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TRENDS AND INNOVATIONS IN HIGH-RISE BUILDINGS OVER THE PAST DECADE ARCHIVES 1 by MASSACM I 1TT;r OF 1*KCHN0L0LGY Wenjia Gu JUL 02 2015 B.S. Civil Engineering University of at Urbana-Champaign, 2014 LIBRAR IES

SUBMITTED TO THE DEPARTMENT OF CIVIL AND ENVIRONMENTAL ENGINEERING IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF ENGINEERING IN CIVIL ENGINEERING AT THE INSTITUTE OF TECHNOLOGY

JUNE 2015

C2015 Wenjia Gu. All rights reserved.

The author hereby grants to MIT permission to reproduce and to distribute publicly paper and electronic copies of this thesis document in whole or in part in any medium now known of hereafter created.

Signature of Author: Signature redacted Department of Civil and Environmental Engineering May 21, 2015

Certified by: Signature redacted ( Jerome Connor Professor of Civil and Environmental Engineering Thesis Supervisor

Accepted bv: Signature redacted ?'Hei4 Nepf Donald and Martha Harleman Professor of Civil and Environmental Engineering Chair, Departmental Committee for Graduate Students

TRENDS AND INNOVATIONS IN HIGH-RISE BUILDINGS OVER THE PAST DECADE

by

Wenjia Gu

Submitted to the Department of Civil and Environmental Engineering on May 21, 2015 in Partial Fulfillment of the Degree Requirements for Master of Engineering in Civil and Environmental Engineering

ABSTRACT

Over the past decade, high-rise buildings in are both booming in quantity and expanding in height. One of the most important reasons driven the achievement is the continuously evolvement of structural systems. In this paper, previous classifications of structural systems are summarized and different types of structural systems are introduced. Besides the structural systems, innovations in other aspects of today's design of high-rise buildings including damping systems, construction techniques, systems as well as sustainability are presented and discussed.

To better understand current high-rise buildings, information about buildings above 200 meter completed within recent ten years and the current 100 tallest building in the world is collected and analyzed. Structural systems of worldwide 100 tallest buildings are discussed, from which trends are found. Data shows that tubular systems are in vast majority in recent high-rise building designs and an increasing number of buildings are using and composite materials instead of steel. Developments in structural systems also reduce structures' dependence on auxiliary damping devices. Additionally, sustainability has been given more and more consideration.

Thesis Supervisor: Jerome Connor Title: Professor of Civil and Environmental Engineering

3 4 TABLE OF CONTENTS

1. IN TRO D U C T IO N ...... 7

2. HIGH-RISE BUILDINGS ...... 9

2.1 D efinition ...... 9

2 .2 F acts ...... 10

2 .3 L o ad s ...... 13

3. STRUCTURAL SYSTEMS ...... 15

3.1 Previous Classifications ...... 15

3.2 Different Types of Structural Systems ...... 18

3.2.1 R igid Fram e ...... 18

3.2.2 Core and outrigger ...... 20

3.2.3 Framed ...... 22

3.2.4 Trussed Tube ...... 23

3.2.5 T ube in tube ...... 25

3.2.6 B undled system ...... 26

4. INNOVATIONS IN HIGH-RISE BUILDGINS ...... 28

4.1 Damping Systems ...... 28

4.2 Construction Techniques ...... 30

4.3 E levator System s ...... 32

5 TABLE OF CONTENTS

4.4 Sustainability ...... 35

5. ANALYSIS OF CURRENT HIGH-RISE BUILDINGS ...... 37

5.1 Structural System s ...... 37

5.2 Construction Materials ...... 39

5.3 Sustainability ...... 40

6. CASE STUDY OF ...... 42

7. CONCLUSION ...... 47

Al. REFERENCES ...... 48

A2. 100 TALLEST BUILINGS IN THE WORLD BY 2015 ...... 50

6 1. INTRODUCTION

Over the past decade, high-rise buildings are both booming in quantity and expanding in height over the whole world. The number of constructed buildings above 200 meters is increasing every year and the height of the world's tallest building has been raised from 508 meters in the year 2004 to 828 meters now. Some of the many reasons leading to this phenomenon include an expanding real estate market that emerges from the steadily growing global economy, providing investors and contractors with more and more opportunities, as well as the implicit competitions between countries, metropolitan areas, and to attract more global spotlight.

To fulfill the request of taller and taller buildings, engineers keep working on the optimization of structural systems to improve the structure's resistance over the load acting on it. Several studies have discussed the performance of different structural systems from different perspectives. Over the past decade, a number of high-rise buildings have adopted integrated structural systems that combined two or more basic structural systems, and innovative systems such as buttress core system can also be seen in completed buildings.

Besides the aspect of the structural system, structural material also plays an important role in

improving the structural stability and efficiency of the building.

Another important factor that helps pushing the limit of the height of buildings is the

development of construction techniques. With the help of high-tech construction equipment,

concrete can be pumped to a much higher distance than ever, even for high strength concrete.

7 Innovative construction methods also shortened the construction time so that for the owner the cost of developing a new high-rise building could be reduced.

Other considerations for the design of high-rise buildings including the damping system, fire design and emergency egress also have some changes over the past decade.

Nonstructural factors such as sustainability of the building are given more and more importance now.

Information about the 100 tallest completed buildings in the world has been collected. By studying the structural system as well as other properties of these 100 buildings, the current structural design trends can be found and comparisons between theoretical analysis and actual can be discussed, which will help engineers break the record of the most attractive high-rise building.

8 2. HIGH-RISE BUILDINGS

2.1 Definition

Before looking into the design trends and the innovations behind the increasing number of high-rise buildings over the past decade, it is important to define what high-rise buildings mean and what makes them different from other structures.

