【正文】 ays: transientand steadystate tests. In transientstate tests, the test specimen issubjected to a constant load and then exposed to uniformly increasing temperature. Temperature and strain are recorded continuously under constant stress. Thermal strain evaluated from aseparate test is subtracted from the total measured strain Outinen 2007 . In the transientstate tests, the heating rate has a greatin?uence on the strain rate, and thus different heating rates produce different strain rates. Heating rate of steel under ?re conditions depends on the nature of the ?re as well as on insulation andsteel section properties. Generally, for a typical beam with 2 h ?rerated protection, the heating rate of steel can vary between 3 and7 176。Bentz and Prasad 2007。 steel loses its strength and stiffnesswith temperature. The temperature dependent properties that areimportant for modeling the ?re response of steel structures include thermal, mechanical, and deformation properties. Theseproperties vary with temperature and are also dependent on anumber of parameters. Much of the current knowledge on thehightemperature properties of steel is based on limited materialproperty tests. Also, the currently available information for hightemperature material properties is only for the heating phase of?res. This is because most if not all material tests were conducted under either transient or steadystate tests with increasingtemperature. There is a lack of data on material properties in thecooling phase, and this is critical for modeling the response ofsteel structures under realistic ?res.Due to variations in test methods, heating conditions, and datacollection techniques, there is a noticeable variation between thedifferent sets of data available in the literature. Further, until recently, there were no standard test methods for evaluating hightemperature mechanical properties and this led to researchersusing their own test methods to measure the hightemperatureproperties of steel. Thus, there are considerable variations between constitutive relationships presented in different codes andstandards for many of the hightemperature properties of steelKodur and Harmathy 2008 .The variations in hightemperature constitutive models presenta challenge to a designer wishing to model the ?re resistance ofsteel structures. Further, the use of different constitutive modelscan result in different ?re resistance predictions, thus plicating the designers’ option of choosing a reliable constitutivemodel. A stateoftheart review is presented in this paper to il1Professor, Civil and Environmental Engineering, Michigan Statelustrate the variations between available models and test data. TheUniv., East Lansing, MI corresponding author . Email: koduregr.2State Univ., East Lansing, MI. Email: dwaikat1available hightemperature constitutive models for steel are presented, and the effect of variations in constitutive relationships onthe ?re resistance predictions is discussed.3. Candidate, Civil and Environmental Engineering, MichiganState Univ., East Lansing, MI. Email: ?kerustNote. This manuscript was submitted on December 19, 2008。 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。 Steel structures.Author keywords: Performancebased design。 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。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 bet