3. INTRODUCTION
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The tube is the name given to the systems where in order to resist
lateral loads (wind, seismic, etc.) a building is designed to act like a three-
dimensional hollow tube. The system was introduced by Fazlur Rahman Khan
while at Skidmore, Owings and Merrill's (SOM) Chicago office. The first example
of the tube’s use is the 43-story Khan-designed DeWitt-Chestnut Apartment
Building in Chicago, Illinois, completed in 1963.
The system can be constructed using steel, concrete, or composite construction
(the discrete use of both steel and concrete). It can be used for office,
apartment and mixed-use buildings. Most buildings in excess of 40 stories
constructed in the United States since the 1960s are of this structural type.
4. CONCEPT
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The tube system concept is based on the idea that a building can be
designed to resist lateral loads by designing it as a hollow cantilever
perpendicular to the ground.
In the simplest incarnation of the tube, the perimeter of the exterior consists
of closely spaced columns that are tied together with deep beams through
moment connections. This assembly of columns and beams forms a rigid frame
that amounts to a dense and strong structural wall along the exterior of the
building.
This exterior framing is designed sufficiently strong to resist all lateral loads
on the building, thereby allowing the interior of the building to be simply
framed for gravity loads. Interior columns are comparatively few and located at
the core.
The distance between the exterior and the core frames is spanned with
beams or trusses. This maximizes the effectiveness of the perimeter tube by
transferring some of the gravity loads within the structure to it and increases its
ability to resist overturning due to lateral loads.
5. HISTORY
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Since 1963, a new structural system of framed tubes appeared in skyscraper
design and construction.
Fazlur Khan defined the framed tube structure as "a three dimensional space
structure composed of three, four, or possibly more frames, braced frames, or
shear walls, joined at or near their edges to form a vertical tube-like structural
system capable of resisting lateral forces in any direction by cantilevering from
the foundation."Closely spaced interconnected exterior columns form the tube.
Horizontal loads, for example wind, are supported by the structure as a whole.
About half the exterior surface is available for windows. Framed tubes allow
fewer interior columns, and so create more usable floor space. Where larger
openings like garage doors are required, the tube frame must be interrupted,
with transfer girders used to maintain structural integrity.
6. The first building to apply the tube-frame construction was the DeWitt-
Chestnut apartment building which Khan designed(1963) and was completed in
Chicago by 1965. This laid the foundations for the tube structures of many
other later skyscrapers, including his own John Hancock Center and Willis
Tower, and can been seen in the construction of the World Trade Center,
Petronas Towers, Jin Mao Building, and most other supertall skyscrapers since
the 1960s. The strong influence of tube structure design is also evident in the
construction of the current tallest skyscraper, the Burj Khalifa.
Contd…..
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12. FRAMED TUBE SYSTEM
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This is the simplest incarnation of the tube. Closely spaced
perimeter columns interconnected by beams.
It can take a variety of floor plan shapes from square and
rectangular, circular. This design was first used in Chicago's
DeWitt-Chestnut apartment building, designed by Khan and
completed in 1965, but the most notable examples are the Aon
Center and the destroyed World Trade Center towers.
13. FRAMED TUBE SYSTEM
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• Closely spaced perimeter columns interconnected by
deep spandrels.
• Whole building works as a huge vertical cantilever to
resist overturning moments.
• Efficient system to provide lateral resistance with or
without interior columns.
• Exterior tube carries all the lateral loading.
• Gravity loading is shared between the tube and the
interior columns or walls, if they exist.
14. SHEAR LAG :-
(a) (b)
• If the tube loaded on side AB, then the whole frames AB and CD are
called ‘Flange frames’ and the frames AD and BC are called ‘Web
frame’
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Cont…
15. • The forces in the web frame are growing smaller toward the
center linearly instead in Fig(b) this phenomenon is called Shear
lag.
• The ratio of the stress at the center column to the stress at the
corner column is defined as ‘Shear-lag factor’.