A tall building is referred as a multi-story structure in which most occupants depend on to reach their destinations. The most prominent tall buildings are called high-rise buildings in most countries (Challinger, 2008). Although these terms do not have internationally agreed definitions, a high-rise building, however, can be defined as follows:

According to the Council of Tall Buildings and Urban Habitat, a high-rise building is "a building whose height creates different conditions in the design, construction, and use than those that exist in common buildings of a certain region and period".

"Any structure where the height can have a serious impact on evacuation" (The

International Conference on Fire Safety in High-Rise Buildings).

"For most purposes, the cut-off point for high-rise buildings is around seven stories.

Sometimes, seven stories or higher define a high-rise, and sometimes the definition is more than seven stories. Sometimes, the definition is stated in terms of linear height (feet or meters) rather than stories. " (Hall, 2007)

Besides what is listed above, another important feature of a high-rise building is that it is the lateral load not the gravity load that governs the design of the structure. Lateral loads,

9 including wind load and , are crucial for high-rise buildings and can be resisted efficiently by choosing appropriate structural systems. The exact height above which a building can be defined as a high-rise building is specified by codes of the particular area where the building is standing.

2.2 Facts

As a representative of the development in high-rise buildings, the record of the tallest building in the world keeps being broken over the past decade. The 508-meter 101

Tower (Figure 1) which was opened on the last day of 2014 kept its title as the world's tallest building for a mere six years before the Bun Khalifa (Figure 2), standing at nearly

830 meters above the ground, stole its glory in the year of 2010. Yet once again, this glory

will be overshadowed in the near future by the 1000-meter-tall 's new

landmark, the, which is under construction now (Figure 3).

Figure 1: . Figure 2: Bur Khalifa. Figure 3: Kingdom Tower.

10 At the same time, the number of high-rise buildings completed is also increasing each year. Information about buildings that are over 200 meters completed each year from

2005 to 2015 is collected and analyzed. Results show that the number of completed buildings over 200 meters is basically increasing over time, and the average height of these buildings is increasing as well. As Figure 4 shows, the number of such buildings completed in 2014 is three times that in 2005, and the number of buildings above 200 meters is

expected to double by the end of 2015. For the height of completed buildings, as Figure 5

indicates, the average height of all buildings that are above 200 meters completed in the year

of 2015 is nearly 50% more than that in the year 2005. It is raised by almost 100 meters -

from 213 meters to 303 meters.

200 t84 180 160 140 120 100 807 80 2 40 . 20 : 0

Year of Completion

Figure 4: Number of completed buildings above 200m each year.

11 350 e 300 250 m 200

-150

100 50 0

Year of Completion

Figure 5: Average height of completed buildings above 200m each year.

For the current 100 tallest buildings in the world, as can be seen in Figure 6, there are only 28 buildings were completed before the year of 2005. As much as 72 buildings were completed within the past ten years. Researches in this paper are focused on these 72 high-rise buildings.

" Number of buildings completed between 2005-2015

" Number of buildings completed before 2005

Figure 6: Completion time of the 100 tallest buildings in the world.

12 2.3 Loads

The structural design of buildings is governed by all the loads that are acting on them. A standing structure is supposed to experience loads from two aspects - gravity loads and lateral loads.

Gravity loads are forces acting vertically on the structure such as the self-weight of the building, so they are the same for high-rise buildings and low-rise buildings unless the force will be larger at the bottom of high-rise buildings because of the accumulation of loads over height.

Lateral loads including wind loads and earthquakes, on the other hand, are crucial for the design of high-rise buildings. Wind loads will increase as the height of the buildings rises, and they act as pressures on the structure. Therefore, for buildings over certain height, there will be large lateral loads acting on it due to the wind. Besides the force resulted along the direction of the wind, dynamic effects of the wind should also be considered. The structure will also experience motion perpendicular to the direction of the wind, which is generated by the formation of vortex shedding acting on alternation sides of the structure.

The maximum displacement in the lateral direction generally occurs in the along-wind direction, while the peak accelerations of the structure occur in the cross-wind direction.

The is another important factor to consider in the design of high-rise buildings because of the intense vibration. This will result in the internal forces within the structure. To reduce the influence of earthquakes on the structure, the structure is supposed

13 to be as ductile as possible to avoid failure, and dampers are usually implemented in the structure.

14 3. STRUCTURAL SYSTEMS

The maximum height that a building can achieve is dependent on the ability of its structure to resist loads that are acting on it. The development of the structural system is a continuously evolving process. Since 1960 before which the predominant type of structural system was conventional rigid frame, the emergence of tubular systems, core and outrigger systems has helped to raise the height of buildings. Over the past decade, new developments in structural systems such as diagrid systems and buttressed core systems have been applied to the design of many high-rise buildings and showed satisfying performance in the resistance of gravity and lateral loads.

3.1 Previous Classifications

In 1969, classified structural systems for high-rise buildings relating to their heights with considerations for efficiency in the form of "Heights for

Structural Systems" diagrams for the first time (Khan, 1969). Later, these diagrams were upgraded by way of modifications (Khan, 1972, 1973). He developed these schemes for both steel and concrete buildings as can be seen in Figure 7. Feasible structural systems, according to him, are rigid frames, shear walls, interactive frame-shear wall combinations, belt , framed tubes, trussed tubes, tube-in-tube systems and other tubular systems.

15 140 130

710 I0 90 I .5 so z

40 30 Q? 78 20 I

RO F I

70 I

60-

50 0 40 I E I i 0 30

6) 20 -0 F. U, a

10 I i-S .I-- - ......

Figure 7: Classificationof high-rise building structuralsystems by F.R.Khan (above: steel; below: concrete).

Another classification of the structural system of high-rise building was developed in 2007 by Mir M. Ali. This classification is based on lateral load-resisting capabilities. He divided structural systems of high-rise buildings into two broad categories: interior structures and exterior structures, which was based on the distribution of the components of

16 ME I

the primary lateral load-resisting system over the buildings as shown in Figure 8 (Ali, 2007).

