FIRE DESIGN OF STEEL MEMBERS - Civil and Natural Resources ...

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7 ADDITIONAL MATERIAL IN EUROCODE 3: 7.1 INTRODUCTION: The Eurocode documents contain a more in-depth description and guidelines on the structural design of steel elements for fire safety than the New Zealand Steel Code. Eurocode 3, ENV 1993-1-2 is the equivalent of Section 11 of NZS 3404, in Europe, but contains a lot more information for designers on the behaviour of steel and the prescribed methods for ensuring the elements will behave adequately in a fire situation. This section of this report analyses what methods or descriptions Eurocode 3 contains in terms of fire safety that NZS 3404 does not, and contains recommendations for aspects of these to be added to the New Zealand Steel Code. Refer to Section 3 for an outline of the present New Zealand Steel Code. ENV 1993-1-2 is a large and quite cumbersome document, so a more concise and simplified version of the methods lacking from NZS 3404 would be better for the New Zealand Steel Code. As seen in Section 3 of this report, the New Zealand Steel Code contains few theoretical methods for estimating the response of steel in elevated temperatures, beyond calculating the limiting temperature of steel and the time until this temperature is reached for unprotected steel. The other methods in NZS 3404 rely on data from standard fire experimental tests to validate and confirm the elements structural safety in fire conditions, which is not always convenient or possible to obtain. Presently, the New Zealand Steel Code concentrates on determining the Period of Structural Adequacy (PSA) of a member by calculating the temperature at which the member will fail when exposed to a fire, and subsequently the time when this temperature is reached can be estimated. Eurocode 3 however, uses theoretical methods of calculating the PSA of a member by evaluating the strength of structural steel members at an elevated temperature. This is an evaluation of the strength of the member rather than an evaluation of the temperatures reached as recommended in the New Zealand Steel Code. These 129
strength design actions are modified by factors that account for the variation of strength of steel with temperature, and decrease the nominal strength of an element. There are a number of changes that can be made to improve Section 11 of NZS 3404 and these are outlined in this section of the report. Changes to the New Zealand Steel Code such as definitions and connection guidelines have not been covered in this report so are not commented on. 7.2 ANALYSIS OF THE EUROCODE: 7.2.1 Design Methods for Performance Requirements: Eurocode 3 states the performance requirement that an element is to be ‘designed and constructed in such a way that they maintain their required load bearing function during the relevant fire exposure’. Deformation criteria must be satisfied if the performance of the member relies on small deflection, ie. if the protection applied to the beam will not remain in place if there is too much deformation of the member. The method in EC3, (1995) follows the principles of normal plastic design, but with modified loads for fire design and with reduced values of the modulus of elasticity and the yield stress of steel to allow for the loss of strength at these temperatures. This is to design structures to satisfy the strength criteria at elevated temperatures, while the New Zealand Steel Code predominantly suggests methods to establish the maximum temperatures reached in a member at elevated temperatures, and the time that this temperature occurs. NZS 3404 makes a provision to allow for the design of members with reduced steel properties for fire design, see Section 3.1.1c. However, there are not detailed guidelines to assist designers in the use of this provision in the code, and the calculations made must be confirmed by an analysis method using experimental data. There are no methods recommended to satisfy this. 130
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Fire Design of Steel Members K R Le
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ABSTRACT: The New Zealand Steel Cod
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TABLE OF CONTENTS: ABSTRACT:.......
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5.4 RESULTS FOR FOUR SIDED EXPOSURE
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LIST OF FIGURES: FIGURE 1.1: VARIAT
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FIGURE 5.11: TEMPERATURE CONTOUR LI
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designed with confidence. Full scal
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eams and struts when subjected to a
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Gilvery and Dexter, (1997), prepare
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with conditions specified to ensure
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1.6 BACKGROUND INFORMATION: 1.6.1 F
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experienced in fire situations, but
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The thermal conductivity is not imp
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[ The heated perimeter of the steel
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The advantages of board systems are
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The values for the thermal properti
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insulation has on the rise of the s
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( T − T ) k H p f s ∆t ∆T
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spreadsheet method very closely, wi
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protection, and for user defined fi
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This equation originates from the y
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1400 1200 1000 800 600 400 200 0 0.
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time. The value of the wall lining
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The Eurocode does not define a meth
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f f y y ( T ) (20) = 1.0 0 < T < 21
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temperature is chosen because it is
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The variation of yield stress data
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15 m -1 < H p /A < 275 m -1 in NZS
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= H p A (m -1 ) 7.85 The cons
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Connections: NZS 3404 requires that
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4 CALCULATION OF STEEL TEMPERATURES
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4.1.2 Analysis Between Methods of T
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Figure 4.2 shows the variation of t
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Minimum temperatures Maximum temper
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For all three sizes of beam, the sp
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Temperature ( o C) 1200 1000 800 60
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The ECCS equation has a time period
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4.3.1 Results from simulations with
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From Figure 4.5 a-c, the formula ra
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Temperature ( o C) 1000 800 600 400
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average temperature of the beam, be
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Temperature ( o C) 1400 1200 1000 8
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significantly decreased from a cool
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Since both programmes use the same
Page 94 and 95: Therefore, the ECCS equations provi
Page 96 and 97: 5 CALCULATION OF STEEL TEMPERATURES
Page 98 and 99: calculations made by the spreadshee
Page 100 and 101: susceptible to heating, heat up mor
Page 102 and 103: Figure 5.3 a-c show the results fro
Page 104 and 105: 7850*600*10500 > 2*775*1100*(1869*2
Page 106 and 107: As can be seen from Figure 5.4 a-c,
Page 108 and 109: 310 UB 40.4 beam H p /A = 241 m -1
Page 110 and 111: The SAFIR results fit between the t
Page 112 and 113: constant specific heat being used i
Page 114 and 115: From Figure 5.7 a-c, it appears tha
Page 116 and 117: 800 Temperature ( o C) 600 400 200
Page 118 and 119: To examine the limits of the thickn
Page 122 and 123: Thermal conductivity, k i = 0.19 W/
Page 126 and 127: the slab except to reduce the secti
Page 128 and 129: Figure 5.14 shows the correlation b
Page 130 and 131: 5.8 CONCLUSIONS: The thermal behavi
Page 132 and 133: 6 COMPARISON OF METHODS USING OTHER
Page 134 and 135: Temperature ( o C) 1200 1000 800 60
Page 136 and 137: 6.2.4 Results for protected steel:
Page 138 and 139: Figures 6.2 b shows the comparison
Page 140 and 141: Figure 6.3 a shows that the average
Page 142 and 143: The fire that the test beams were e
Page 146 and 147: For thermal analysis in Eurocode 3,
Page 148 and 149: To determine the performance of a s
Page 150 and 151: The plastic neutral axis is located
Page 152 and 153: It is therefore recommended that th
Page 154 and 155: These methods may be used to provid
Page 156: Eurocode has a large annex with gui
Page 159 and 160: 8.3 CHANGES TO NZS 3404: The follow
Page 161 and 162: H v height of the ventilation (m) I
Page 163 and 164: EC3, 1995. Eurocode 3: Design of St
Page 165 and 166: Temperature Conditions. National Re
Page 168 and 169: APPENDIX A - SPREADSHEET METHOD: Be
Page 170 and 171: APPENDIX B - SAFIR: In Figure B.2 i
Page 172 and 173: *.str file developed by the pre pro
Page 174 and 175: 22 FISO 23 FISO FISO 24 FISO FISO 2
Page 176: APPENDIX C - FIRECALC Below in Figu
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