1. BURJ KHALIFA
b
Burj Khalifa (Arabic: برج خليفة
"Khalifa Tower"), known as Burj Dubai prior to its inauguration, is a
skyscraper in Dubai, United Arab Emirates, and is currently the tallest
structure in the world, at 828 m (2,717 ft). Construction began on 21 September
2004, with the exterior of the structure completed on 1 October 2009. The
building officially opened on 4 January 2010
The building is part of the new 2 km2 (490-acre) flagship development called Downtown Dubai at the 'First Interchange' along Sheikh Zayed Road, near Dubai's main business district. The tower's architecture and engineering were performed by Skidmore, Owings, and Merrill of Chicago, with Adrian Smith as chief architect, and Bill Baker as chief structural engineer. The primary contractor was Samsung C&T of South Korea.The total cost for the project was about US$1.5 billion; and for the entire "Downtown Dubai" development, US$20 billion.
2. FACTS ABOUT BURJ DUBAI
Milestones
·
January 2004: Excavation commences.
·
February 2004: Piling starts.
·
21 September 2004: Emaar contractors begin construction.
·
March 2005: Structure of Burj Khalifa starts rising.
·
June 2006: Level 50 is reached.
·
February 2007: Surpasses the Sears Tower as the building with the most
floors.
·
13 May 2007: Sets record for vertical concrete pumping on any building
at 452 m (1,483 ft), surpassing the 449.2 m (1,474 ft) to which concrete was
pumped during the construction of Taipei 101, while Burj Khalifa reached 130
floor.
·
21 July 2007: Surpasses Taipei 101, whose height of 509.2 m (1,671 ft)
made it the world's tallest building, and level 141 reached.
·
12 August 2007: Surpasses the Sears Tower antenna, which stands 527.3 m
(1,730 ft).
·
12 September 2007: At 555.3 m (1,822 ft), becomes the world's tallest
freestanding structure, surpassing the CN Tower in Toronto, and level 150
reached.
·
7 April 2008: At 629 m (2,064 ft), surpasses the KVLY-TV Mast to become
the tallest man-made structure, level 160 reached.
·
17 June 2008: Emaar announces that Burj Khalifa's height is over 636 m
(2,087 ft) and that its final height will not be given until it is completed in
September 2009.
·
1 September 2008: Height tops 688 m (2,257 ft), making it the tallest
man-made structure ever built, surpassing the previous record-holder, the
Warsaw Radio Mast in Konstantynów, Poland.
·
17 January 2009: Topped out at 828 m (2,717 ft).
·
1 October 2009: Emaar announces that the exterior of the building is
completed.
·
4 January 2010: Burj Khalifa's official launch ceremony is held and Burj
Khalifa is opened. Burj Dubai renamed Burj Khalifa in honor of the current
President of the UAE and Ruler of Abu Dhabi, Sheikh Khalifa bin Zayed al
Nahyan.
3. WORLD RECORDS
At over 828 meters (2,716.5 feet) and
more than 160 stories, Burj Khalifa holds the following records:
• The tallest building in the world
• Tallest free-standing structure in
the world
• The highest number of stories in the
world
• Highest occupied floor in the world
• The highest outdoor observation deck in
the world
• Elevator with the longest travel
distance in the world
• Tallest service elevator in the
world
• Tallest of the Supertall
Not only is Burj Khalifa the world’s
the tallest building, it has also broken two other impressive records: tallest
structure, previously held by the KVLY-TV mast in Blanchard, North Dakota, and
tallest free-standing structure, previously held by Toronto’s CN Tower. The
Chicago-based Council on Tall Buildings and Urban Habitat (CTBUH) has
established 3 criteria to determine what makes a tall building tall. Burj
Khalifa wins by far in all three categories.