A system is categorized as an interior structure when the major part of the lateral load resisting system is located within the interior of the building. Likewise, if the major part of the lateral loading-resisting systems is located at the perimeter of the buildings, this system is categorized as an exterior structure.

160

U 140

120

60 0

Z0

410

20 t M < [II111 I

Conciee Broced Concee Conrte Oumgg.r Faed Frames- Sheor Wa + Shear Wd + Shea Wal + Stucul Frnm Concrete Steel Steel Hfnged Frames Se ald Ccncaele Rlome FAmI FCrume

17 IO

XM7

tune Ametuntue tue Ae * Ae

CCIO 9 t o eTLO COMCOMO S"0 a"M ecil>91o0n a"@ cam e fto 20. i Focanod Foslmwo lute Imed OP0080 Ongo uNXMOa koncw SLOP %WO TOMe FarnX

Figure 8: Classificationof high-rise buildingstructural systems by Mir A. Ali (above: interior structures; below: exterior structures)

3.2 Different Types of Structural Systems

3.2.1 Rigid Frame

The rigid frame structure, also called moment-resisting frame structure, is the most basic type of framing systems. It consists of horizontal (girders) and vertical (columns) members that are connected through rigid connections at the joint (Figure 9). Such framing systems resist loads primarily through the flexural stiffness of the structural members. The size of columns is mainly controlled by the gravity load, while the size of girders is controlled by the requirements of lateral sway of the building as well as the vertical deflection under dead and live loads. Because of the need for space in high-rise buildings, the number of columns should be minimized, which increases the span of girders. Therefore,

18 the size of girders will be increased to ensure the stability of the structure. Additionally, as the height of buildings increases, bending rigidity of both girders and columns should be increased to reduce the lateral deflection. Besides, the expense of the moment-resisting connections is really high. Therefore, the rigid frame would be an efficient structural system for buildings under 30 stories (Kowalczyk, Sinn, & Kilmister, 1995).

Connections must be capable of resisting bending moments

Deformed shape Bending moment diagram

Figure 9: Rigid frame.

19 3.2.2 Core and Outrigger

The core and outrigger system is another common structural system in high-rise buildings. The vertical core elements mostly consist of concrete shear walls or braced system to resist lateral loads. The outriggers are generally in the form of trusses in steel structures, or walls in concrete structures, which extend on both sides from the central core connecting the core to the perimeter of the building. The existence of outriggers can reduce the overturning moment in the core and can transfer the reduced moment to the outer elements as shown in Figure 10 (Taranath, 1998).

Shear wall or braced frame core Outrigger connected directly Column to core

20 _F

Moment in core with -- + \outrigger bracing \.--Moment in core without Leeward outrigger bracing columns in compression

Windward columns in tension

Figure 10: Core and outriggersystem.

Belt trusses are often combined in core and outrigger systems to distribute the

tensile and compressive forces to a large number of exterior frame columns, which are

located at the perimeter of the structure. Belt trusses also help in minimizing differential

elongation and shortening of columns. In the design of existing high-rise buildings,

outriggers are also supported by mega-columns in the exterior perimeter of the structure.

Some other advantages of the core and outrigger system includes that the exterior

column spacing can satisfy more aesthetic and functional requirements. For the aspect of

construction, the exterior framing system consists of simple beams and columns and does

not require moment-resisting connections as in rigid frame system, which is beneficial to the

construction process.

The core and outrigger system may be formed in any combination of steel, concrete

21 and composite construction. Because of the structural benefits of this system and the advantages listed above, the core and outrigger system has been very popular over the past decade.

3.2.3 Framed Tube

The framed tube system is the most basic tubular system in high-rise buildings.

The tubular system expresses the concept that a building can be designed as a hollow cantilever perpendicular to the ground to resist lateral loads by designing it. In the simplest framed tube system, the exterior perimeter of the structure consists of closely spaced columns that are tied together with deep spandrel beams through moment connections (Figure 11).

Closely spaced columns

I :b

Figure 11: Framed tube system.

22 For a framed tube under lateral loads, the corner columns experience the largest axial forces, and forces are distributed non-linearly along the direction parallel to wind and perpendicular to wind. This is because the axial forces in the middle columns of the frame lag behind that in the corner columns because that the structure acts like a hollow tube instead of a solid one. This phenomenon is called the shear lag effect, as shown in Figure 12.

In the design of framed tube system, the optimal purpose if to limit the shear lag effect.

Cosrmpive

Figure 12: Shear lag effect.

3.2.4 Trussed Tube

The trussed tube is a variation of the framed tube system. By adding large truss elements around the perimeter of the tube system, the bending stiffness of the structure can be increased, and the number of exterior columns can be decreased. The truss elements can also transfer some of the gravity loads acting as inclined column. At the same time, the

23 diagonals of a trussed tube connected to the joints of columns and beams effectively eliminate the effects of shear lag around the structure. Therefore, the space of columns in the perimeter of the building can be arranged more widely and the sizes of spandrel beams and columns can be designed smaller than the framed tubes (Khan, 1967).

Innovative structural systems over the past decade include diagrid systems and hexagrid systems (Figure 13). The difference between conventional trussed tube structures and the diagrid system is that almost all conventional vertical columns can be eliminated for diagrid structures. This is because the diagonal members in diagrid structural systems can carry both gravity loads and lateral loads through their triangulated configuration (Panchal and Patel, 2014). The hexagrid system, also called beehive system, is another evolutionary structural system in the design of high-rise buildings. In addition to eliminating perimeter columns, another noticeable advantage of the hexagrid systems is that each structural element can be optimized. This is a relatively new idea and more exploration is required for the implement of this structural system in the design of high-rise buildings (Askarinejad,

2012).

Z N/ NZ

Z NZ N 4 N I

Figure 13: Trussed tube systems (Left: conventional trussed tube; middle: diagridsystem;

24 right: hexagrid system).

