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

CONTENTS INTRODUCTION PROVISION FOR SERVICE OPENING IN COMPOSITE BEAMS BASIC DESIGN CONSIDERATIONS DESIGN OF COMPOSITE BEAMS EFFECT OF CONTINUITY SERVICEABILITY CONCLUSION ©Teaching Resource in Design of Steel Structures – IIT Madras, SERC Madras, Anna Univ., INSDAG

(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 ©Teaching Resource in Design of Steel Structures – IIT Madras, SERC Madras, Anna Univ., INSDAG

©Teaching Resource in Design of Steel Structures – IIT Madras, SERC Madras, Anna Univ., INSDAG

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 ©Teaching Resource in Design of Steel Structures – IIT Madras, SERC Madras, Anna Univ., INSDAG

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 ©Teaching Resource in Design of Steel Structures – IIT Madras, SERC Madras, Anna Univ., INSDAG

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 ©Teaching Resource in Design of Steel Structures – IIT Madras, SERC Madras, Anna Univ., INSDAG

©Teaching Resource in Design of Steel Structures – IIT Madras, SERC Madras, Anna Univ., INSDAG

Haunched Beams (a) sections of different size (b) haunches cut from main beam Haunched beams: Two types of haunches ©Teaching Resource in Design of Steel Structures – IIT Madras, SERC Madras, Anna Univ., INSDAG

©Teaching Resource in Design of Steel Structures – IIT Madras, SERC Madras, Anna Univ., INSDAG

Parallel Beam Approach ©Teaching Resource in Design of Steel Structures – IIT Madras, SERC Madras, Anna Univ., INSDAG

©Teaching Resource in Design of Steel Structures – IIT Madras, SERC Madras, Anna Univ., INSDAG

Castellated Sections ©Teaching Resource in Design of Steel Structures – IIT Madras, SERC Madras, Anna Univ., INSDAG

©Teaching Resource in Design of Steel Structures – IIT Madras, SERC Madras, Anna Univ., INSDAG

©Teaching Resource in Design of Steel Structures – IIT Madras, SERC Madras, Anna Univ., INSDAG

©Teaching Resource in Design of Steel Structures – IIT Madras, SERC Madras, Anna Univ., INSDAG

Stub Girders ©Teaching Resource in Design of Steel Structures – IIT Madras, SERC Madras, Anna Univ., INSDAG

©Teaching Resource in Design of Steel Structures – IIT Madras, SERC Madras, Anna Univ., INSDAG

Composite Trusses ©Teaching Resource in Design of Steel Structures – IIT Madras, SERC Madras, Anna Univ., INSDAG

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. ©Teaching Resource in Design of Steel Structures – IIT Madras, SERC Madras, Anna Univ., INSDAG

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) ©Teaching Resource in Design of Steel Structures – IIT Madras, SERC Madras, Anna Univ., INSDAG

Effective breadth of flange Use of effective width to allow for shear lag ©Teaching Resource in Design of Steel Structures – IIT Madras, SERC Madras, Anna Univ., INSDAG

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 ©Teaching Resource in Design of Steel Structures – IIT Madras, SERC Madras, Anna Univ., INSDAG

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 ©Teaching Resource in Design of Steel Structures – IIT Madras, SERC Madras, Anna Univ., INSDAG

Load Partial safety factor, f Dead load 1.35 Live load 1.5 Materials Partial safety factor, m Concrete 1.5 Structural Steel 1.15 Reinforcement 1.15 ©Teaching Resource in Design of Steel Structures – IIT Madras, SERC Madras, Anna Univ., INSDAG

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 ©Teaching Resource in Design of Steel Structures – IIT Madras, SERC Madras, Anna Univ., INSDAG

DESIGN OF COMPOSITE BEAMS Moment Resistance Reinforced Concrete Slabs, supported on Steel beams beff ds D T t xu Notations as per IS: 11384-1985 ©Teaching Resource in Design of Steel Structures – IIT Madras, SERC Madras, Anna Univ., INSDAG

Moment capacity of composite Section with full shear interaction (according to IS:11384 - 1985) ©Teaching Resource in Design of Steel Structures – IIT Madras, SERC Madras, Anna Univ., INSDAG

Reinforced concrete slabs, with profiled sheeting supported on steel beams IS: 11384 – 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 ©Teaching Resource in Design of Steel Structures – IIT Madras, SERC Madras, Anna Univ., INSDAG

Resistance to hogging Bending Moment hc+ hp D (a) fy /a fsk /s Fs Fa1 Fa2 (b) a (c) Resistance to hogging Bending Moment ©Teaching Resource in Design of Steel Structures – IIT Madras, SERC Madras, Anna Univ., INSDAG

©Teaching Resource in Design of Steel Structures – IIT Madras, SERC Madras, Anna Univ., INSDAG

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 ©Teaching Resource in Design of Steel Structures – IIT Madras, SERC Madras, Anna Univ., INSDAG

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 ©Teaching Resource in Design of Steel Structures – IIT Madras, SERC Madras, Anna Univ., INSDAG

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 ©Teaching Resource in Design of Steel Structures – IIT Madras, SERC Madras, Anna Univ., INSDAG

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: ©Teaching Resource in Design of Steel Structures – IIT Madras, SERC Madras, Anna Univ., INSDAG

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 ©Teaching Resource in Design of Steel Structures – IIT Madras, SERC Madras, Anna Univ., INSDAG

Surfaces of potential shear failure Transverse reinforcement Surfaces of potential shear failure Truss model analysis ©Teaching Resource in Design of Steel Structures – IIT Madras, SERC Madras, Anna Univ., INSDAG

Moment and Shear Coefficients for continuous beam EFFECT OF CONTINUITY Moment and Shear Coefficients for continuous beam ©Teaching Resource in Design of Steel Structures – IIT Madras, SERC Madras, Anna Univ., INSDAG

EFFECT OF CONTINUITY-I ©Teaching Resource in Design of Steel Structures – IIT Madras, SERC Madras, Anna Univ., INSDAG

Inverted – U frame Action Lateral Torsional Buckling of Continuous Beams Inverted – U frame Action ©Teaching Resource in Design of Steel Structures – IIT Madras, SERC Madras, Anna Univ., INSDAG

SERVICEABILITY Deflection Influence of partial shear connection Shrinkage induced deflections Crack Control ©Teaching Resource in Design of Steel Structures – IIT Madras, SERC Madras, Anna Univ., INSDAG

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. ©Teaching Resource in Design of Steel Structures – IIT Madras, SERC Madras, Anna Univ., INSDAG