Introduction to composite construction of buildings 2 General These two materials complete one another Steel and concrete Concrete is efficient in compression and steel in tension Concrete encasement restrain steel against buckling ID: 257406
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Composite Construction
Introduction to composite construction of buildingsSlide2
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General
These two materials complete one another:
Steel
and concrete
Concrete is efficient in compression and steel in tension
Concrete encasement restrain steel against buckling
Concrete provides Protection
against corrosion and fire
Steel bring ductility into the structureSlide3
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Composite construction refers to any members composed of more than one material. The parts of these composite members are rigidly connected such that no relative movement can occur.
The main composite elements in buildings are
1.Steel Concrete Composite Beam
2.Composite Slab
3.Composite
Columnn
Slide4
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Steel Concrete Composite Beam
Composite beams are normally hot rolled or fabricated steel sections that act compositely with the slab. The composite interaction is achieved by the attachment of shear connectors to the top flange of the beam. These connectors generally take the form of headed studs.Slide5
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The composite action increases the load carrying capacity and stiffness of the beam by factors of up to 2 and 3.5 respectively.
It is normally designed to be
unpropped
during construction
, and must be sized to support the self-weight of the slab, and other construction loads, in their non-composite state. Slide6
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size of the steel section is governed by serviceability considerations because composite beams tend to be used for long span applicationsCheck that beam deflections during construction will not lead to significant additional
concrete loads (due to ponding) that have not been allowed for
in the
design
T
he bending resistance of the section is normally evaluated using ‘plastic’ principlesSlide7
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The plastic moment resistance is calculated using idealized rectangular stress Blocks.
It
is assumed that
stresses of
fyd and 0.85 fcd
can be achieved in the steel and concrete respectivelySlide8
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Composite beams are generally shallower (for any given span and loading) than non-composite beams, and they are used commonly in long span applications.Consequently, deflections are often
critical.Slide9
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The Various types of composite BeamsSlide10
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Shear ConnectorsThese connectors are designed toTransmit longitudinal shear along the
interface
prevent separation of steel beam and concrete slab at the interfaceSlide11
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most common type of shear connector used in composite beams for buildings is a 19 mm diameter by either 100 mm or 125 mm long welded stud.Slide12
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The property of shear connector most relevant to design is the relation-ship between the shear force transmitted,
P, and the slip at the interface, s This load-slip curve should ideally be found
from tests on composite beams
.Slide13
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Composite slabs consist of profiled steel decking with an in-situ reinforced concrete topping. The decking(profiled steel sheeting)
not only acts as
permanent formwork
to the concrete, but also provides sufficient shear bond with the concrete so that, when the concrete has gained strength, the two materials act together compositely
span between 3 m and 4.5 m onto supporting beams or wallsSlide14
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If the slab is unpropped during construction, the decking alone resists the selfweight of the wet concrete and construction loads. Subsequent loads are applied to the composite section.
If
the slab is propped, all of the loads have to
be resisted
by the composite section.
are usually designed as simply supported members in the normal conditionSlide15
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Profiled steel sheeting
yield
strengths ranging from 235 N/mm
2
to at least 460 N/mm
2 depths ranging from 45 mm to over 200 mm
.8 mm and 1.5 mm thickThe various shapes provide Interlock between steel and concrete
frictional
mechanicalSlide16
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decking may also be used to stabilise the beams against lateral torsional buckling during construction.
stabilise
the building as a whole by
acting as
a diaphragm to transfer wind loads to the walls and columns
temporary construction load usually governs the choice of decking profileSlide17
17Slide18
COMPOSITE COLUMNS
18A steel-concrete composite column is a compression member, comprising either a concrete encased hot-rolled steel section or a concrete filled tubular section of hot-rolled steel.Slide19
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The presence of the concrete is allowed for in two ways. protection from fireIt is assumed to Resist a small axial load to reduce the effective slenderness of the steel member, which increases its resistance to axial load.
The bending stiffness of steel columns of H-or I-section is much greater in the plane of the web (‘major-axis bending’) than in a plane parallel to the flanges (‘minor-axis bending’).Slide20
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There is no requirement to provide additional reinforcing steel for composite concrete filled tubular sections.The ductility performance of circular type of columns is significantly better than rectangular types.
corrosion protection is provided by concrete to steel sections in encased columnsSlide21
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The plastic compression resistance of a composite cross-section represents the maximum load that can be applied to a short composite column.While local buckling of the steel sections may be eliminated, the reduction in the compression resistance of the composite column due to overall buckling should definitely be allowed for.Slide22
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Joints
Example of vertical shear transfer between beam and columnSlide23
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Aspects for using composite structures:
Architectural
Economical
Functionality
Service and Flexibility
AssemblySlide24
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Aspects for using composite structures
Architectural:
Longer spans
Thinner slabs
More slender column
More generous opportunities for designSlide25
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Aspects for using composite structures
Economical:
Reduction of height reduces the total of the building --> saving area of cladding
Longer spans with the same height
--> column free rooms
Additional storeys with the same total height of building
Quicker time of erection:
Saving costs, earlier completion of the building
Lower financing costs
Ready for use earlier thus increasing rental incomeSlide26
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Aspects for using composite structures
Functionality:
Fire protection by using principles of reinforced concrete in which the concrete protects the steelSlide27
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Aspects for using composite structures
Service and building flexibility:
Adaptable structures
Modification during the life of the building
Modify services without violating the privacy of other occupants
Accommodation of service facilities
in the ceiling
within a false floor
in a coffer box running along the wallsSlide28
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Aspects for using composite structures
Assembly:
Working platforms of steel decking
Permanent shuttering
Reinforcement of profiled steel sheetings
Speed and simplicity of construction
Quality controlled products ensure greater accuracySlide29
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Construction methods
Traditionally two counteracting methods of construction could be observed both connected with special advantages but also disadvantages worth mentioning.
Conventional concrete construction method
Construction in steel
+
freedom of form and shapes
+
easy to handle
+
thermal resistance
-
time-consuming shuttering
-
sensitive on tensile forces
+
high ratio between bearing capacity and weight
+
prefabrication
+
high accuracy
-
low fire resistance
-
need of higher educated personalSlide30
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Construction methods
Composite Construction
comparing these two methods a combination of both presents the most economic way
+
higher bearing capacity
+
higher stiffness
+
plastic redistributionSlide31
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Examples
Millennium Tower
(Vienna - Austria)
55 storeys
Total height 202 m
Total ground floor 38000 m2
Capital expenditure about 145 million Euro
Time of erection: 8 monthsSlide32
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Examples
Millennium Tower
(Vienna - Austria)
Composite columns
Concrete core
Composite Slim floor beams
Concrete slab
42,3 m
Composite frame
42,3 m
33,05 mSlide33
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Examples
Millennium Tower
(Vienna - Austria)
Total time of erection: 8 month
max. speed 2 to 2.5 storeys per week!Slide34
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Examples
Parking deck “DEZ”
(Innsbruck - Austria)
Erection of composite columns over 2 storeys
Assembly of prefabricated concrete slabsSlide35
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Examples
Parking deck “DEZ”
(Innsbruck - Austria)
4 storeys
Ground dimensions 60 x 30 m
Max. span length 10.58 m with
26 cm slim floor slab (= l/40)