3.2.5 Tube in Tube

The tube in tube system uses the core to resist part of the lateral loads in order to enhance the stiffness of the tubular systems. This structural system consists of an outer tube in the perimeter and a core tube inside the structure. The core tube inside could be made of a framed tube, a trussed tube or a solid tube holding elevators and other services. The floor system connecting the core and the exterior tube transfers the lateral loads to both systems, while the exterior tube system carries more loads because its greater structural stiffness

(S.R.S.Kuman and A.R.S. Kuman, 2014).

The tube in tube system is flexible in materials because the two tube systems can be constructed using completely different materials. Current designs of high-rise buildings combine concrete shear wall core with outer steel framed tube, which is an efficient system

in resisting of different types of loads and has been widely implemented. Figure 14 shows the floor plan of a typical tube in tube structure, which is the Trade Center, located in

Beijing, China. The structure of this building consists of a concrete core and the exterior

steel framed tube.

25 Figure 14: Floorplan of typical tube in tube system.

3.2.6 Bundled system

The bundled tube structural systems in a combination of several individual tubes connected together to act as a single unit. The structural stiffness of the building is notably increased. In this system, the shear lad effect in the flanges is largely reduced by the existence of the internal webs. The bundled tube system also allows wider column spacing in the tubular walls, and the stress in columns is distributed more evenly than that in a single tube system.

One of the most typical bundled tube systems is the 110-story completed in 1974 which was also the first buildings using such systems. There are nine steel framed tubes in total bundled at the bottom of the buildings and they are terminated in different heights as Figure 15 shows. Such structural system provides the high-rise building with new possible appearance instead of the simple boxlike shape.

26 D 110

Section D-D 90

66

Section C- C 50

30

Section 8 B A

Section A-A

Figure 15: Structuralsystem of Willis Tower.

One innovative structural system using the bundled form over the past decade is the buttressed core system, which was implemented in the design of Burj Khalifa. The most important factor of this system is a tripod-shape structure in which a strong concrete core in anchors three structural elements arranged around it. The structure of Burj Khalifa will be discussed more in the case study section later.

27 4. INNOVA TIONS IN HIGH-RISE B UILD GINS

4.1 Damping Systems

As the evolution of structural systems and development in construction materials especially high-strength concrete, the weight of the high-rise building has been decreased considerably than that of earlier ones. Lighter structures reduce cost as well as the construction time. However, they may cause serious structural motion problem due to the wind load. An implement of damping systems will help control the structural motion.

Damper can reduce not only the amount of lateral displacement but also the acceleration of the structure. Structures with more damping can reduce the magnitude of vibration and dissipate the vibration more quickly (Moon, 2005).

Damping system can be divided into two categories, passive damping systems and active damping systems. Passive damping systems have fixed properties and they do not need energy to perform as intended, while active damping systems do need energy input

serving as actuators to modify the damping system properties under different load cases.

Therefore, active damping systems are more efficient than passive systems. However, passive damping systems are more commonly used in high-rise buildings because of the cost

and reliability.

Passive damping systems can be further divided into two subcategories, auxiliary mass systems to generate counteracting forces such as tuned mass dampers (TMD) and

tuned liquid dampers (TLD), and energy dissipating materials based systems such as viscous

28 dampers and visco-elastic dampers.

Active damping systems are a more advanced form of performance driven technologies, which is the tendency of today's high-rise building design. Examples include active mass dampers (AMD) and active variable stiffness devices (AVSD). Different types of auxiliary damping systems are summarized in Figure 16 (Connor, 2003).

Tuned Mass Dampers ( TMD)

Tuned Lquid Dampers (TLD)

Vicus Dampers_

Passive System Viscoelassk Dampers

Hysteretic Dampers

Fricton Dampers -Etem4Aagne Dampers

Active Mass Dampers (AMD) Acive System Acive Various Stifless (AVS) Devices

Figure 16: Various types of auxiliary damping systems.

However, it is noticeable that as the continuously evolvement of structural systems

more and more high-rise buildings do not need additional damping systems anymore. The

property of the structure itself is sufficient to protect the building from vibrations due to

29 wind. Such structural factors that will help decrease the dependence of high-rise buildings on auxiliary damping systems include bundled systems, twisted shape of the building and opening at the top, as shown in Figure 17. , which is located in , implemented no additional damping systems. The stiffness and weight of the building, combined with the asymmetric setbacks, laterally support and stabilize ad minimize perceptible motion.

Figure 17: Buildings using geometries to reduce reliance on auxiliary damping systems (left 1 &2: bundled systems; middle: opening at top; right 1 &2: twisted shapes).

4.2 Construction Techniques

While structural engineers managed to find a plan for buildings to rise out of the

ground theoretically or experimentally, it still remains a challenge for contractor to actually

30 build it. As the height of high-rise buildings increases, so does the challenge contractors face.

Construction teams not only have to erect steel and concrete members, they also have to do it precisely, safely, time and cost efficiently and environmentally friendly. Therefore, construction techniques have to be developed.

Being time efficient not only means that the building can open to public sooner, but also means lower construction cost. An innovation applied in the construction of in is the top-down construction method. It allowed the first 23 stories of the concrete core and much of the surrounding tower to be built before the basement had been fully excavated. This technique was a world first and saved four months time and a huge amount of budget on the complex program.

As the development of construction materials especially the creation of high-strength concrete, more and more high-rise buildings start to use concrete to construct the structure. Having more powerful pump means high that high-strength concrete is able be delivered to high levels at greater speed. The KK100 in set a record of pumping high-strength C 120 grade concrete to the height of 417 meters.

To guarantee workers' safety, precaution for hazard prevention has to be taken seriously. During construction of Doosan Haeundae We've the Zenith Tower, to prevent spalling, which is the explosion that can occur when the concrete is exposed to high temperatures, contractors built the tower with high strength concrete using a spalling failure prevention method.