a) Height to architectural top
b) Highest occupied floor
c) Height to tip
4. Structural Elements — Elevators, Spire, and More
It is an understatement to say that
Burj Khalifa represents the state-of-the-art in building design. From initial
concept through completion, a combination of several important technological
innovations and innovative structural design methods have resulted in a
the superstructure that is both efficient and robust.
a) Foundation
The superstructure is supported by a
large reinforced concrete mat, which is in turn supported by bored reinforced
concrete piles. The design was based on extensive geotechnical and seismic
studies. The mat is 3.7 meters thick and was constructed in four separate
pours totaling 12,500 cubic meters of concrete. The 1.5-meter diameter x 43
meter long piles represent the largest and longest piles conventionally
available in the region. A high density, low permeability concrete was used in
the foundations, as well as a cathodic protection system under the mat, to
minimize any detrimental effects form corrosive chemicals in local ground
water.
b) Podium
The podium provides a base anchoring
the tower to the ground, allowing on grade access from three different sides to
three different levels of the building. Fully glazed entry pavilions
constructed with a suspended cable-net structure provide separate entries for
the Corporate Suites at B1 and Concourse Levels, the Burj Khalifa residences at
Ground Level and the Armani Hotel at Level 1.
c) Exterior Cladding
The exterior cladding is comprised of
reflective glazing with aluminum and textured stainless steel spandrel panels
and stainless steel vertical tubular fins. Close to 26,000 glass panels, each
individually hand-cut were used in the exterior cladding of Burj Khalifa. Over
300 cladding specialists from China were brought in for the cladding work on
the tower. The cladding system is designed to withstand Dubai's extreme summer
heat, and to further ensure its integrity, a World War II airplane engine was
used for dynamic wind and water testing. The curtain wall of Burj Khalifa is
equivalent to 17 football (soccer) fields or 25 American football fields.
d) Structural System
In addition to its aesthetic
and functional advantages, the spiraling “Y” shaped plan was utilized to shape
the structural core of Burj Khalifa. This design helps to reduce the wind
forces on the tower, as well as to keep the structure simple and foster constructability.
The structural system can be described as a “buttressed core”, and consists of high-performance concrete wall construction. Each of the wings buttresses the
others via a six-sided central core or hexagonal hub. This central core
provides the torsional resistance of the structure, similar to a closed pipe or
axle. Corridor walls extend from the central core to near the end of each wing,
terminating in thickened hammer head walls. These corridor walls and hammerhead
walls behave similarly to the webs and flanges of a beam to resist the wind
shears and moments. Perimeter columns and flat plate floor construction
complete the system. At mechanical floors, outrigger walls are provided to link
the perimeter columns to the interior wall system, allowing the perimeter
columns to participate in the lateral load resistance of the structure; hence,
all of the vertical concrete is utilized to support both gravity and lateral
loads. The result is a tower that is extremely stiff laterally and torsionally.
It is also a very efficient structure in that the gravity load resisting system
has been utilized so as to maximize its use in resisting lateral loads.
As the building spirals in height,
the wings set back to provide many different floor plates. The setbacks are
organized with the tower’s grid, such that the building stepping is
accomplished by aligning columns above with walls below to provide a smooth
load path. As such, the tower does not contain any structural transfers. These
setbacks also have the advantage of providing a different width to the tower
for each differing floor plate. This stepping and shaping of the tower has the
effect of “confusing the wind”: wind vortices never get organized over the
height of the building because at each new tier the wind encounters a different
building shape.
e) Spire
The crowning touch of Burj Khalifa is
its telescopic spire comprised of more than 4,000 tons of structural steel. The
the spire was constructed from inside the building and jacked to its full height of
over 200 meters (700 feet) using a hydraulic pump. In addition to securing Burj
Khalifa's place as the world's tallest structure, the spire is integral to the
the overall design, creating a sense of completion for the landmark. The spire also
houses communications equipment.
