INTRODUCTION

The main structural and other benefits of using composite floors with
profiled steel decking are:

Savings in steel weight are typically 30% to 50% over non-composite

construction
Greater stiffness of composite beams results in shallower depths for the
same span. Hence lower storey heights are adequate resulting in savings
in cladding costs, reduction in wind loading and savings in foundation
costs.
Faster rate of construction.

the utilisation of the compressive strength of concrete slabs in conjunction

with steel beams, composite floors using profiled sheet decking
completed quickly
steel sheeting acting as the tension reinforcement.

The steel decking performs a number of roles, such as:

It supports loads during construction and acts as a working platform
It develops adequate composite action with concrete to resist the
imposed loading
It transfers in-plane loading by diaphragm action to vertical bracing or
shear walls
It stabilises the compression flanges of the beams against lateral
buckling, until concrete hardens.
It reduces the volume of concrete in tension zone
It distributes shrinkage strains, thus preventing serious cracking of
concrete.

 
 
 
 

 
 
 
 2.0 THE STRUCTURAL ELEMENTS

Profiled decking
Shear connectors
Reinforcement for shrinkage and temperature stresses

the slab thickness

above the profile. Thickness values between 65 and 120 mm

the slab thickness

above the profile. Thickness values between 65 and 120 mm 

2.1 Profiled sheet decking

profile from 0.9 mm to 1.5 mm

galvanised coil.

profile heights are usually in the range of 38-

75 mm

pitch of corrugations is between 150 mm and 350 mm.

spans
of the order of 2.5 m to 3.5 m

the beams are designed

to span between 6 m to 12 m.

2. 2.2 Shear connectors

1.1 Profiled sheeting as permanent form work

Shear connectors are 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 i

nterface.

2.3 Reinforcement for shrinkage and temperature stresses

 
 
 
The effect of shrinkage is
considered and the total shrinkage strain for design may be taken as 0.003 in the absence
of test data.

3.0 BENDING RESISTANCE OF COMPOSITE SLAB

The neutral axis normally lies in the concrete in case of full shear connection;

Fig. 5 Resistance of composite slab to sagging bending

Full shear connection is assumed. Hence, compressive force Ncf in concrete is equal to
steel yield force Npa

where Ap = Effective area per meter width

fyp = Yield strength of steel
gap = Partial safety factor (1.15)

 
 
 
This is valid when x hc, i.e. when the neutral axis lies above steel decking.
Mp.Rd = Ncf (dp - 0.42 x) (3)

Mp.Rd is the design resistance to sagging bending moment.

3.2 Neutral axis within sheeting and full shear connection [Fig. 5(c)]

Normally 3 to 4 m spans can be handled without propping and spans in excess of 4 m will
require propping.

The profiled deck depth normally available ranges from 40 to 85 mm and the metal
thickness 0.6 mm to 2.5 mm. The normal span/depth values for continuous composite slab
should be chosen to be less than 35. The overall depth of the composite slab should not
be less than 90 mm and thickness of concrete, hc, shall not be less than 50 mm.

2.0 DESIGN SITUATIONS

The most important aspect of designer is to ensure an adequate degree of safety and
serviceability of structure.

2.1 Profiled steel sheeting as shuttering

If the central deflection (d) of the profiled deck in non-composite stage is less than l/325
or 20 mm

2.1.1 Loads on profiled sheeting

Design should make appropriate allowances for construction loads, which include the
weight of operatives, concreting plant and any impact or vibration that may occur during
construction.

2.2 Composite slab

4.0 DESIGN TABLES

The manufacturers of the steel profiled sheets normally provide design tables for different
decks made by them

5.0 SERVICEABILITY LIMIT STATES FOR COMPOSITE SLABS WITH

PROFILED DECKS

 
 
 
5.1 Cracking of concrete

Cracking will occur in

the top surface where the slab is continuous over a supporting beam in the hogging
moment regions

longitudinal reinforcement should be provided above internal

supports. The minimum recommended amounts are as 0.2%

5.2 Deflection

deflection of profiled sheeting due to its own weight and the wet concrete slab should not
exceed le /180 or 20 mm, where le is the effective span.

The maximum deflection below the level of the supports should not
exceed span/250, and the increase of deflection after construction (due to creep and to
variable load) should not exceed span/300,

8.0 STEPS IN THE DESIGN OF PROFILED DECKING

The following are the steps for design of profiled decking sheets:
(i) List the decking sheet data (Preferably from manufacturer’s data)
(ii) List the loading
(iii) Design the profiled sheeting as shuttering
Calculate the effective length of the span
Compute factored moments and vertical shear
Check adequacy for moment
Check adequacy for vertical shear
Check deflections
(iv) Design the composite slab – Generally the cross sectional area of the profiled
decking that is needed for the construction stage provides more than sufficient
reinforcement for the composite slab. So, the design of short span continuous
slabs can be done as series of simply supported slabs and top longitudinal
reinforcement is provided for cracking as given in section 5.1. However, longspan
slabs are designed as continuous over supports.
Calculate the effective length of the span
Compute factored moments and vertical shear
Check adequacy for moment
Check adequacy for vertical shear
Check adequacy for longitudinal shear
Check for serviceability, i.e. cracking above supports and deflections

4.0 ULTIMATE LOAD BEHAVIOUR OF COMPOSITE BEAM 

The assumptions made for the analyses of the Ultimate Moment Capacity 

 
 
 
 The tensile strength of concrete is ignored.
• Plane sections of both structural steel and reinforced concrete remain plane after bending.
• The effective area of concrete resists a constant stress of 0.85 (f ) /γ (where (f ) )=cylinder strength
ck cy c ck cy
of concrete; and γ =partial safety factor for concrete) over the depth between plastic neutral axis and
c
the most compressed fibre of concrete.
• The effective area of steel member is stressed to its design yield strength f /γ where f is the yield
y a y
strength of steel and γ is the material safety factor for steel.
a


The notations used here are as follows: ‐ 

 
 

 
 
 
 
4.1 Full shear connection 

3.0 SHEAR CONNECTORS 

3.0 SHEAR CONNECTORS 

These connectors are designed to (a) transmit longitudinal shear along the interface, and (b) Prevent 
separation of steel beam and concrete slab at the interface. 

3.1 Types of shear connectors 

3.1.1 Rigid type 

They derive their resistance from bearing pressure on the concrete, and fail due to crushing of 
concrete. Short bars, angles, T‐sections are common examples of this type of connectors. 

3.1.2 Flexible type 

Headed studs, channels come under this category. These connectors are welded to the flange of the 
steel beam. They derive their stress resistance through bending and undergo large deformation before 
failure 

 
 
 
The shank and the weld collar adjacent to steel beam resist the shear loads whereas the head resists 
the uplift. 

3.1.3 Bond or anchorage type 

These connectors derive their resistance through bond and anchorage action. 

 
 
 
 
 
 
+ve

-ve
Msd=10.57*3.47^2/8 = 15.9 Kn.m/m
 ts fy
D.L

span D.L
Wq L.L = 6*6.5 =39 Kn/m