31 To make sure the building is in its upright position, GPS technology has been used over the past decade. This would not have been possible before satellites and GPS technologies were mature. The , which is located in , utilized

Leica Geosystems Core Wall Survey Control System, a procedure developed by Leica

Geosystems using GPS observations combined with a precision inclination sensor to provide reliable coordinated points at the top of the building. Another example is used in the construction of in , where vortex shedding suppression devices based on simple principles were used as temporary measures during the construction stage to prevent excessive wind induced movement of the spire.

4.3 Elevator Systems

As the height of high-rise building increases rapidly, the upgrade of many of its accessories is required. One of the developed accessories is the elevator system. For high-rise buildings, efficient mobility is an absolute necessity. Past elevators are incompatible with today's super-tall buildings, as they have relatively slow rising and descending rates, causing much time loss when traveling between high levels; some elevator shafts are so large in size that they take up much of the level's space; some buildings are so tall that the steel elevator cables are close to the limit where they can no more carry their own weight.

During the past decade, various technical advancements are seen in the elevator

32 system of high-rise buildings. One smart design is the double deck elevator (Figure 18). As the name indicates, the double deck elevator consists of two individual cars attached together, one on top of the other. Both cars operate in the same elevator shaft. Such a scheme could increase efficiency dramatically during high traffic periods. During such time, single elevator would stop at every floor, but the double deck elevator will only stop at every other floor as one of its cars transport passenger on odd floors and the other transport passengers on even floors. Besides the improved efficiency in elevator shaft usage, the operation speed of the elevator has also increased throughout the years. Table 1 below shows the comparison of elevator speed of some of the world's famous buildings. It can be seen that the speed has increased in the last few decades. The improvement in elevator speed is accompanied by more powerful magnetic motors, high-tech air pressure adjustment systems, and lighter and stronger materials. Finnish manufacturer Kone has developed a carbon fiber dubbed UltraRopeTM that is seven times lighter than steel cables (Figure 19).

The UltraRopeTM will be used in the 1000-meter-tall Kingdom Tower, Saudi Arabia, which is under construction.

Currently, engineers are picturing elevator systems that will travel both vertically but also horizontally. As elevators will carry passengers horizontally, vertical shafts could be

reduced, thus saving floor spaces. ThyssenKrupp is poised to revolutionize elevator power

system by using magnetic drive similar to that seen on a Maglev train. The system will be

the world's first cable-free elevator and counter-weight free.

33 Building Completion Year Elevator Speed (m/s) , City 1930 4.5 Building, 1931 7.1 Willis Tower, Chicago 1974 8.1 Taipei 101, China 2004 16.8 Tower, Shanghai 2015 18 CTF Finance Tower, 2016 20 (expected)

Table 1: Comparison of elevator speed of some of the worlds famous buildings.

Coss, 440.MV *kVWwwM -of NWe-

we-IR010

Figure 18: Scheme of double deck elevator

Elevator moving masses (kg) 108600

13900

Steel Cable UltraRope"

Figure 19: Comparison of traditionalsteel cable to Kone UltraRopeT M .

34 4.4 Sustainability

Over the past decades, more and more factors besides structural and constructional aspects are taken into consideration in the design of high-rise buildings. As global warming and fossil fuel are becoming increasingly concerned topics, engineers are challenged to put further effort into designing buildings that are more environmentally friendly. Measures that care most commonly seen in achieving the sustainability of high-rise buildings can be categorized into two aspects - constructional and operational.

Constructional sustainability is the measures taken during the construction process.

These measures include purchasing construction materials locally or regionally, thus reducing total mileage of transportation, which in turn reduced carbon footprint. Another measure is to reuse and recycle excess materials. In excess of 95% of structural steel was recycled after the construction of New York Times Building, New York City.

Analogously, operational sustainability indicates the measures taken after the completion of construction and during its normal operation. One of the most common measure is the use of double-sided windows or double wall curtains with low-emissivity coating to improve thermal insulation (Figure 20). Additionally, use of LED lights for signage will reduce electricity consumption significantly. The Shanghai World Financial

Center features over 7000 LEDs, and the power consumption for its signage is merely 220

KW, which is much lower than even the shorter buildings around it. Buildings by rivers or seas can reduce energy cost by using river or seawater to cool the buildings. An example is

35 the Trump Tower in Chicago that utilizes water from the to cool the building.

The cooling system allows the water to recirculate back to the river. Building in high sunshine areas can install solar panel to heat water. Bun Khalifa features solar panels that are capable of heating 140,000 liters of water daily. In cities where pollution is heavy, buildings have air filtration and circulation system to guarantee occupants breathe clean air.

In recognition of and to promote sustainability in building, the U.S Green Building Council

(USGBS) awards the Leader in Energy and Environmental Design (LEED) certificate to buildings that are outstanding in sustainability. The certification has four levels - certified,

silver, gold, and platinum. The Taipei 101, which is located in Taipei City, has been

awarded the LEED Platinum certificate and will set the quality and performance benchmark

for super-tall buildings.

Figure 20: Double skinnedfacade curtain wall system.

36 5. ANALYSIS OF CURRENT HIGH-RISE BUILDINGS

To better understand the implement of different structural systems, construction materials and design critics of high-rise buildings in the actual world, information about high-rise buildings above 200 meters completed in the past ten years as well as the current

100 tallest buildings in the world has been collected and analyzed.

5.1 Structural Systems

Based on the properties of different types of structural systems which are introduced in previous section, structural systems of modem high-rise buildings are divided into seven categories: rigid frames, core and outrigger systems, framed tubes, trussed tubes, tube in tube systems and bundle systems. The results have been shown in Figure 21 and

Figure 22.

Figure 21 shows the distribution of structural systems of high-rise buildings above

200 meter completed during each period over time. As the figure shows, tube in tube systems have been more and more used in the design of high-rise buildings, while rigid frame systems is no more been used within the past five decades.

