1. COMPOSITE BEAMS-II ©Teaching Resource in Design of Steel Structures –
IIT Madras, SERC Madras, Anna Univ., INSDAG

2. CONTENTS INTRODUCTION PROVISION FOR SERVICE OPENING IN COMPOSITE BEAMS
BASIC DESIGN CONSIDERATIONS
DESIGN OF COMPOSITE BEAMS
EFFECT OF CONTINUITY
SERVICEABILITY
CONCLUSION
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3. (b) Re-entrant profile
INTRODUCTION
Composite beam with profiled sheeting with concrete topping.
Profiled sheets are of two types
Trapezoidal profile
Re-entrant profile
(a) Trapezoidal profile deck
(b) Re-entrant profile
Types of profile deck
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4. ©Teaching Resource in Design of Steel Structures –
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5. The deck slab with profiled sheeting is of two types
The ribs of profiled decks running parallel to the beam.
The ribs of profiled decks running perpendicular to the beam.
Orientation of Profiled deck slab in a composite beam
(b) Ribs perpendicular to
the beam
(a) Ribs parallel to the beam
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6. PROVISION FOR SERVICE OPENING IN COMPOSITE BEAMS
Simple Construction with Rolled Sections
Fabricated Sections
Haunched Beams
Parallel Beam Approach
Castellated Sections
Stub Girders
Composite Trusses
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7. Fabricated Sections (a) Straight Taper (b) Semi-Taper (c)Cranked Taper
(d) Stepped Beam
(where automatic welding is not crucial)
Fabricated sections for commercial buildings
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8. ©Teaching Resource in Design of Steel Structures –
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9. Haunched Beams (a) sections of different size
(b) haunches cut from main beam
Haunched beams: Two types of haunches
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10. ©Teaching Resource in Design of Steel Structures –
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11. Parallel Beam Approach
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12. ©Teaching Resource in Design of Steel Structures –
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13. Castellated Sections
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14. ©Teaching Resource in Design of Steel Structures –
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15. ©Teaching Resource in Design of Steel Structures –
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16. ©Teaching Resource in Design of Steel Structures –
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17. Stub Girders ©Teaching Resource in Design of Steel Structures –
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18. ©Teaching Resource in Design of Steel Structures –
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19. Composite Trusses ©Teaching Resource in Design of Steel Structures –
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20. BASIC DESIGN CONSIDERATIONS
Design Method suggested by Eurocode 4
ultimate strength is determined from plastic capacity.
serviceability is checked using elastic analysis.
full shear connection ensures that full moment capacity of the section develops.
in partial shear connection, the design should be adequate to resist the applied loading.
partial shear connection is sometimes preferred due to economy.
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21. Span to depth ratio Span to Depth ratio as according to EC4 EC4
Simply supported
15-18 (Primary Beams)
18-20 (Secondary Beams)
Continuous
18-22 (Primary Beams)
22-25 (end bays)
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22. Effective breadth of flange
Use of effective width to allow for shear lag
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23. Value of 0 for continuous beam as per EC4
For simply supported beam, effective breadth of simply supported beam is taken as o/8 on each side of the steel web
For continuous beam,
Value of 0 for continuous beam as per EC4
1
2
3
4
0.25(1+2)
0.25(2+3)
0.81
0.72
0.83-0.34
0.73
4+0.53
1.54
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24. Shear flow at interface
Modular ratio
Shear Connection
The elastic shear flow at the interface increases linearly from zero at the centre to its maximum value at the end under uniform load.
At the elastic limit of connectors, redistribution of forces occurs.
At collapse load level it is assumed that all the connectors carry equal force.
The design capacity of shear connectors is taken as 80% of their nominal static strength in EC4.
Shear flow at interface
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25. Load Partial safety factor, f Dead load 1.35 Live load 1.5
Materials Partial safety factor, m
Concrete
Structural Steel
Reinforcement
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26. Section Classifications
Type of Element
Type of Section
Class of Section
Plastic (1)
Compact
(2)
Semi-compact (3)
Outstand element of compression flange
Welded
b/t  7.9
b/t  8.9
b/t  13.6
Rolled
b/t  9.5
b/t  15.0
Internal element of compression flange
b/t  24.2
b/t  26.3
b/t  29.4
b/t  27.3
b/t  33.6
b/t  41.0
Web with neutral axis at mid depth
All
d/t  83.0
d/t  102.9
d/t  126.0
Web under uniform compression
d/t  29.4
d/t  41.0
Single/double angle T-stems
d/t  8.9
b/t  10.0
d/t  10.0
b/t  15.8
d/t  15.8
Circular tube with outer diameter D
D/t  442
D/t  632
D/t  882
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27. DESIGN OF COMPOSITE BEAMS
Moment Resistance
Reinforced Concrete Slabs, supported on Steel beams
beff ds D T t xu
Notations as per IS:
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28. Moment capacity of composite Section with full shear interaction (according to IS:11384 - 1985)
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29. Reinforced concrete slabs, with profiled sheeting supported on steel beams
IS: – 1985, gives no reference to profiled deck slab and partial shear connection
Resistance to sagging bending moment in plastic or compact sections for full interaction.
0.85(fck)cy / c
0.85(fck)cy / c D T t B
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30. Resistance to hogging Bending Moment
hc+ hp D
(a)
fy /a
fsk /s Fs
Fa1
Fa2
(b) a
(c)
Resistance to hogging Bending Moment
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31. ©Teaching Resource in Design of Steel Structures –
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32. The shear force resisted by the structural steel section should
Vertical Shear
The shear force resisted by the structural steel section should
satisfy:
VVp
where, Vp is the plastic shear resistance given by,
The shear buckling of steel web can be neglected if following condition is satisfied
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33. Behaviour of a shear connection fixed through profile sheeting
Effect of shape of deck slab on shear connection
Behaviour of a shear connection fixed
through profile sheeting
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34. Longitudinal Shear Force
Full Shear Connection
Single span beams
V = Fcf =Aa fy/a or
V = 0.85 (fck)cy beff hc/c whichever is smaller.
Continuous span beams
V = Fcf + As fsk /s
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35. Full Shear Connection -I
The number of required shear connectors in the zone under consideration for full composite action is given by:
nf = V /P
The shear connectors are usually equally spaced
Minimum degree of shear connection
Ideal plastic behaviour of the shear connectors may be assumed if a minimum degree of shear connection is provided.
The minimum degree of shear connection is defined by the following equations:
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36. Resistance to combined bending and vertical shear
Interaction between shear and moment V M Mp Vp A o B
0.5Vp Mf
Resistance to combined bending and vertical shear
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37. Surfaces of potential shear failure
Transverse reinforcement
Surfaces of potential shear failure
Truss model analysis
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38. Moment and Shear Coefficients for continuous beam
EFFECT OF CONTINUITY
Moment and Shear Coefficients for continuous beam
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39. EFFECT OF CONTINUITY-I
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40. Inverted – U frame Action
Lateral Torsional Buckling of Continuous Beams
Inverted – U frame Action
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41. SERVICEABILITY Deflection Influence of partial shear connection
Shrinkage induced deflections
Crack Control
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42. CONCLUSIONS
Provision for service opening in composite beams was discussed.
Basic design considerations of composite beams, connected to solid slab, as well as profiled deck slab was discussed.
Effect of continuity on composite beam was discussed.
Serviceability Limit state for composite beam was discussed.
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