Design details of Steel concrete composite flooring using profiled deck sheets and lightweight concrete; their bending and shear strengths and their serviceability criteria are given in this slide

1. 2016233028
SEMINAR-2

2. Concrete
(Good in compression)
Steel
(Good in tension)
Composite
Construction
(High strength &
stiffness)

3.  Effective utilization of materials
 Better seismic resistance
 Withstand numerous loading cycles before
fracture.
 High energy absorbing
 Faster construction
 Better Quality Assurance
 Cost effective
 Steel is more durable & highly recyclable
 Lesser foundation costs.
 Cost of formwork is lower
 Experience lesser deflection

4.  Metal decking then concrete,
either lightweight or normal
weight
 Metal decking acts as long-lasting
framework for the concrete,
eradicating the need for props,
and as a malleable reinforcement
for the slab.
 In case of fire, there are steel bars
embedded in the concrete slabs,
which prevent cracking and
safeguards against degradation of
the decking.

5. In-situ concrete
Profiled decking
Shear connectors
Bar reinforcement

6. Light-weight concrete is
popular, despite its slightly
higher initial cost, because of
the consequent reduction in
weight and enhanced fire-
insulation properties.

7. •0.9 – 1.5 mm
Galvanized
coil thickness
•38 - 75 mmProfile height
•150 - 350 mm
Pitch of
Corrugations

8.  Steel is galvanized before forming
(designated by GD #No. that specifies
grams of zinc per m2 )
 GD 275 is sufficient to achieve excellent
service life in internal applications with
mild exposure
 Above 275, it is difficult to obtain and
also hinders Thru-deck welding
 To increase service life, polyester paints
can be applied over galvanized steel

9. Type of decking is decided based on
 Bond at the steel-concrete interface
 Stability while supporting wet concrete and other
construction loads
Indentations and protrusions into the rib increase
bearing resistance in addition to adhesion and also
provide the shear transfer in composite slabs.
Dovetail profile
Trapezoidal profile with web indentations

11. Commercial product of
TATA Steel – ComFlor 46
Trapezoidal decking installed
on down-stand beams

12. Steel elements such as studs, bars,
spiral or any other similar devices
welded to the top flange of the steel
section and intended to transmit the
horizontal shear between the steel
section and the cast in-situ concrete
and also to prevent vertical separation
at the interface.

14. A typical run of stud shear connectors

15. Supplementary bar reinforcement are placed
 To achieve longer fire resistance
 To reinforce slab around significant
openings
 When additional transverse reinforcement is
needed
 To achieve greater crack control

16. In buildings, temperature difference in
the slabs is negligible; thus there is no
need to provide reinforcement to account
for temperature stresses.
The effect of shrinkage is considered and
the total shrinkage strain for design may
be taken as 0.003

17. According to EN 1994-1-1, the following
methods of analysis may be used for
composite slabs at the ultimate limit state:
a) Linear-elastic analysis with, or without
redistribution.
b) Rigid plastic global analysis provided that it
is shown that sections where plastic
rotations are required have sufficient
rotation capacity.
c) Elastic-plastic analysis, taking into account
the non-linear material properties.

18.  As the sheeting is provided in two-span
lengths, together with the fact that the
concrete is cast on top of the sheets
without joints, the composite slab is
normally continuous.
 However, although the finished slab is
continuous, it can sometimes be beneficial
for designers to assume that it is simply-
supported in normal conditions and use
linear-elastic analysis.

19.  NO INDIAN STANDARD CODES
 EC-4 is found to be most accurate for
COMPOSITE CONSTRUCTION
 Slab be checked for bending capacity, assuming
full bond between concrete and steel, then for
shear bond capacity and, finally, for vertical
shear.
 The analysis of the bending capacity of the slab
may be carried out as though the slab was of
reinforced concrete with the steel deck setting
as reinforcement.

