Summer School URBAN STEEL STRUCTURES July 11 – 15, 2005 Gdańsk, Poland

TALL BUILDINGS – PAST, PRESENT AND FUTURE DEVELOPMENTS

R. KOWALCZYK 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

Mission: • 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 implementation.

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, www.ctbuh.org, info@ctbuh.org. Correspondence: Geri Kerry, Council on Tall Buildings and Urban Habitat, PO Box 4363Bethlehem, PA. USA 18018 email gkery@ctbuh.org.

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ChairmanRon Klemencic, Skilling Ward Magnusson Barkshire, Seatle, USA. Executive Director Director Emeritus David M. Maola 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

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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

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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

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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 envelope.

• 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 existence.

• 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

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this presentation. • The source of presented figures is either CTBUH slide collection or Internet:

www.skyscrapers.com. 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

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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 core)

• 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

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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 structure.

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.

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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

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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

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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).

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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 cast-in 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

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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 capabilities.

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.

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• 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 evacuation.

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

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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 restaurant-goers”.

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

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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

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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.

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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,

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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 Building.

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 cores.

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

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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-story-deep 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 energy-generating 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

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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 erected 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 multi-

story 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

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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

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