COMPOSITE STRUCTURES PREPARED BY : SHAMILAH

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1 COMPOSITE STRUCTURES PREPARED BY : SHAMILAH ANUDAI@ANUAR

2 INTRODUCTION

3 Steel and Concrete Composite Construction Composite construction aims to make each material perform the function it is best at or to strengthen a given cross section of a weaker material Composite structures composed of steel beams and steel column combined with a concrete floor slab Metal decking continuous or single spans

4 Example of Composite Beam

5 Application of composite construction

6 Composite Lock Gate installed in Tilberg

7 Constructing of composite structure

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9 Behaviour of Composite Beams Non-composite beam Composite beam The non-composite is less stiff As the stiffness increase, the increment of moment capacity will lead to reduce the section size.

10 Behaviour of non-composite For non-composite, the concrete slab is not connected to the steel section and behave independently. It is normally weak in longitudinal bending, it deforms to the curvature of the steel section and has its own Neutral Axis (NA). The bottom surface of the concrete slab is free to slide over the top flange of the steel section and can cause slip mechanism..

11 Behaviour of Composite Beams For composite, the concrete slab is connected to the steel section and both act together in carrying the load. Slip between the slab and steel section is now prevented and the connection resists a longitudinal shear force similar in distribution to the vertical shear force..

12 The principal stages in the design of composite beam Materials strengths to be used in the plastic analysis are : Concrete : 0.85 fck/ c ( c = 1.5) 0.57 fck or 0.45 fcu fck 0.8fcu Steel : fy/ a ( a = 1.05) 0.95fy Compressive resistance of the concrete slab is therefore : R c = 0.85f ck γ c b eff h c R c = 0.57 f ck b eff h c Where ; H c is the depth of the concrete slab above the profiled decking Tensile resistance of the steel section is :- R s = A a f y γ a R s = 0.95 f y A a Where ; A s is the area of the steel beam

13 The principal stages in the design of composite beam (cont ) Moment resistance : Mpl, Rd a) Plastic Neutral axis (PNA) in concrete slab : R c R s M pl,rd = R s h 2 + h c + h p R s h c R c 2 y p = R s h c R c from R c h c y p = R s

14 The principal stages in the design of composite beam(cont )

15 The principal stages in the design of composite beam (cont )

16 Shear Resistance

17 Degree of Shear Connection

18 Moment Resistance of composite section with partial shear connection

19 Moment Resistance of composite section with partial shear connection (cont )

20 Local buckling

21 Local buckling (cont )

22 The principal stages in the design of composite beam Preliminary sizing - depth of universal steel beam = span/20 (for simply supported span) = span/24 (for continuous beam) During construction ( for unpropped construction only) - Weight wet concrete + imposed load should be at least 0.75kN/m 2 - at the ULS need to check for bending and shear - at the serviceability limit state (SLS) need to check for deflection Bending and shear of the composite section at the ULS Design of the shear connectors and the transverse steel at the ULS Bending and deflection at the SLS for the composite beam

23 Design of Shear Connectors Shear connectors required to prevent slippage between the concrete flange steel beam, so that concrete and steel can act as a composite unit. The head of shear stud connector can prevent vertical lifting or prising of the concrete away from the steel beam

24 Deflection checks at the serviceability limit state Need to check when:- i) During construction when the concrete flange has not hardened and the steel beam section alone has to carry all the loads due to permanent and variable actions at that time. ii) At service when the concrete has hardened and the composite steel and concrete section carries the additional permanent and variable loads.

25 Deflection during construction The deflection, δ at mid-span for a uniformly distributed load is : 3 xx Where w = udl per metre L = span of beam E a = elastic modulus of steel taken as 210kN/mm 2 (obtained from EC4) I xx = Second moment area of the steel section The deflection due to the permanent action or dead load is locked into beam as the concrete hardens.

26 Deflection at service during the working life of the structure Where E c, eff can be taken as E cm /2 and value of E cm can be obtained from table 1.1 EC4. According to EC4 deflections at service for partial shear connection can be ignored provided that the degree of shear connection, ɳ 0.5

27 Worked Example An unpropped 4.5m span of composite beam as shown in Figure below, need to be designed using 200 x 65 x 1.6 with steel grade S275. Design data Imposed load = 2.5 kn/m 2 Floor Dimension : Span, L = 4.5 m Beam Spacing, b = 1.5m Slab Depth, h t = 130 mm Depth above profile, h c = 80 mm Deck Profiled height, h p = 50 mm *Unpropped construction throughout Shear connectors ; Top-hat shear connectors attached with 4 studs to the beam. Materials: Steel : Grade S275 Nominal value of yield strength, f y = 275N/mm 2 Partial safety factor, γ = 1.0 Design Strength, f d = f y γ = 275N/mm2 Concrete : Normal weight concrete strength class C30/37 Density = 2400 kg/m 3 (23.55 kn/m 3 )

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29 Exercise A 4.5m span beam, propped during construction. Try a 200 x 65 x 1.6 with steel grade S280. h c Design data Imposed load = 2.5 kn/m 2 Floor Dimension : Span, L = 4.5 m Beam Spacing, b = 1.5m Slab Depth, h t = 130 mm Depth above profile, h c = 80 mm Deck Profiled height, h p = 50 mm *Beam propped during construction. Props are placed in the middle of the span Shear connectors ; Top-hat shear connectors attached with 4 studs to the beam. Materials: Steel : Grade S275 Nominal value of yield strength, fy = 275N/mm 2 Partial safety factor, γ = 1.0 Design Strength, f d = f y γ = 275N/mm2 Concrete : Normal weight concrete strength class C30/37 Density = 2400 kg/m 3 (23.55 kn/m 3 )

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32 THANK YOU