Transcript tube - EnggRoom

TUBE STRUCTURES
Faculty,
Prof. V. R. SHAH
Mrs. AANAL SHAH
Mrs. DHARA SHAH
Prepared by,
VASANT BUTANI(SD 0209)
CONTENT
•
•
•
•
•
ITRODUCTION
CONCEPT
HISTORY
TYPES
COMPARISON
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 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.
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.
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.
Contd…..
The first building to apply the tube-frame construction was the DeWittChestnut 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.
DeWitt-Chestnut apartment
building, Chicago 1965
John Hancock Center 1969
World Trade Center, 1987
Petronas Towers, 1998
Jin Mao Tower, Shanghai
1998
Burj Khalifa, Dubai
2010
IN 1969, FAZLUR KHAN STRUCTURAL SYSTEM CLASSIFIED
AS BELOW AS PER THE HEIGHT:
TYPES
1) Framed tube system
2) Tube -in a tube system
3) Bundled tube system
4) Braced tube system
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.
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.
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’
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
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.
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.
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
Cont…
(a)
(b)
(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.
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.
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."
Cont…
• It is a cluster of individual tubes connected together to
act as a single unit
• Maintain a reasonable slenderness (i.e., height-towidth) ratio – Neither excessively flexible and nor sway
too much
• Cross walls or cross frames – increases threedimensional 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
Diagrammatic view of the bundled tube
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.
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.
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
Building
Year
Stories
Structural
(Height/Width) 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(Demolishe
d), NY
1972
110 (6.9)
Framed Tube
37.0
Sears Tower,
Chicago
1974
109 (6.4)
Bundled Tube
33.0
Comparison of Tube Systems
Types
Material /
Configura
tion
Steel
Efficient
Height
Limit
Concrete
60
Steel
100 (With
Interior
Columns) –
150
(Without
Interior
Columns)
100
Concrete
Disadvantages
80
Framed
Tube
Braced Tube
Advantages
Efficiently resists lateral
loads by locating lateral
systems at the building
perimeter.
Shear lag hinders true
tubular behavior.
Narrow column spacing
obstructs the view.
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.
Building
Examples
Aon Center
(Chicago, USA,
83 stories, 346
m)
Water Tower
Place (Chicago,
USA, 74 stories,
262 m)
John Hancock
Center (Chicago,
USA, 100 stories
344 m)
Onterie Center
(Chicago, 58
stories, 174 m),
780 Third Avenue
(New York, USA,
50 stories, 174
m)
Types
Material /
Configuratio
n
Efficient
Height
Limit
Steel
110
Bundled
Tube
Tube in Tube
Advantages
Reduced shear lag.
Concrete
110
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.
Disadvantages
Interior planning
limitations due to the
bundled tube
configuration.
Interior planning
limitations due to shear
core.
Building
Examples
Sears Tower
(Chicago, USA,
108 stories, 442
m)
Carnegie Hall
Tower (New York,
USA, 62 stories,
230.7 m)
181 West Madison
Street (Chicago,
USA, 50 stories,
207 m)
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