Eurocode 4: Design of composite steel and concrete structures–

1. EN1994-1-2:2003 Eurocode 4: Design of composite steel and concrete structures– Part 1–2: General rules – Structural fire design Annex F [informative]: Calculation of moment resistances of partially encased steel beams connected to concrete slabs www.structuralfiresafety.org

2. Content Annex A Stress-strain relationships for structural steel General Basic requirements Actions Material design values Verification methods Annex B Stress-strain relationships for siliceous concrete Basis of Design Annex C Stress-strain relationships for concrete adapted to natural fires Structural steel Concrete Reinforcing steel Mechanical & thermal properties Material Properties Partially encased beams Composite columns Tabulated data Annex D Fire resistance of unprotected slabs Unprotected / protected composite slabs Annex E Moment resistance of unprotected beams Composite beams Design Procedures Simple Models Annex F Moment resistance of partially encased beams Composite columns Annex G Simple models for partially encased columns General aspects Thermal response Mechanical response Validation Advanced Models Constructional Details Annex H Simple models for concrete filled columns Annex I Planning & evaluation of experimental models Composite beams Composite columns Connections www.structuralfiresafety.org

3. F.1 Reduced Cross-Section for Sagging Moment Resistance www.structuralfiresafety.org

4. The section of concrete slab is reduced as follows: F.1(1) Flat slab system regardless fire classes fc/γM,fi,c beff Compressive stress in concrete - hc,h hc hc,fi ef ew fay/γM,fi,a Tensile stress in steel + bc h fay,x/γM,fi,a x krfry/γM,fi,s b kafay/γM,fi,a Table F.1 www.structuralfiresafety.org

5. trapezoidal profilestransverse to beam re-entrant profiles transverse to beam F.1(2-3) Other slab systems hc,fi hc,fi hc,fi,min hc,fi≥hc,fi,min prefabricated concrete planks Table F.1 trapezoidal profilesparallel to beam applies hc,fi hc,fi,min heff hc,fi≥hc,fi,min hc,fi Joint between precast elements which is unable to transmit compression stress For calculation refer to Annex D www.structuralfiresafety.org

6. F.1(4) Active width of upper flange (b - 2bfi) (b – 2bfi) varies with fire classes. Yield strength of steel is taken equal to fay/γM,fi,a. fay/γM,fi,a bfi bfi ef ew bc b Table F.2 www.structuralfiresafety.org

7. Web is divided into two parts: F.1(5) Web division ew Top part hh bc h Bottom part x hl b hl are given for different fire classes: For h/bc ≤ 1 or h/bc ≥ 2 Parameters a1 & a2 are given in Table F.3 hl is given directly in Table F.3 For 1< h/bc < 2  Next www.structuralfiresafety.org

8. Table F.3 Bottom part of web: hl ef ew hh bc h hl,min ≤hl ≤hl,max x hl = h – 2ef b www.structuralfiresafety.org

9. Table F.3 Bottom part of web: hl hl,min ≤hl ≤hl,max = h – 2ef www.structuralfiresafety.org

10. Top web fay/γM,fi,a F.1(7-8) Section yield strength ef ew Thereduced yield strength depends on distance x: hh Bottom web bc h x hl Bottom flange kafay/γM,fi,a a0 = 0.018 ef + 0.7 www.structuralfiresafety.org

11. Yield strength decreases with temperature. Reduction factor kr depends on fire class & position of rebar: F.1(9) Yield strength of rebars h bc 2h + bc ew us bc h 3 u2 1 2 u1,3 www.structuralfiresafety.org

12. F.1(11) Shear resistance of web May be verified using the distribution of the design yield strength according to (7) If Vfi,d≥ 0.5Vfi,pl,Rd Resistance of reinforced concrete may be considered www.structuralfiresafety.org

13. F.2 Reduced Cross-Section for Hogging Moment Resistance www.structuralfiresafety.org

14. F.2 Yield strength of rebars Stress in concrete 3 b uh hc + ul - ef Bottom bars u = ui - bc h - hfi Top bars u = hc - uh Stress in steel b Reduction factor ks depends on: • Fire classes • Position of rebars Table F.6 www.structuralfiresafety.org

15. Active width of upper flange: (b – 2bfi) varies with fire classes. Yield strength of steel is taken equal to fay/γM,fi,a. F.1(4) applies as follows: F.2(2) Upper flange fay/γM,fi,a ef bc h hfi b www.structuralfiresafety.org

16. 3 b F.2(3) Reduced concrete section Section is reduced as shown. Compressive strength: bc bc,fi bc,fi h not varying with fire classes fc/γM,fi,c hfi b Table F.7 www.structuralfiresafety.org

17. Reduction factor kr depends on fire class & position of rebar: F.2(4-5) Yield strength of rebars F.1(9) applies as follows: h bc 2h + bc 3 b bc us ew h 3 u2 1 2 u1,3 b www.structuralfiresafety.org

18. F.2(6-7) Shear resistance Assumptions: Shear force is transmitted by steel web, which is neglected when calculating the hogging bending moment resistance. If Vfi,d≥ 0.5Vfi,pl,Rd Resistance of reinforced concrete may be considered www.structuralfiresafety.org

19. End www.structuralfiresafety.org