• Stress distribution of the flange and web column - opposite sides
of the neutral axis are subjected to tensile and compressive forces
- under lateral load - Fig. (b)
• The prime action is the flexibility of the spandrel beams that
produces a shear lag that will increases the stresses in the corner
column and reduces those in the inner columns of both the flange
panels AB and DC and the web panels AD and BC
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Cont…
16. TUBE IN A TUBE SYSTEM
• An outer framed tube together with an internal
elevator and service core.
• The outer and inner tubes act jointly in resisting both
gravity and lateral loading in steel-framed buildings.
• More effective in high-rise structure because the
bending and transverse shears are supported three-
dimensionally at the flange and web surface in the
structure.
• The analysis of tube structures has to be based on
three-dimensional analysis using finite element.
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17. Proportioning:
• 30m minimum floor dimension
• Centrally stability core around lifts/stairs, moment
frame around perimeter
• 30 to 60 floor, 100 to 160m height
• Clear floor plates, but wide perimeter columns and
deep perimeter beam constrains view
• Traditionally 2 or 3 zone elevator arrangement, but
would benefit from optimization using double decks
or sky lobbies.
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Cont…
18. Behavior of Tube in Tube Tall Building
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(a) Deform shape of frame;
(b) Deform shape of shear wall;
(c) Deform shape of composite structure
Cont…
• Respond as a unit to lateral forces
• The reaction to wind is similar to that of a
frame and shear wall structure
• The wall deflects in a flexural mode with
concavity downwind and maximum slope at
the top, while the frame deflect in a shear
mode with concavity upwind and maximum
slope at the base
• Composite structure - flexural profile in the
lower part and shear profile in the upper
part.
• The axial forces cause the wall to restrain the
frame near the base and the frames to
restrain the wall at the top
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• The deflection & wall moment curve indicate the reversal in curvature with a point
of inflexion, above which the wall moment is opposite in sense to that in a free
cantilever (fig-a & b)
• Fig-c - The shear is uniform over the height of the frame, except near the base
where it reduces to a negligible amount
• At the top, (where the external shear is zero), the frame is subjected to a significant
positive shear - balanced by an equal negative shear at top of the wall, with a
corresponding concentrated interaction force acting between the frame and the
wall.
Cont… (a) (b) (c)
20. Advantages:
• The wind- resisting system located on the perimeter of the building
– more resistance to overturning moments.
• Core framing leads to a significant gain in rentable space.
• Identical framing for all which are no subjected to varying internal
forces due to lateral loads.
• From a practical point of view, the final analysis and design of the
tube can proceed unaffected by the lengthy process of resolving
detail layout and service requirements in the core area.
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Cont…
21. BUNDLED TUBE
• Instead of one tube, a building consists of several tubes tied
together to resist the lateral forces. Such buildings have interior
columns along the perimeters of the tubes when they fall within
the building envelope. Notable examples include Willis Tower and
One Magnificent Mile.
• The bundle tube design was not only highly efficient in economic
terms, but it was also "innovative in its potential for versatile
formulation of architectural space. Efficient towers no longer had
to be box-like; the tube-units could take on various shapes and
could be bundled together in different sorts of groupings." The
bundled tube structure meant that "buildings no longer need be
boxlike in appearance they could become sculpture."
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22. • It is a cluster of individual tubes connected together to act
as a single unit
• Maintain a reasonable slenderness (i.e., height-to-width)
ratio – Neither excessively flexible and nor sway too much
• Cross walls or cross frames – increases three-dimensional
response of the structure.
• The 110-story Sears Tower completed in 1974 was the first
bundled tube structure in which nine steel framed tubes
are bundled at the base
• Individual tubes could be of different shapes, such as
rectangular, triangular or hexagonal as is demonstrated by
this building
Cont…
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24. • Also known as ‘Trussed Tube’ or ‘Exterior Diagonal-tube System’ -
utilized for greater heights, and allows larger spacing between the
columns
• Steel buildings-steel diagonals/trusses used
• Reinforced concrete buildings-diagonals are created by filling the
window openings by reinforced concrete shear walls -diagonal bracing
• Braced tube structures are lateral load-resisting systems- Located at the
building perimeters made the structural systems for tall buildings much
more efficient and economical.
