【正文】 State Univ., East Lansing, MI. Email: ?kerustNote. This manuscript was submitted on December 19, 2008。 Fire resistance。 and Rustin Fike3Abstract: Fire is one of the most severe conditions to which structures can be subjected, and hence, the provision of appropriate ?resafety measures for structural members is an important aspect of design. The recent introduction of performancebased codes hasincreased the use of puterbased models for ?re resistance assessment. For evaluating the ?re resistance of steel structures, hightemperature properties of steel are to be speci?ed as input data. This paper reviews hightemperature constitutive relationships for steelcurrently available in American and European standards, and highlights the variation between these relationships through parison withpublished experimental results. The effect of various constitutive models on overall ?re resistance predictions is illustrated through casestudies. It is also shown that hightemperature creep, which is not often included in constitutive models, has a signi?cant in?uence on the?re response of steel structures. Results from the case studies are used to draw remendations on the use of appropriate constitutivemodels for ?re resistance assessment.DOI: CE Database subject headings: Constitutive relations。 Mahmud Dwaikat2。 Steel structures.Author keywords: Performancebased design。 Structural steel.IntroductionStructural ?re safety is one of the primary considerations in thedesign of highrise buildings where steel is often the material ofchoice for structural members. At present, structural ?re safety?re resistance of steel members is generally achieved throughprescriptive approaches which are based on either standard ?reresistance tests or empirical calculation methods. These prescriptive based approaches have major drawbacks and do not providea rational or realistic ?re resistance assessment. The recent movetoward performancebased ?re design has increased the focus onthe use of puter simulations for evaluating ?re resistance ofstructural members. Knowledge of hightemperature properties ofsteel is critical for evaluating ?re resistance using numerical models.Steel has excellent strength properties at ambient temperature,however, like other materials。 separate discussions must besubmitted for individual papers. This paper is part of the Journal ofMaterials in Civil Engineering, Vol. 22, No. 5, May 1, 2010. 169。 ASCE 1992 , as well as published test data,were used to pile Figs. 1 and 2 Rempe and Knudson 2008。Yawata Iron and Steel Co. 1969 . The Eurocode and ASCEmanual specify empirical relationships for thermal conductivityand speci?c heat as functions of temperature, these relationshipsare presented in the “Thermal Properties” section of the Appendix.It can be seen from Fig. 1 that thermal conductivity decreasewith temperature in an almost linear fashion, and there is littlevariation between the models presented in ASCE manual and Eurocode. On the contrary, published speci?c heat models vary considerably above 700176。 C seen in Fig. 2. The variation between the testdata and the models shown in Fig. 2 is partly due to the fact thatthe majority of the existing data on speci?c heat originates fromstudies carried out on iron and nonstructural steel alloys. Additionally, the maximum temperature reached in these studies ofiron and nonstructural steel was below 750176。 C / min.This heating rate can be suitable for unprotected steel members,but not for protected members with slow heating rates.On the other hand, the steadystate tests are generally fasterand easier to conduct than the transientstate tests. In the steadystate tests, the test specimen is heated to a speci?c temperatureFig. 3. Yield strength of steel as predicted by different models and asmeasured in different testsand after that a tensile test is carried out. Stress and strain valuesare recorded continuously under constant temperature. The testcan be either loadcontrolled loading rate is constant or strainFig. 4. Elastic modulus of steel as predicted by different models andas measured in different testsperatures for longer time duration, therefore, other factors, suchas hightemperature creep timedependent plastic strain undercontrolled strain rate is constantOutinen 2007。 C. This variation can be attributed to many factors, primarily variable heating and strain/load rates during thetest. For example, when the heating rate of the stressed specimenis small, the specimen will be subjected to stress at elevated temtemperaturestressstrain curves of the tested specimen.The yield strength and elastic modulus constitutive relationships from the ASCE manual, Eurocode, and those proposed byPoh 2001 are also shown in Figs. 3 and 4, respectively. Thehightemperature reduction factors for the yield strength and elastic modulus of steel