20. In calculating the sagging bending resistance of
the composite slab using simple plastic theory,
there are three possible cases that may be
encountered in practical design
 Neutral axis above the sheeting and full shear
connection (η = 1)
 Neutral axis within the sheeting and full shear
connection (η = 1)
 Partial shear connection (0 <η < 1)

21. Degree of shear connection, η = Nc / Nc,f
where Nc = compression force in concrete
Nc,f = compression force in concrete for full
shear connection.
For η = 0, composite action between the steel sheet
and the concrete does not exist and it is assumed that
the bending resistance is provided by the profiled
steel sheet alone.
For η = 1, full shear connection exists such that the
full tensile resistance of the sheet is developed, or the
full compressive resistance of concrete above the ribs
of the sheet is mobilised.
For intermediate cases such that 0 < η < 1, partial
shear connection exists; this case is typical for open
trough profiled steel sheets.

22. The shear resistance of composite slab largely
depends on connection between profiled deck and
concrete. The following three types of
mechanisms are mobilised:
(i) Natural bond between concrete and steel due
to adhesion
(ii) Mechanical interlock provided by dimples on
sheet and shear connectors
(iii) Provision of end anchorage by shot fired pins
or by welding studs when sheeting is made to rest
on steel beams.

23. Cracking
Crack width ≤3 mm
Min Reinf. for propped construction - 0.4 %
Min Reinf. for un-propped construction - 0.2 %
If environment is corrosive it is advisable to
design the slab as continuous and take advantage
of steel provided for negative bending moment for
resisting cracking during service loads.

24. Deflection
Span to depth ratio - 25 (simply supported
slabs)
- 35 (continuous slabs)
for the composite condition.
Deflection limits - l/180 or
- 20 mm which ever is less
for un-propped construction.

25. Fire endurance
The fire endurance is assumed based on the
following two criteria:
 Thermal insulation criterion concerned with
limiting the transmission of heat by conduction
 Integrity criterion concerned with preventing
the flames and hot gases to nearby
compartments.
It is met by specifying adequate thickness of
insulation to protect combustible materials.
Fire rating - R60 (failure time is more than 60
minutes) for normal buildings

26. Vibration
In most buildings, following two cases are considered
i) People walking across a floor with a pace frequency
between 1.4 Hz and 2.5 Hz.
ii) An impulse such as the effect of the fall of a heavy object.
BS 6472 present models of human response to vibration in the
form of a base curve.
Here root mean square acceleration of the floor is plotted
against its natural frequency f0 for acceptable level R based on
human response for different situations such as, hospitals,
offices etc.
R=1 for “minimal level of adverse comments from occupants” of
sensitive locations such as hospital, operating theatre and
precision laboratories.
R = 4 for offices
R = 8 for workshops

27.  BURJ KHALIFA (DUBAI)
 NOVA VICTORIA (LONDON)
 Luxembourg Chamber of Commerce (EURPOE)
 ICICI BANK (HYDERABAD, INDIA)
 UNION SQUARE (ABERDEEN, SCOTLAND)
 TECHNOVIUM (NETHERLAND)
 THE BOILER HOUSE (ENGLAND)
 TWO SNOWHILL (BIRMINGHAM)
 SAINT MARK'S PRIMARY SCHOOL (HAMILTON,UK)

28. 1) Eurocode-4: Design of composite steel and concrete structures,
Composite slabs, EN 1994 -1-1:2004, BSI.
2) Johnson, R.P, Composite Structures of Steel and Concrete:
Beams, Slabs, Columns and Frames for Buildings (Third Edition),
Blackwell Publishing, 2004.
3) Hicks, S.J., Lawson, R.M., Rackham, J.W. and Fordham. P,
Comparative Structure Cost of Modern Commercial Buildings
(Second Edition), SCI Publication 137, The Steel Construction
Institute, Ascot, p 85, 2004.
4) Rackham J W, Couchman G H and Hicks J K, Composite slabs
and beams using Steel Decking: Best practice for design and
construction, MCRMA, Technical paper- 13, Steel Construction
Institute Publication -300, 2009.