TUBE STRUCTURES

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TUBE STRUCTURES
Prepared by, VASANT BUTANI(SD 0209)
Faculty, Prof. V. R. SHAH Mrs. AANAL SHAH Mrs.
DHARA SHAH
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CONTENT

• ITRODUCTION
• CONCEPT
• HISTORY
• TYPES
• COMPARISON

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INTRODUCTION
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
tubes 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.
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CONCEPT

• 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.

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HISTORY
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.
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Contd..
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.
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DeWitt-Chestnut apartment building, Chicago 1965
John Hancock Center 1969
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World Trade Center, 1987
Petronas Towers, 1998
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Jin Mao Tower, Shanghai 1998
Burj Khalifa, Dubai 2010
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IN 1969, FAZLUR KHAN STRUCTURAL SYSTEM CLASSIFIED
AS BELOW AS PER THE HEIGHT
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TYPES

• Framed tube system
• Tube -in a tube system
• Bundled tube system
• Braced tube system

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FRAMED TUBE SYSTEM
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.
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FRAMED TUBE SYSTEM

• 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.

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Cont

• 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

• 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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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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Cont

• 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

• Behavior of Tube in Tube Tall Building

• 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

(a) Deform shape of frame (b) Deform shape of
shear wall (c) Deform shape of composite
structure
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Cont
(b)
(a)
(c)

• 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.

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Cont

• 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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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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Cont

• 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

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Diagrammatic view of the bundled tube
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BRACED TUBE SYSTEM

• 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.

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Cont

• 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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• 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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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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Comparison of Tube Systems
Types Material / Configuration 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)
Framed Tube Concrete 60 Efficiently resists lateral loads by locating lateral systems at the building perimeter. Shear lag hinders true tubular behavior. Narrow column spacing obstructs the view. 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)
Braced Tube Concrete 100 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. Onterie Center (Chicago, 58 stories, 174 m), 780 Third Avenue (New York, USA, 50 stories, 174 m)
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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)
Bundled Tube Concrete 110 Reduced shear lag. Interior planning limitations due to the bundled tube configuration. 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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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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