Figure 22 shows the distribution of structural systems of the current worldwide 100 tallest buildings. As can be seen, vast majority of the structural system consist of tubular

systems and core and outrigger systems, in which the tube in tube system has the largest percentage of 38%.

37 16

14

12 " Bundled system 10 " Tube in tube

5* - " Trussed tube " Framed tube 6 N Core and outrigger 4, * Rigid Frame ... 2......

Figure 21: Distributionof structuralsystems of buildings over 200m over time.

2%

0 Bundled system

U Tube intube 8 Trussed tube a Framed tube M Core and outrigger 0 Rigid Frame

Figure 22: Distributionof structuralsystems of the current 100 tallest buildings.

Taking the average stories of different types of structural systems of the current 100 tallest buildings in the world, comparison can be conducted with previous theoretical analysis of structural systems. As Figure 23 shows, bundle system has the highest average

38 number of stories, while core and outrigger system has the lowest average number of stories.

Rigid frame system has the second highest average number of stories, which is quite different from previous analysis, because of relatively small sample size.

100 90

; 80 70 60 s0 40 30 20 10 0 Core and Tube in Framed Trussed Rigid Bundled outrigger tube tube tube Frame system

Figure 23: Average number of stories of different types of structuralsystems.

5.2 Construction Materials

To study the trend of construction materials, information about worldwide 100

tallest buildings in each period is collected. Result is shown in Figure 24.

A steel building is defined as a building where the main vertical and lateral

structural elements and floor systems are constructed from steel. Similarly, a concrete

building is defined as one where the main vertical and lateral structural elements and floor

systems are constructed from concrete. A composite building utilizes a combination of both

steel and concrete acting compositely in the main structural elements. A mixed-structure

39 building is any building that utilizes distinct steel and concrete systems above or below each other.

As the figure indicates, a high percentage of buildings are using composite materials in the past few decades. The most common combination is a steel building with a concrete core. At the same time, the number of buildings using concrete as the construction materials is increasing as well. One possible reason behind the increasing number of concrete buildings is the development of high-strength concrete and concrete pumping techniques which have been discussed previously.

100

* Unknown 75 " Mixed 50 a Composite " Concrete 25 " Steel 0 1960 1970 1980 1990 2000 2005 2010 2015

Figure 24: Distributionof construction materials of 100 tallest buildings in each period.

5.3 Sustainability

Since the matter of sustainability has been given more and more consideration in

recent years, the sustainable design of 72 buildings completed in the past decade that are

40 listed in the current 100 tallest buildings is studied besides the aspects of structural systems and construction materials. Result is shown in Figure 25.

As the result shows, 43 percent of buildings have considered sustainability in their design, and most of them are awarded LEED certificates. According to the data collected,

most popular measures of sustainable design of high-rise buildings include double-sided

windows or double curtain walls to provide thermal protection and water recycling and air

filtration systems.

* Number of buildings considering sustainability * Number of buildings without considering sustainability

Figure 25: Distribution of buildings consideringsustainability.

41 6. CASE STUDY OF BURJ KHALIFA

At 828 meters, the Burj Khalifa (formerly the Burj Dubai) has 163 stories and is the world's tallest freestanding structure as well as the world's tallest building (Figure 26).

Construction of the tower began in January 2004 and the structure was topped out in

October 2009. It was officially opened in January 2010. The architectural and engineering designer of this tower was Skidmore, Owings and Merill (SOM) of Chicago and its primary contractor is Engineering and Construction Group of .

Figure 26: Bur Khalifa.

The structural system of Buj Khalifa is buttressed core system that is mentioned

above. It is designed to efficiently support a super-tall building utilizing a strong central core,

buttressed by its three wings. The vertical structure is tied together at the mechanical floors

through outrigger walls in order to maximize the building's stiffness. It is an inherently

42 stable system in that each wing is buttressed by the other two. The central core provides the torsional resistance for the building, while the wings provide the shear resistance and increased moment of inertia. The result is an efficient system where all of the building's vertical structure is used to resist both gravity and lateral loads (Figure 27).

wing

central core

corridor wall

Figure 27: Typicalfloor plan of Bur Khalifa.

The structural integrity of the building itself can also serve as the damping system.

The building rises to the heavens in several separate stalks, which top out unevenly around

the central spire. This somewhat odd-looking design deflects the wind around the structure

and prevents it from forming organized whirlpools of air current, or vortices, that would

rock the tower from side to side and could even damage the building. The variation of the

tower shape, and width, resulted in wind vortices around the perimeter of the tower that

behaved differently for different shapes at different frequencies, thus disorganizing the

43 interaction of the tower structure with the wind (Figure 28). Over 40 wind tunnel tests were conducted on Burj Khalifa to examine the effects wind would have on the tower and its occupants. Engineers determined that no tuned-mass damping was needed.

VM T~-

PWoo

Lower Pan

Figure 28: Wind profile around Bur] Khalifa.

During the construction process, over 45,000 m3 of concrete weighing more than

110,000 tons were used to construct the concrete and steel , which features 192 piles. Each pile is 1 .5m in diameter and 43m long buried more than 50m deep. The

construction of Burj Khalifa's used 330,000 m3 of concrete and 39,000 tons of steel rebar.

Special mixes of concrete are made to withstand the extreme pressure of the massive

building. It was difficult to create a concrete that could withstand both thousands of tons

bearing down on it and high temperatures that can reach 50 0C (122 0F). To

44 combat this problem, the concrete was not poured during the day. Instead, it was poured at night when the air is cooler and the humidity is higher, and during the summer months ice was added to the mixture. In November 2007, the highest core walls were pumped using 80 MPa concrete from ground level to the height of 606 meters, which broke the previous pumping record of 470m in the Taipei 101.

