STAINLESS STEEL IN FIRE (SSIF) - Steel-stainless.org

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4.3.3 Design method for composite columnsThis method is based on the method given in EN 1994-1-2, clause 4.3.5.1(1) [10] .For a given temperature distribution within a cross-sections, the load-bearing capacity of a compositecolumn Nfi,Rdcan be determined from an appropriate column buckling curve which relates the loadbearingcapacity with the elastic critical load, , as follows:Nfi,pl, RdNfi, Rd( λ θ ) Nfi,pl,Rd= χ(4.1)where:χ is the reduction factor depending on the relative slenderness λ θ given by112χ = with ϕ = ( 1+α ( λ θ − λ 0 ) + λ θ)2 2ϕ + ϕ −2Nfi,pl,Rdλ θand α=0.76, λ θ =0.2 (buckling curve d)( A ) ⎛a, jfay,θjAs,kfsy,θk= ∑ + ϕ ⎜c,θ ∑ + ∑jγM,fi,a⎜⎝kγM,fi,smWhere the subscripts a, s and c indicate the <strong>stainless</strong> steel hollow section, the steel reinforcing barsand the concrete, respectively.A a,i , A s,i and A c,i are the areas of elements i of the cross sectionf ay,θ , f sy,θ and f cy,θ are the characteristic strengths at elevated temperature of the steel hollowsection, reinforcing bars and concrete respectively.ϕ c,θ is a reduction coefficient taking into account the differential effects of thermal stresses.The relative slenderness of the column in the fire situation is give by=Nfi,pl,Rλ θ(4.3)WhereNfi,crN fi,pl,R = N fi,pl,Rd with γ M,fi,i = 1.02πN fi,cr =( EI )fi,eff2θlAc,mγfM,fi,cl θ is the buckling length of the column in fire situationThe effective flexural stiffness of the section is calculated as follows:c,θm( EI )fi, eff= ϕa,θ∑ ( Ea,θjla,j) + ϕc,θ[ ∑( Ec,θmlc,m) + ∑( Es,θkls,k)]E i,θ is the characteristic modulus of material i at temperature θ.For steelE a,θ = EFor concrete: E c,θ =323f⎞⎟⎠(4.2)c,θEc,sec,θ= (4.4)2 εcu,θI i is the second moment of area of material i about the principal axes (y-y or z-z) of thecomposite cross section.34
ϕ a,θ and ϕ c,θare reduction coefficients due to the differential effects of thermal stresses.ϕ a,θ depends on the fire rating only and ϕ c,θ is defined by six parameters depending on the cross-sectionsize, column buckling length, reinforcing ratio and fire rating. ϕ c,θ ranges from 0 to 1; when it is 0 thefire resistance of the column is provided by the hollow section only, and when it is 1, the column acts asa composite element with significant interaction between steel and concrete.Appendix A gives the reduction coefficients ϕ a,θ and ϕ c,θ and the Final Work Package Report gives acomplete set of expressions for the buckling resistance under eccentric loading.Comparisons between the proposed design method and the numerical model show that in the majorityof cases, the proposed design method is conservative. A comparison between the proposed designmethod and fire test results show that the difference does not exceed 15%. Moreover, the unsafe resultscorrespond to columns which failed after 60 minutes, the maximum fire rating for which the proposeddesign method is valid. For the tests in the range of application of the proposed method, all thepredictions were conservative.4.3.4 Parametric studies for composite beams2D thermal analyses were carried out to establish simplified temperature distributions for exposure tothe standard fire curve for 120 minutes for eight integrated floor beams (IF beam no. 1 in Figure 4.3)and seven slim floor beams (SF beam no. 2 in Figure 4.3). Figure 4.5 shows the results for the IFbeams. In all cases there is a large temperature gradient in the cross section due to the encasement ofconcrete. After 30 minutes, the carbon steel remains below 400°C (full strength). After 60 minutes, upto 25% of the depth of the web is above 400°C. After 120 minutes, about 50% of the carbon steelsection is above 400°C. The unexposed side remains at a temperature lower than 100°C after 120minutes of fire exposure. This means that the insulation criterion is always satisfied with this type ofstructural member.