f) Mechanical Floors
Seven double-story height mechanical
floors house the equipment that brings Burj Khalifa to life. Distributed around
every 30 stories, the mechanical floors house the electrical sub-stations,
water tanks and pumps, air-handling units, etc, that are essential for the
operation of the tower and the comfort of its occupants.
g) Window Washing Bays
Access for the tower's exterior for
both window washing and façade maintenance is provided by 18 permanently
installed track and fixed telescopic, cradle equipped, building maintenance
units. The track-mounted units are stored in garages, within the structure, and
are not visible when not in use. The manned cradles are capable of accessing
the entire facade from tower top down to level seven. The building maintenance
units jib arms when fully extended will have a maximum reach of 36 meters with
an overall length of approximately 45 meters. When fully retracted, to parked
position, the jib arm length will measure approximately 15 meters. Under normal
conditions, with all building maintenance units in operation, it will take
three to four months to clean the entire exterior facade.
h) Broadcast and Communications Floors
The top four floors have been
reserved for communications and broadcasting. These floors occupy the levels
just below the spire.
i) Mechanical, Electrical & Plumbing
To achieve the greatest efficiencies,
the mechanical, electrical and plumbing services for Burj Khalifa were
developed in coordination during the design phase with the cooperation of the
architect, structural engineer and another consultant.
•The tower's water system
supplies an average of 946,000 liters (250,000 gallons) of water daily
•At peak cooling, Burj Khalifa will
require about 10,000 tons of cooling, equal to the cooling capacity provided by
about 10,000 tons of melting ice
•Dubai's hot, humid climate combined
with the building's cooling requirements creates a significant amount of
condensation. This water is collected and drained in a separate piping system
to a holding tank in the basement car park
•The condensate collection system provides
about 15 million gallons of supplement water per year, equal to about 20
Olympic-sized swimming pools
•The tower's peak electrical demand
is 36mW, equal to about 360,000 100 Watt bulbs operating simultaneously
j) Fire Safety
Fire safety and speed of evacuation
were prime factors in the design of Burj Khalifa. Concrete surrounds all
stairwells and the building service and fireman's elevator will have a capacity
of 5,500 kg and will be the world's tallest service elevator. Since people
can't reasonably be expected to walk down 160 floors, there are pressurized,
air-conditioned refuge areas located approximately every 25 floors.
k) Elevators & Lifts
Burj Khalifa will be home to 57
elevators and 8 escalators The building service/fireman's elevator will have a
the capacity of 5,500 kg and will be the world's tallest service elevator. Burj
Khalifa will be the first mega-high rise in which certain elevators will be
programmed to permit controlled evacuation for certain fire or security events.
Burj Khalifa's Observatory elevators are double-deck cabs with a capacity for
12-14 people per cab. Traveling at 10 meters per second, they will have the
world's longest travel distance from lowest to highest stop.
5. ARCHITECTURE AND
DESIGN
While it is superlative in every
respect, it is the unique design of Burj Khalifa that truly sets it apart. The centerpiece of this new world capital attracted the world's most esteemed
designers to an invited design competition.Ultimately, the honor of designing
the world's tallest tower was awarded the global leader in creating ultra-tall
structures, the Chicago office of Skidmore, Owings & Merrill LLP (SOM) with
Adrian Smith FAIA, RIBA, consulting design Partner. The selected design was
subject to an extensive peer review program to confirm the safety and
effectiveness of the structural systems.
The design of Burj Khalifa is derived
from patterning systems embodied in Islamic architecture. According to the
structural engineer, Bill Baker of SOM, the building's design incorporates
cultural and historical elements particular to the region. The Y-shaped plan is
ideal for residential and hotel usage, with the wings allowing maximum outward
views and inward natural light. The design architect, Adrian Smith, has said the
triple lobed footprint of the building was inspired by the flower Hymenocallis.
