the
lowest 18 parking levels is composed of a continuous RC wall silo, which serves to
transfer a major portion of the overturning moment due to the wind to the perimeter.
• The upper residential and telecom. floors are cantilevered up to 9 m from the
central core walls allowing an uninterrupted panorama from these floors.
• The floor system for the upper cantilevered floors are tapered cast-in-situ
prestressed post-tensioned reinforced concrete beams and conventionally reinforced
one-way slabs.
• By cantilevering these floors, the core is essentially pre-compressed with gravity
loads, thus allowing the central core walls to withstand the full shear and
overturning moment due to wind above the lowest stay.
• The architectural design has been influenced by the structural solution in choosing
to express the cantilevered nature of the construction in the upper floors.
8.3.2. Miglin-Beitler Tower, Skyneedle, Chicago, USA. Height: 610 m.
This project was also not erected. But the structure designed for the building seems
to be interesting and following logical interaction of various elements of the system.
The 141 story, 610 m high (from street to roof) building was designed by Cesar Pelli
Associates and Thornton-Tomasetti structural engineers. The resulting cruciform tube
scheme offers structural efficiency, superior dynamic behavior, ease of construction
and minimal intrusion at leased office floors. The cruciform tube structural system
consists of the following six major components:
• a 19 by 19m concrete core
• eight cast-in-place concrete fin columns located on the faces of the building
• eight link beams connecting the four corners of the core to the eight fin columns at
every floor. In addition to enhance the interaction between exterior fin columns and
the core sets of two-story-deep outrigger walls are located at levels 16, 56 and 91.
• a conventional structural steel composite floor system
• exterior steel Vierendel trusses consisting of the horizontal spandrels and two
vertical columns at each of the 18,6m wide faces on the four sides of the building
between the fin columns.
• a 183m tall steel-framed tower at the top of the building