<strong>Steel</strong> temperature (°C)10009008007006001/2 IPE400-380x10 1/2 IPE400-380x10 1/2 IPE400-380x101/2 IPE400-380x10 1/2 HEB300-500x15 1/2 HEB300-500x151/2 HEB300-500x15 1/2 HEB300-500x15 1/2 IPE500-400x121/2 IPE500-400x12 1/2 IPE500-400x12 1/2 IPE500-400x121/2 HE500-500x20 1/2 HE500-500x20 1/2 HE500-500x201/2 HEB600 500x20 1/2 HEB600 500x20 1/2 HEB600 500x201/2 HEB600 500x20 1/2 HEB600 500x20 1/2 HEA450 500x151/2 HEA450 500x15 1/2 HEA450 500x15 1/2 HEA450 500x15500400300200100R60R30R120R900-25 0 25 50 75 100 125 150 175 200 225 250 275 300Depth on the beam (mm)Stainless steelplateCarbon steel profileFigure 4.5 Temperature distribution along the depth of IF beams from 30 to 120minutes of standard fire exposure35
Page 1 and 2: Research Programme of the Research
Page 3 and 4: CONTENTSPage No.ABSTRACT 5FINAL SUM
Page 5: ABSTRACTThe relatively sparse body
Page 9: 8. WP7: Design aids and softwareRat
Page 12 and 13: 1.2Stiffness E( ) retention / E(20
Page 15 and 16: 3 WP1: FIRE RESISTANT STRUCTURES AN
Page 17 and 18: ExposedMid-depth ofinsulationInnerp
Page 20 and 21: system thus achieved a 60 minute fi
Page 22 and 23: than the carbon steel columns; the
Page 24 and 25: For case 1 (pinned ends), the stain
Page 26 and 27: 10 68.5 10 61.5θg2= 20°C; α = 9
Page 28 and 29: of part of the cross-section being
Page 30 and 31: Load testing:1000 kN PressEnd plate
Page 32 and 33: Table 4.3 shows failure times, fire
Page 36 and 37: 4.3.5 Design method for composite b
Page 38 and 39: 4.3.6 Comparison between stainless
Page 41 and 42: 5 WP3: CLASS 4 CROSS SECTIONS IN FI
Page 43 and 44: FWater cooled steelload equipmentSu
Page 45 and 46: Table 5.4 Comparison of strength re
Page 47 and 48: 5.3.3 Development of design guidanc
Page 49 and 50: 6 WP4: PROPERTIES AT ELEVATEDTEMPER
Page 51 and 52: Table 6.3Test programme for transie
Page 53 and 54: The following procedure used to eva
Page 55: Table 6.4Material reduction factors
Page 58 and 59: T= 100 °C T=200°CT= 300 °C T=400
Page 60 and 61: Grade 1.4318: Welded (W) v.s. Base
Page 62 and 63: Figure 7.5Connection design for bol
Page 64 and 65: Table 7.2Detailed results of shear
Page 66 and 67: dilatation caused by heating may ca
Page 69 and 70: 8 WP6: PARAMETRIC FIRE DESIGNDetail
Page 71 and 72: Table 8.1Cross-sectionTemperature f
Page 73 and 74: analyses (Figure 8.2). The differen
Page 75 and 76: calculated according to EN 1993-1-4
Page 77 and 78: The following observations were not
Page 79 and 80: 9 WP7: DESIGN AIDS AND SOFTWARE9.1
Page 81 and 82: 9.3 Design of stainless steel beams
Page 83 and 84: Figure 9.4Column buckling tests at
Page 85 and 86:
The main assumptions made by the so
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Figure 9.7Fire design software: fir
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11 FINAL WORK PACKAGE REPORTSAll de
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12.2 Dissemination of project resul
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13 CONCLUSIONSThis report summarise
Page 100 and 101:
Figure 6.3 EN 1.4541 steel stress-s
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Table 8.5 Buckling resistance at ro
Page 104 and 105:
[22] ECSC Final Report, Development
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Table A.4Values of parameters L θ
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Table B.1Experimental data on stain
Page 110 and 111:
EUROPEAN COMMISSIONRESEARCH DIRECTO
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Page 114 and 115:
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