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 cross-section of the tower as it
reaches toward the sky. There are 27 terraces in Burj Khalifa. At the top, the
central core emerges and is sculpted to form a finishing spire. A Y-shaped
floor plan maximizes views of the Persian Gulf. Viewed from above or from the
base, the form also evokes the onion domes of Islamic architecture. During the
design process, engineers rotated the building 120 degrees from its original
layout to reduce stress from prevailing winds.
The spire of Burj Khalifa is composed
of more than 4,000 tonnes (4,400 short tons; 3,900 long tons) of structural
steel. The central pinnacle pipe weighing 350 tonnes (390 short tons; 340 long
tons) was constructed from inside the building and jacked to its full height of
over 200 m (660 ft) using a strand jack system. The spire also houses
communications equipment.
More than 1,000 pieces of art will
adorn the interiors of Burj Khalifa,while the residential lobby of Burj Khalifa
will display the work of Jaume Plensa, featuring 196 bronze and brass alloy
cymbals representing the 196 countries of the world. The visitors in this lobby
will be able to hear a distinct timbre as the cymbals, plated with 18-carat
gold, are struck by dripping water, intended to mimic the sound of water
falling on leaves. The exterior cladding of Burj Khalifa consists of 142,000 m2
(1,528,000 sq ft) of reflective glazing, and aluminum and textured stainless
steel spandrel panels with vertical tubular fins. The cladding system is
designed to withstand Dubai's extreme summer temperatures.. Over 26,000 glass
panels were used in the exterior cladding of Burj Khalifa. Over 300 cladding
specialists from China were brought in for the cladding work on the tower.
Also Read:-Introduction compass survey
6. STRUCTURAL SYSTEM DESCRIPTION
The goal of the Burj Dubai Tower is
not simply to be the world's highest building; it's to embody the world's
highest aspirations.The 280 000 m2 (3 000 000 ft2) reinforced concrete
multi-use tower is utilized for retail, a Giorgio Armani Hotel, residential and
office.Designers purposely shaped the structural concrete Burj Dubai—'Y' shaped
in the plan—to reduce the wind forces on the tower, as well as to keep the
structure simple and foster constructability. The structural system can be
described as a 'buttressed' core. Each wing, with its own high-performance
concrete corridor walls and perimeter columns buttresses the others via a
six-sided central core, or hexagonal hub. The result is a tower that is
extremely stiff laterally and torsionally. Skidmore, Owings & Merrill (SOM)
applied a rigorous geometry to the tower that aligned all the common central
core, wall, and column elements.
7. STRUCTURAL ANALYSIS AND DESIGN
The center hexagonal reinforced
concrete core walls provide the torsional resistance of the structure similar
to a closed tube or axle. The center hexagonal walls are buttressed by the wing
walls and hammerhead walls, which behave as the webs and flanges of a beam to
resist the wind shears and moments. Outriggers at the mechanical floors allow
the columns to participate in the lateral load resistance of the structure;
hence, all of the vertical concrete is utilized to support both gravity and
lateral loads. The wall concrete specified strengths ranged from C80 to C60
cube strength and utilized Portland cement and fly ash. Local aggregates were
utilized for the concrete mix design. The C80 concrete for the lower portion of
the structure had a specified Young's elastic modulus of 43 800 N/mm2 (6350 KSI) at 90 days. The wall and column sizes were optimized using virtual
work/LaGrange multiplier methodology, which results in a very efficient
structure. The reinforced concrete structure was designed in accordance with
the requirements of ACI 318-02 Building Code Requirements for Structural
Concrete.
The wall thicknesses and column sizes
were fine-tuned to reduce the effects of creep and shrinkage on the individual
elements which compose the structure. To reduce the effects of differential
column shortening, due to creep, between the perimeter columns and interior
walls, the perimeter columns were sized such that the self-weight gravity
stress on the perimeter columns matched the stress on the interior corridor
walls. The five sets of outriggers, distributed up the building, tie all the
vertical load-carrying elements together, further ensuring uniform gravity
stresses, hence reducing differential creep movements. Since the shrinkage in
concrete occurs more quickly in thinner walls or columns, the perimeter column
the thickness of 600 mm (24 in.) matched the typical corridor wall thickness
(similar volume-to-surface ratios) (Figure 4b) to ensure the columns and walls
will generally shorten at the same rate due to concrete shrinkage.