At the aspect of elevator systems, eight escalators and 57 elevators were installed in

Burj Khalifa, of which two are double-deck elevators used exclusively for the travel to the . Engineers of Bun Khalifa considered triple deck elevators at first, but the

final design called for double deck elevators. With the rising and descending speed up to

1Om/s, these are the world's fastest double-deck elevators. The elevator system of this tower

is also awarded as the longest travel distance elevator in the world that is 504 meters, and the

world's highest elevator which lands at 638 meters (Otis, 2010).

Burj Khalifa is also considered as a sustainable building. Solar panels are capable of

heating 140000 liters of water daily. A special performance glazing glass with low

emissivity provides the tower with advanced thermal protection. Due to its significant height,

the building is able to utilize ventilation from where air temperature is cooler and humidity

is relatively lower. When air is drawn in at the top of the building, it requires less energy for

, ventilation, and dehumidification system. LED modules used for signage

throughout to ensure reliable low maintenance lighting with low energy consumption.

Additionally, Burj Khalifa has one of the largest condensate recovery systems in the world.

45 Collecting water from air conditioning condensate discharge prevents it from entering the wastewater stream and reduces the need for municipal potable water (Burj Khalifa,

CTBUH).

46 7. CONCLUSION

Over the past decade, both the number of high-rise buildings and the average height of high-rise buildings have increased rapidly. Continuously evolving structural systems creates opportunities for structures to be more efficient. Other developments in construction techniques, accessory systems as well as structural materials have enabled the structure to actually stand taller and taller.

Based on the study of recent high-rise buildings and the current 100 tallest buildings in the world, following trends can be summarized: By the year of 2015, tubular structures are in vast majority of the structural systems in recent high-rise buildings, in which tube in tube system is the most popular one and has been applied in the design of a large number of high-rise buildings. Advancements in structural systems also help to reduce buildings' dependence on auxiliary damping devices. For structural materials, there is an increasing trend to use concrete and composite materials to construct the structure. Additionally, sustainability has been given more consideration in modem high-rise building designs.

47 Al. REFERENCES

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Ali, M.M. (2001). "Art of the : The Genius of Fazlur Khan". New York: Rizzoli.

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Baker, W. F. (2001). "Structural Innovation." Sixth World Congress on Tall Buildings and Urban Habitat. , Australia.

Challinger, D. "From the Ground Up: Security for Tall Buildings CRISP Report". Alexandria, VA: ASIS Foundation Research Council; 2008.

Connor, J.J. (2003). Introductionto StructuralMotion Control.

Hall, Jr JR (2005). "High-Rise Building Fires". Quincy, MA: National Fire Protection Association.

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Khan, F.R. (1969). "Recent structural systems in steel for high-rise buildings". In Proceedings of the British Constructional Steelwork Association Conference on Steel in Architecture. London: British Constructional Steelwork Association.

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Khan, F.R. (1973). "Evolution of structural systems for high-rise buildings in steel and concrete". In J. Kozak (Ed.), Tall Buildings in the Middle and East Europe: Proceedings of the 10th Regional Conference on Tall Buildings-Planning, Design and Construction. Bratislava: Czechoslovak Scientific and Technical Association.

Kumar, S.R.S.; Kumar, A.R.A.. "Advanced structural forms". Design of Steel Structures. Indian Institute of Technology Madras.

Moon, K. (2005). "Dynamic Interrelationship between Technology and Architecture in Tall Buildings". Unpublished PhD Dissertation, Massachusetts Institute of Technology.

48 Otis (2010). "Burj Khalifa, the world's tallest building, inaugurated: Global press and first visitors ride Otis elevators to observation deck". (May 20, 2015)

Panchal, N.B.; Patel,V.R. (2014). "Diagrid structural system: strategies to reduce lateral forces on high-rise buildings". International Journal of Research in Engineering and Technology, Volume: 03 Issue: 04

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Taranath, B. S. (1998). Steel, Concrete, & Composite Design of Tall Buildings. Second Edition. McGraw-Hill. New York, NY.

49 A2. 100 TA LLEST BUILINGS IN THE WORLD BY 2015

# Building Name City Height Floors Completed Material (m) 1 Buj Khalifa Dubai (AE) 828 163 2010 steel/concrete 2 Shanghai (CN) 632 128 2015 composite Makkah Royal 3 Mecca (SA) 601 120 2012 steel/concrete Tower New York 4 541.3 94 2014 composite City (US) 5 TAIPEI 101 Taipei (TW) 508 101 2004 composite

6 6 Shanghai World Financial Shanghai (CN) 492 101 2008 composite Center International Commerce 2010 composite 7 Centre (CN) 484 108 Kuala 8 Petronas Tower 1 451.9 88 1998 composite _____Lumpur (MY) Kuala 9 Petronas Tower 2 451.9 88 1998 composite _____Lumpur (MY) 10 (CN) 450 66 2010 composite 11 Willis Tower Chicago (US) 442.1 108 1974 steel 12 KK100 Shenzhen (CN) 441.8 100 2011 composite 13 Guangzhou Intemnational 13 Cnter Guangzhou (CN) 438.6 103 2010 composite Finance Center 14 Dubai (AE) 426.5 101 2015 concrete 15 432 New York (US) 425.5 88 2015 concrete 16 Trump International Hotel 16 ter Chicago (US) 423.2 98 2009 concrete & Tower 17 Shanghai (CN) 420.5 88 1999 composite 18 Dubai (AE) 413.4 101 2012 steel/concrete 19 Al Hamra Tower (KW) 412.6 80 2011 concrete Two International Finance composite 20 Centre Hong Kong (CN) 412 88 2003