• The most notable examples are the John Hancock Center, the Citigroup
Center, and the Bank of China Tower.
BRACED TUBE SYSTEM
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25. Behavior under Gravity loading:-
• (a) - Intermediate columns will displace downward by more than
corresponding points on the diagonal- controlled by the vertical
displacement of the less highly stressed corner columns.
• (b) - Downward forces on each diagonal are carried at its ends by the
corner columns - compressive forces are increased at each intersection with
a diagonal = equalization of the stresses in the intermediate and corner
columns.
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Cont…
26. Behavior under lateral loading:-
a) If the diagonals are initially disconnected from the intermediate columns, the columns and
diagonals of the face will be in tension while the spandrels are in compression .
• Because of the shear lag effect the intermediate columns will now be less highly stressed than
the corner columns. the connection points on the diagonals will be displaced upward by more
than the corresponding points on the unconnected intermediate columns.
b) If the diagonals and intermediate columns are connected together, iterative vertical forces will
be mobilized
• These upward forces cause an increase in tension in the intermediate columns
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27. Building Year Stories
(Height/Width)
Structural
System
Steel Usage
in psf
Empire State
Building, NY
1931 102 (9.3) Braced Rigid
Frame John
42.2
Hancock Center,
Chicago
1968 100 (7.9) Braced Tube 29.7
World Trade
Center(Demolished),
NY
1972 110 (6.9) Framed Tube 37.0
Sears Tower, Chicago 1974 109 (6.4) Bundled Tube 33.0
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28. Types Material /
Configurati
on
Efficient
Height
Limit
Advantages Disadvantages Building Examples
Framed Tube
Steel 80
Efficiently resists lateral
loads by locating lateral
systems at the building
perimeter.
Shear lag hinders true
tubular behavior. Narrow
column spacing obstructs
the view.
Aon Center
(Chicago, USA, 83
stories, 346 m)
Concrete 60 Water Tower Place
(Chicago, USA, 74
stories, 262 m)
Braced Tube
Steel 100 (With
Interior
Columns) –
150
(Without
Interior
Columns)
Efficiently resists lateral shear
by axial forces in the diagonal
members. Wider column
spacing possible compared
with framed tubes. Reduced
shear lag.
Bracings obstruct the
view.
John Hancock
Center (Chicago,
USA, 100 stories
344 m)
Concrete 100 Onterie Center
(Chicago, 58
stories, 174 m),
780 Third Avenue
(New York, USA, 50
stories, 174 m)
Comparison of Tube Systems
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29. Types Material /
Configuration
Efficient
Height
Limit
Advantages Disadvantages Building Examples
Bundled Tube
Steel 110
Reduced shear lag.
Interior planning
limitations due to the
bundled tube
configuration.
Sears Tower
(Chicago, USA, 108
stories, 442 m)
Concrete 110 Carnegie Hall Tower
(New York, USA, 62
stories, 230.7 m)
Tube in Tube
Ext. Framed
Tube (Steel or
Concrete) + Int.
Core Tube
(Steel or
Concrete)
80 Effectively resists lateral loads
by producing interior shear
core - exterior framed tube
interacting system.
Interior planning
limitations due to shear
core.
181 West Madison
Street (Chicago,
USA, 50 stories, 207
m)
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30. REFERENCES
• Mir M.Ali and Kyoung Sun Moon “Structural
Developments in Tall Buildings: Current Trends and
Future Prospects”
• en.wikipedia.org
• Kyoung Sun Moon “Material-Saving Design Strategies for
Tall Building Structures”
• Text book- Engineering Architecture the vision of Fazlur R. Khan by
Yasmin Sabina Khan
• sefindia.org
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