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Composite structure of steel and concrete has been explained under this ppt with examples, type of structural members, advantages and comparison with other structures like R.C.C structure and Steel structures.
A composite member is defined as consisting of a rolled or a built-up structural steel shape that is either filled with concrete, encased by reinforced concrete or structurally connected to a reinforced concrete slab. Composite members are constructed such that the structural steel shape and the concrete act together to resist axial compression and /or bending.
a stress factor a = 0.87 fy/0.36(fck)cu is applied to convert the concrete section into steel.
Ability to cover large column free area in buildings and longer span for bridges/flyovers. This leads to more usable space. Reduced beam depth reduces the story height and consequently the cost of cladding in a building and lowers the cost of embankment in a flyover. More use of a material i.e. steel, which is durable, fully recyclable on replacement and environment friendly. Reductions in overall weight of structure and thereby reduction in foundation costs.
The decking 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.
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.
Shear forces in secondary beams are increased by average 83.3% in steel structure and reduced by average 10 % in composite structure as compared to R.C.C. framed structure while in main beams shear forces are increased by average 131% in steel structure and reduced by average 100 % in composite structure as compared to R.C.C. framed structure. Bending moments in secondary beams are increased by average 83.3% in steel structure and reduced by average 48 % in composite structure as compared to R.C.C. framed structure while in main beams bending moments are increased 131% in steel structure and increased by average 117 % in composite structure as compared to R.C.C. framed structure.
Composite construction or Composite Structure/Frame
Syed Abdul Rahman
• The two complementary materials, structural steel and
reinforced concrete, are introduced.
• To explain the composite action of the two different
materials and to show how the structural members are
used, particularly in building construction.
• The use of composite construction for buildings is
• Its Advantages and Disadvantages are also illustrated.
The most important and most frequently encountered
combination of construction materials is that of steel and
concrete, with applications in multi-storey commercial
buildings and factories, as well as in bridges.
Composite construction refers to two load-carrying
structural members that are integrally connected and
deflect as a single unit.
This has become a standard type of construction in high
rise buildings selected by many Architects , Engineers
Composite floor systems are considered by many to be
the highest quality type of construction.
These essentially different materials are completely
compatible and complementary to each other.
Almost the same thermal expansion;
An ideal combination of strengths with the concrete
efficient in compression and the steel in tension;
Concrete also gives corrosion protection and thermal
insulation to the steel at elevated temperatures.
The Indian Code of Practice for Composite
Construction in Structural Steel and Concrete (IS:
11384 – 1985)
The Indian Code of Practice for Composite
Construction in Structural Steel and Concrete
(IS: 11384 – 1985)
• The maximum strain in concrete at outermost compression member is
taken as 0.0035 in bending.
• The total compressive force in concrete is given by
and this acts at a depth of 0.42 xu, not exceeding ds.
• The stress strain curve for steel section and concrete are as per IS: 456-
• A stress factor is applied to convert the
concrete section into steel.
Fcc = 0.36 (fck) bXu
a = 0.87 fy/0.36(fck)
Composite construction used for commercial and other
multi-storey buildings, offers the following main advantages
to the designer and client
• The concrete acts together with the steel to create a stiffer,
lighter, less expensive structure .
• Speed and simplicity of construction - Faster to erect,
nearly 25% faster then traditional construction.
• Lighter construction than a traditional concrete building.
• Less material handling at site.
• Has better ductility and hence superior lateral load
behavior; better earthquake resistance.
• Ability to cover large column free area in buildings and
longer span for bridges/flyovers.
• Shear Connections
• Bracing Systems
Anatomy of composite construction
Floors = Slab + Beams
Note: Mainly will discus on
type of floors and connections.
Common Types of Floor Systems
• Concrete slabs supported by open-web joists
• One-way and two-way reinforced concrete slabs
supported on steel beams
• Concrete slab and steel beam composite floors
• Composite profiled decking floors
• Precast concrete floors on steel beams
Note: The most common arrangement found in composite floor
systems is a rolled or built-up steel beam connected to a formed steel
deck and concrete slab. Mostly Profiled Decking Floors system is used
in composite construction.
•Decking with deformed ribs (or embossed decking), as
shown, is commonly used
•The deformations on the ribs allow for a stronger bond
between the concrete and the decking
•Concrete Slab thickness must be ≥ 2” above steel deck
COMPOSITE DECK SLAB
• Composite floor system consists of
steel beams, metal decking and
• They are combined in a very efficient
way so that the best properties of
each material can be used to optimize
• Size of sheeting = 1.8mx0.830m
• Thickness = 1.1mm
(a min. of 0.7 mm ie recommended)
• Yield strength of sheet = 250
• Do not need form work.
• Lightweight concrete is used resulting in
reduced dead weight.
• Decking distributes shrinkage strains, thus
prevents serious cracking.
• Decking stabilizes the beam against lateral
buckling, until the concrete hardens.
Advantages of Profiled decking floors
• Mechanical connectors are used to develop the
composite action between steel beams and concrete.
• This connection is provided mainly to resist
longitudinal shear, and is referred to as the “ shear
REQUIREMENTS OF SHEAR STUDS
• Shear stud diameter ≤ ¾” or ≤ 2.5 tf (prevent tear out).
(tf – thickness of flange or steel deck )
• Shear studs must extend 1½” above top of deck
• They must transfer direct shear at their base.
• They must create a tensile link into the concrete.
• They must be economic to manufacture and fix.
Longitudinal – 6 x stud diameter
Transverse – 4 x stud diameter
Ribs perpendicular:- 4 x stud diameter (long. And trans.)
Maximum spacing 4 x slab thickness or 600mm.
• Spacing of studs :
Conventional and innovative composite beams
Millennium Tower (Vienna - Austria)
EXAMPLES OF COMPOSITE CONSTRUCTION
Total height 202 m
Total ground floor 38000 m2
Time of erection: 8 months
Composite Slim floor beams
Total time of erection: 8 month
max. speed 2 to 2.5 storeys per week!
Parking deck “DEZ” (Innsbruck - Austria)
Ground dimensions 60 x 30 m
Max. span length 10.58 m with
26 cm slim floor slab (= l/40)
Erection of composite columns over 2 storeys
Assembly of prefabricated concrete slabs
Cross section of the slim-floor beam and slab
-200 mm concrete slab
-60 mm prefabricated concrete elements
-steel beam: web 165/20 mm
flange 245/40 mm
-headed studs: 22 mm
COMPARISON OF RCC, STEEL, COMPOSITE
CONSTRUCTION (G+30 STORY)
In the comparative study includes,
• Deflections of the members,
• Size and material consumption of members in composite
with respect to R.C.C. and Steel sections.
• Here Zone IV is taken as per IS 1893 : 2000, a typical office
building plan is selected with area covering 24 m x 42 m.
• Modeling was done with ETABS
As the results show the Steel option is better than R.C.C. But the
Composite option for high rise building is best suited among all three
The reduction in the dead weight of the Steel framed structure is 32
% with respect to R.C.C. frame Structure and Composite framed
structure is 30 % with respect to R.C.C. framed structure.
Axial forces in column have been reduced by average 46% in steel
structure and reduced by average 7% in Composite framed
structure as compared to R.C.C. framed structure.
Steel and composite structure gives more ductility to the structure
as compared to the R.C.C. which is best suited under the effect of
Total saving in the composite option as compared to the R.C.C.
results in 10 % so as with Steel it will be 6-7%.