21 Dubai (AE) 392.4 88 2012 concrete 22 CITIC Plaza Guangzhou (CN) 390.2 80 1996 concrete

23 Capital Market Authority (SA) 385 76 2015 composite Tower 24 Shenzhen (CN) 384 69 1996 composite

50 25 Eton Place Dalian Tower 1 Dalian (CN) 383.1 80 2015 composite

26 Burj Mohammed Bin (AE) 381.2 88 2014 concrete Rashid Tower New York 27 City (US) 381 102 1931 steel

28 Dubai (AE) 380.5 87 2012 concrete Concrete 29 Central Plaza Hong Kong (CN) 373.9 78 1992

Federation Towers - 30 Vostok Tower (RU) 373.7 95 2015 concrete

31 Bank of China Tower Hong Kong (CN) 367.4 72 1990 composite 32 Bank of America Tower New York (US) 365.8 55 2009 composite 33 Almas Tower Dubai (AE) 360 68 2008 concrete

34 JW Marriott Marquis Dubai (AE) 355.4 82 2012 concrete Hotel Dubai Tower 1

35 JW Marriott Marquis Dubai (AE) 355.4 82 2013 concrete Hotel Dubai Tower 2 36 Emirates Tower One Dubai (AE) 354.6 54 2000 composite 37 OKO - South Tower Moscow (RU) 353.6 85 2015 concrete 38 The Torch Dubai (AE) 352 86 2011 concrete 39 Tower 1 (CN) 350.6 68 2015 composite 40 Guangzhou (CN) 350.3 60 2012 concrete 41 T & C Tower (TW) 347.5 85 1997 composite 42 Center Chicago (US) 346.3 83 1973 steel 43 The Center Hong Kong (CN) 346 73 1998 steel 44 Chicago (US) 343.7 100 1969 steel 45 ADNOC Headquarters Abu Dhabi (AE) 342 76 2015 concrete Ahmed Abdul Rahim Al 46 Aed Tb wer Dubai (AE) 342 76 2015 steel/concrete Attar Tower Wuxi International 47 Finnaioal Wuxi (CN) 339 68 2014 composite Finance Square______

48 48 ChongqingF in Cnr World Chongqing (CN) 338.9 72 2015 composite Financial Center 49 Moscow (RU) 338.8 75 2013 concrete 50 Tianjin World Financial 50 Tianjin (CN) 336.9 75 2011 composite Center P S C 3 6 51 Shimao International Plaza Shanghai (CN) 333.3 60 2006 concrete

51 52 Dubai (AE) 333 71 2007 composite 53 (CN) 331 68 2008 steel 54 China World Tower (CN) 330 74 2010 composite Keangnam Hanoi 55 Hanoi (VN) 328.6 72 2012 concrete Landmark Tower 56 Longxi International Hotel Jiangyin (CN) 328 72 2011 composite 57 Al Yaqoob Tower Dubai (AE) 328 69 2013 concrete 58 Wuxi Suning Plaza 1 Wuxi (CN) 328 68 2014 composite 59 Dubai (AE) 326 80 2010 concrete 60 Abu Dhabi (AE) 324 72 2013 concrete 61 Nanjing (CN) 324 62 2013 composite Yantai Shimao No. 1 The 62 Yantai (CN) 323 59 2015 composite Harbour 63 QI Tower Gold Coast (AU) 322.5 78 2005 concrete 64 Trade Center Wenzhou (CN) 321.9 68 2011 concrete 65 Dubai (AE) 321 56 1999 composite 66 Hong Kong (CN) 320.4 80 2006 concrete New York 67 Chrysler Building City (US) 318.9 77 1930 steel

New York 68 New York Times Tower 318.8 52 2007 steel City (US) Riverside Century Plaza 69 Wuhu (CN) 318 66 2015 composite Main Tower 70 HHHR Tower Dubai (AE) 317.6 72 2010 concrete 71 Bank of America Plaza Atlanta (US) 311.8 55 1992 composite 72 Moi Center Tower A Shenyang (CN) 311 75 2014 composite 73 U.S. Bank Tower Los Angeles (US) 310.3 73 1990 steel Kuala 74 Menara Telekom 310 55 2001 concrete Lumpur (MY) 75 Dubai (AE) 310 83 2010 concrete 76 Tower Guangzhou (CN) 309.4 71 2013 composite 77 Guangzhou (CN) 309.4 73 2015 composite 78 Emirates Tower Two Dubai (AE) 309 56 2000 concrete 79 Riyadh (SA) 307.9 68 2014 concrete The Franklin - North 80 Chicago (US) 306.9 60 1989 composite Tower Chi (U) 306.9 60 1989 composte 81 Dubai (AE) 306.4 73 2013 concrete

52 82 New York (US) 306.4 75 2014 steel/concrete East Pacific Center Tower 83 A Shenzhen (CN) 306 85 2013 concrete

84 The Shard London (GB) 306 73 2013 composite 85 JPMorgan Houston (US) 305.4 75 1982 composite 86 T2 Abu Dhabi (AE) 305.3 80 2011 concrete Northeast Asia Trade 87 t e r Incheon (KR) 305 68 2011 composite Tower 88 Baiyoke Tower II Bangkok (TH) 304 85 1997 concrete

89 Wuxi Maoye City - Wuxi (CN) 303.8 68 2014 composite Marriott Hotel 90 Chicago (US) 303.3 64 1990 concrete

91 Shenzhcn Changcheng Shenzhen (CN) 303 61 2014 composite Center 92 Greenland Puli Center Jinan (CN) 303 60 2015 composite 93 Leatop Plaza Guangzhou (CN) 302.7 64 2012 composite 94 Wells Fargo Plaza Houston (US) 302.4 71 1983 steel 95 Riyadh (SA) 302.3 41 2002 steel/concrete 96 The Address Dubai (AE) 302.2 63 2008 concrete Capital City Moscow 97 Moscow (RU) 301.8 76 2010 concrete Tower 98 (QA) 300 36 2007 composite 99 Kuwait City (KW) 300 60 2009 concrete Doosan Haeundae We've 100 the Zen We Busan (KR) 300 80 2011 concrete the Zenith Tower A

53