The top section of the tower consists
of a structural steel spire utilizing a diagonally braced lateral system. The
structural steel spire was designed for gravity, wind, seismic and fatigue in
accordance with the requirements of AISC Load and Resistance Factor Design
Specification for Structural Steel Buildings (1999). The exterior exposed steel
is protected with a flame-applied aluminum
finish.
The structure was analyzed for
gravity (including P-A analysis), wind, and seismic loads using ETABS version
84. The three-dimensional analysis model consisted of the reinforced concrete
walls, link beams, slabs, raft, piles, and the spire structural steel system.
8. WIND ENGINEERING
For a building of this height and
slenderness, wind forces and the resulting motions in the upper levels become
dominant factors in the structural design. An extensive program of wind tunnel
tests and other studies were undertaken (Figure 11). The wind tunnel program
included rigid-model force balance tests, full multi-degree of freedom
aeroelastic model studies, measurements of localized pressures, pedestrian wind
environment studies, and wind climatic studies. Wind tunnel models account for
the cross-wind effects of wind-induced vortex shedding on the building (Figure
12). The aeroelastic and force balance studies used models mostly at 1: 500
scale.
To determine the wind loading on the
the main structure, wind tunnel tests were undertaken early in the design using the
high-frequency force-balance technique. The wind tunnel data were then combined
with the dynamic properties of the tower in order to compute the tower's
dynamic response and the overall effective wind force distributions at full
scale. For the Burj Dubai, the results of the force balance tests were used as
early input for the structural design and detailed shape of the tower and
allowed parametric studies to be undertaken on the effects of varying the
tower's stiffness and mass distribution.
The building has essentially six
important wind directions. The principal wind directions are when the wind is
blowing into the 'nose'/'cutwater' of each of the three wings (Nose A, Nose B,
and Nose C). The other three directions are when the wind blows in between two
wings, termed the 'tail' directions (Tail A, Tail B, and Tail C). It was
noticed that the force spectra for different wind directions showed less
excitation in the important frequency range for winds impacting the pointed or
nose end of a wing (Figure 13) than from the opposite direction (tail). This
was borne in mind when selecting the orientation of the tower relative to the
most frequent strong wind directions for Dubai and the direction of the set
backs.
Several rounds of force balance tests
were undertaken as the geometry of the tower evolved and was refined
architecturally. The three wings set back in a clockwise sequence, with the A-wing setting back first. After each round of wind tunnel testing, the data were
analyzed and the building was reshaped to minimize wind effects and accommodate
unrelated changes in the client's program. In general, the number and spacing
of the setbacks changed as did the shape of the wings. This process resulted in a
substantial reduction in wind forces on the tower by 'confusing' the wind
(Figure 13) by encouraging disorganized vortex shedding over the height of the
tower. Towards the end of design more accurate, aeroelastic model tests were
initiated. An aeroelastic model is flexible in the same manner as the real
building, with properly scaled stiffness, mass, and damping. The aeroelastic
tests were able to model several of the higher translational modes of
vibration. These higher modes dominated the structural response and design of
the tower except at the very base, where the fundamental modes controlled.
Based on the results of the aeroelastic models, the predicted building motions
are within the ISO standard recommended values without the need for auxiliary
damping.
9. FOUNDATIONS AND SITE CONDITIONS
The tower foundations consist of a
pile-supported raft. The solid reinforced concrete raft is 3-7 m (12 ft) thick
and was poured utilizing C50 (cube strength) self-consolidating concrete (SCC).
