151905098-tall
TRANSCRIPT
TALL STRUCTURES
INTRODUCTION
Tall Structures has been fascination mankind since early ages.
Human beings urge to stand tall which has been expressed through
construction of tall monuments, high places of worship in the beginning.
Further the invention of elevators, air-conditioning systems etc., have
made the living in tall buildings comfortable.. Emergence of new efficient
structural systems, high strength materials, construction technology has
made the dream of scaling the sky realistic for nearly 0.7 kms at present.
Scarcity of living space has prompted engineers to conceptualize vertical
cities in this century.
DEFINITION:
The tallness of the building is relative and cannot be defined is
absolute terms either in relation to height or the number of stories. But
from a structural engineers point of view the tall building can be defined
as one that, by virtue of its height, is affected by lateral forces due to wind
or earthquake or both to an extent that they play an important role in the
structural design.
‘A building whose height creates different conditions in the
design, construction and use than those that exists in common buildings
of a certain region and period’ by the council of Tall Buildings and habitat.
WHY DO WE NEED A TALL BUILDING?
Tall structures have fascinated mankind since
They stand as a mark of prestige and civilization.
They serve as landmark in the global picture.
The increasing demand for shelter is met without encroaching
on the agricultural land.
FACTORS AFFECTING GROWTH, HEIGHT AND
STRUCTURED FORM OF A TALL BUILDING:
State of Art of Service Systems.
Availability of Material.
Construction Technology.
Building Name Location Year Height in
metres Material Use
Pyramids Egypt 2500 B.C. 147 Stone Tomb
Singer USA 1907 187 Steel Office
Metropolitan Tower USA 1909 206 Steel Office
Woolworth USA 1913 242 Steel Office
Chrysler USA 1929 319 Steel Office
Empire State Building USA 1931 381 Steel Office
World trade Centre USA 1972 412 Steel Office
Sears Towers USA 1973 442 Steel Office
Petronas Towers Malaysia 1996 452 Mixed Multipurpose
Tapei Towers Taiwan 2005 515 Mixed Multipurpose
CHRONOLOGY OF INCREASE IN HEIGHT OF TALL BUILDINGS:
Building Name Location Year Height in metres Material
Tapei Towers Taiwan 2005 515 Mixed
Petronas Towers 1 Malaysia 1996 452 Mixed
Petronas Towers 2 Malaysia 1996 452 Mixed
Sears Towers USA 1973 442 Steel
World trade Centre 1 USA 1972 417 Steel
World trade Centre 2 USA 1972 415 Steel
Empire State Building USA 1931 381 Steel
Central Plaza Hong kong 1992 374 Concrete
Bank of China Tower Hong Kong 1989 369 Mixed
Amoco Building USA 1973 346 Steel
TEN TALL BUILDINGS IN THE WORLD
IMPACT OF TALL BUILDINGS ON MANKIND:
Living on horizontal cities has a different effect on the people
when compared to their life in tall buildings. Many are the benefits that
can be listed out as follows
Brightness is ensured because of the height.
Fresh air is available.
Dust free clean environment is possible.
Privacy is ensured.
Noise pollution is made less.
Land is used in a better way.
A landmark is created.
Stands as a mark of respect (Prestige and Progress of the country)
Generates interest in tourism to the place.
It has also been reported that there are many practical and
psychological problems in living of high rise structures. They are
mentioned below:
Space and operation of lifts cost problems.
Safety of children is less.
Does not provide a garden for residence of top floors.
Reduces family interaction.
The vandalism and crime rate increases.
Fear of failure of the structure is implicit.
Elderly people find it inconvenient to live.
Increases traffic problem in the nearby area.
Increase in land value.
Children feel isolated and their study performance is found to be
affected.
Due to restricted social space, melancholy is created.
COMPONENTS OF A TALL STRUCTURE:
Structural systems
Mechanical systems
Electrical systems
Partition walls and claddings
Foundation
STRUCTURAL SYSTEMS
Systems for resistingVertical Loads Horizontal Loads
Systems for resisting
VERTICAL FRAMING SYSTEMS:
These systems function primarily to carry vertical loads. In short
they can be called as vertical load transfer systems which may be either
columns or bearing walls or hangers or suspended systems.
LATERAL LOAD RESISTING SYSTEMS:
Rigid Frames
Braced Frames
Shear Walls
Wall frame Structure
Tubular Structure
Tube in Tube buildings
Outrigger – Braced Structure
RIGID FRAME STRUCTURES:
Rigid frame structures consist of columns and girders
joined by moment resisting connections. The lateral stiffness of
a rigid frame depends on the bending stiffness of the columns,
girders and connections in the plane of the bent. The rigid
frames principal advantage is its open rectangular
arrangement which allows freedom of planning and easy fitting
of doors and windows.
RIGID FRAME STRUCTURES Contd.,
If used as the only source of lateral resistance in a building in
its only typical 6m x 9m bay size, rigid framing is economic only for
buildings up to 25 stories. Above 25 stories the relatively high lateral
flexibility of the frame cells are uneconomically large members in order
to control the drift.
