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1 Composite Construction 1 Composite Construction

1 Composite Construction - PowerPoint Presentation

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1 Composite Construction - PPT Presentation

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

concrete composite construction steel composite concrete steel construction beams shear section slab resistance columns structures beam loads load column

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Slide1

1

Composite Construction

Introduction to composite construction of buildingsSlide2

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

Concrete provides Protection

against corrosion and fire

Steel bring ductility into the structureSlide3

3

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

4

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

5

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

6

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

7

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

8

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

9

The Various types of composite BeamsSlide10

10

Shear ConnectorsThese connectors are designed toTransmit longitudinal shear along the

interface

prevent separation of steel beam and concrete slab at the interfaceSlide11

11

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

12

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

13

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

14

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

15

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

16

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

19

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

20

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

21

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

22

Joints

Example of vertical shear transfer between beam and columnSlide23

23

Aspects for using composite structures:

Architectural

Economical

Functionality

Service and Flexibility

AssemblySlide24

24

Aspects for using composite structures

Architectural:

Longer spans

Thinner slabs

More slender column

More generous opportunities for designSlide25

25

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

26

Aspects for using composite structures

Functionality:

Fire protection by using principles of reinforced concrete in which the concrete protects the steelSlide27

27

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

28

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

29

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

30

Construction methods

Composite Construction

comparing these two methods a combination of both presents the most economic way

+

higher bearing capacity

+

higher stiffness

+

plastic redistributionSlide31

31

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

32

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

33

Examples

Millennium Tower

(Vienna - Austria)

Total time of erection: 8 month

max. speed 2 to 2.5 storeys per week!Slide34

34

Examples

Parking deck “DEZ”

(Innsbruck - Austria)

Erection of composite columns over 2 storeys

Assembly of prefabricated concrete slabsSlide35

35

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)