In addition to the standard cube tests, the raft concrete was field-tested
prior to placement by flow table (Figure 6), L-box, V-box, and temperature. The
raft was constructed in four separate pours (three wings and the center core).
Reinforcement was typically at 300 mm spacing in the raft, and arranged such
that every 10th bar in each direction was omitted, resulting in a series of
'pour enhancement strips' throughout the raft at which 600 mm x 600 mm openings
at regular intervals facilitated access and concrete placement. The tower raft
is 3.7 m (12 ft) thick and therefore, in addition to durability, limiting peak
temperature was an important consideration. The 50 MPa raft mix incorporated
40% fly ash and a water-cement ratio of 0-34. Giant placement test cubes of the
raft concrete, 3.7 m (12 ft) on a side (Figure 7) were test poured to verify
the placement procedures and monitor the concrete temperature rise.
The tower raft is supported by 194
bored cast-in-place piles. The piles are 15 m in diameter and approximately 43
m long, with a design capacity of 3000 tonnes each. The tower pile load test
supported over 6000 tonnes (Figure 9). The C60 (cube strength) SCC concrete
was placed by the tremie method utilizing polymer slurry. The friction piles
are supported in the naturally cemented calcisilt-ite/conglomeritic
calcisiltite formations, developing an ultimate pile skin friction of 250-350
kPa (2-6-3-6 tons/ft2). When the rebar cage was placed in the piles, special
attention was paid to orient the rebar cage such that the raft bottom rebar
could be threaded through the numerous pile rebar cages without interruption,
which greatly simplified the raft construction.
The site geotechnical investigation
consisted of the following phases:
Phase 1: 23 boreholes (three
with pressure meter testing) with depths up to 90 m;
Phase 2: three boreholes drilled
with cross-hole geophysics;
Phase 3: six boreholes (two with
pressure meter testing) with depths up to 60m.
Phase 4: one borehole with
cross-hole and down-hole geophysics; depth = 140 m.
The UK) based on the results of the
geotechnical investigation and the pile load test results. It was determined
the maximum long-term settlement over time would be about a maximum of 80 mm
(3.1 in.). This settlement would be a gradual curvature of the top of grade
over the entire large site. When the construction was at Level 135, the average
foundation settlement was 30 mm (1.2 in.).The groundwater in which the Burj
Dubai substructure is constructed is particularly severe, with chloride
concentrations of up to 4-5% and sulfates of up to 0-6%. The chloride and
sulfate concentrations found in the groundwater are even higher than the
concentrations in sea water. Accordingly, the primary consideration in
designing the piles and raft foundation was durability. The concrete mix for
the piles was a 60 MPa mix based on a triple blend with 25% fly ash, 7% silica
fume, and water: cement ratio of 0-32. The concrete was also designed as fully self-consolidating concrete, incorporating a viscosity-modifying
admixture with a slump flow of 675 ± 75 mm to limit the possibility of defects
during construction.
Owing to the aggressive conditions
present due to the extremely corrosive ground water, a rigorous program of
anti-corrosion measures were required to ensure the durability of the
foundations. Measures implemented included specialized waterproofing systems,
increased concrete cover, the addition of corrosion inhibitors to the concrete
mix, stringent crack control design criteria, and an impressed current cathodic
protection system utilizing titanium mesh.
10. CONCLUSION
More than just the world's tallest
building, Burj Khalifa is an unprecedented example of international
cooperation, a symbolic beacon of progress, and an emblem of the new, dynamic and
prosperous Middle East.It is also tangible proof of Dubai's growing role in a
changing world. In fewer than 30 years, this city has transformed itself from a
regional center to a global one. This success was not based on oil reserves,
but on reserves of human talent, ingenuity and initiative. Burj Khalifa
embodies that vision.. It represents a significant achievement in terms of utilizing
the latest design, materials, and construction technology and methods, in order
to provide an efficient, rational structure to rise to heights never before seen.
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