Deformations of a moment resisting frame under lateral
load
The point of contra flexure is normally located near the midheight of the
columns and midspan of the beams.
The connections in steel moment resisting frames are important design
elements. Joint rotation can account for a significant portion of the lateral
sway. The strength and ductility of the connections are also important
considerations especially for frames designed to resist seismic loads.
APPLICATIONS:
Moment resisting frames are normally efficient for buildings up to 30
storeys in height. The lack of efficiency for taller buildings is due to the moment
resistance derived primarily through flexure of its members.
EXAMPLE: World trade centre, Osaka, Japan 252 m high, 55 storeys.
BRACED FRAME:
Rigid frames are not efficient for buildings taller than 30 storeys
because the shear racking component of deflection due to the bending of
columns and girders causes the drift to be too large. The braced frame
attempts to improve upon the efficiency of a rigid frame by virtually eliminating
the bending of columns and girders. This is achieved by adding the web
members such as diagonals or braces. The horizontal shear is now primarily
absorbed by the web and not by the columns. The webs carry the lateral shear
predominantly by the horizontal component of axial action allowing for nearly a
pure cantilever behavior.
Behavior:
In simple terms, braced frames may be considered as cantilevered
vertical trusses resisting lateral loads primarily through the axial stiffness of the
columns and braces. The columns act as the chords in resisting the overturn
moment, with tension in the windward column and compression in the leeward
column. The diagonals and girders work as the web members in resisting the
horizontal shear with diagonals in axial compression or tension depending upon
their direction of inclination. They undergo bending when the braces are
eccentrically connected to them because the lateral loads on the building is
reversible, braces are subjected to turn, to both compression and tension.
BEHAVIOR OF BRACED FRAMES
TYPES OF BRACES
ECCENTRIC BRACESCONCENTRIC BRACES
The braced frames can be grouped under above two categories
depending upon their ductility characteristics. In concentric braces, the axes of
all members, that is, columns, beams and braces intersect at a common point
such that the member forces are axial. The eccentric braces utilize offsets to
deliberately introduce flexure and shear into framing beams to increase ductility
CONCENTRIC BRACES
ECCENTRIC BRACES
SHEAR WALL STRUCTURE:
Concrete and masonry continuous vertical walls may serve both
architecturally as partitions and structurally to carry gravity and lateral loading.
This very high plane stiffness and strength makes them ideally suited for bracing
tall buildings. In a shear wall structure, such walls are entirely responsible for the
lateral load resistance of the building. They act as vertical cantilevers in the form
of separate planar walls and as nonplanar assemblies of connected walls around
elevators, stairs and service shafts. They are much stiffer horizontally than rigid
frames, shear wall structures can be economical up to about 35 stories.
SHEAR WALL STRUCTURE
WALL FRAME STRUCTURES:
When shear walls are combined with rigid frames the walls, which tend
to deflect in a flexural configuration, and the frames, which tend to deflect in a
shear mode, are constrained to adopt a common deflected shape by the horizontal
rigidity of the girders and slabs. As a consequence the walls and frames interact
horizontally, especially at the top, to produce a stiffer and stronger structure. The
interacting wall – frame combination is appropriate for buildings in the 40 – 60 storey
range, well beyond that of rigid frames of shear walls alone.
TUBULAR STRUCTURE:
The lateral resistance of framed tube structures is provided by very
stiff moment resisting frames that form a ‘tube’ around the perimeter of the
building. The frames consist of closely spaced columns, 6 – 12 ft ( 2 – 4 m)
between centers, joined by deep spandrel girders. Although the tube carries all
the lateral loading the gravity loading is shared between the tube and interior
columns or walls. When lateral load acts, the perimeter frames aligned in the
direction of loading act as the webs of the massive tube cantilever and those
normal to the direction of the loading act as the flanges. The tube is suitable
for both steel and reinforced concrete construction and has been used for
buildings ranging from 40 – 100 storeys.
TUBULAR STRUCTURE
TUBE IN TUBE STRUCTURE:
This variation of the framed tube consists of an outer framed
tube the hull together with an internal elevator and service core. The hull
and core act jointly in resisting both gravity and lateral loading. In a steel
structure the core may consist of braced frames, whereas in a concrete
structure it would consist of an assembly of shear walls. To some extent
the outer framed tube and the inner core interact horizontally as the
shear and flexural components of a wall frame structure with the benefit
of increased lateral stiffness.
TUBE IN TUBE STRUCTURE
OUTRIGGER BRACED STRUCTURE:
The efficient structural form consists of a central core, comprising
either braced frames or shear walls, with horizontal cantilever “ outrigger
trusses “ or girders connecting the core to the outer columns. When the
structure is loaded horizontally, vertical plane rotations of the core are
restrained by the outriggers through tension in the windward columns and
compression in the leeward columns. Outrigger-braced structures have been
used for buildings from 40 – 70 storeys high, but the system should be
effective and efficient for much greater depths.
OUTRIGGER BRACED STRUCTURE