Stress-Strain Curves for High Strength Concrete at Elevated Temperatures Fu-Ping Cheng 1 ; V. K. R. Kodur 2 ; and Tien-Chih Wang 3 Abstract: The effects of high temperature on the strength and stress-strain relationship of high strength concrete ~HSC! were investi- gated. Stress-strain curve tests were conducted at various temperatures ~20, 100, 200, 400, 600, and 800°C) for four types of HSC. The variables considered in the experimental study included concrete strength, type of aggregate, and the addition of steel fibers. Results from stress-strain curve tests show that plain HSC exhibits brittle properties below 600°C, and ductility above 600°C. HSC with steel fibers exhibits ductility for temperatures over 400°C. The compressive strength of HSC decreases by about a quarter of its room temperature strength within the range of 100– 400°C. The strength further decreases with the increase of temperature and reaches about a quarter of its initial strength at 800°C. The strain at peak loading increases with temperature, from 0.003 at room temperature to 0.02 at 800°C. Further, the increase in strains for carbonate aggregate HSC is larger than that for siliceous aggregate HSC. DOI: 10.1061/~ASCE!0899-1561~2004!16:1~84! CE Database subject headings: Stress strain curves; Fire resistance; High strength concretes; Temperature. Introduction In recent years, high strength concrete ~HSC! is becoming an attractive alternative to traditional normal strength concrete ~NSC!. Concretes of strength in excess of 70 MPa are often used in a wide range of applications. With the increased use of HSC, concern has developed regarding the behavior of such concrete in fire. The high strength in HSC is often obtained, by reducing the amount of water, through the use of special admixtures that also improve the workability. However, the lower water-cement ratio leads to lower porosity that makes HSC more brittle and makes it have less fire endurance at elevated temperatures as compared to NSC. Hence, one of the main concerns for the usage of HSC in fire resistance applications is its performance in fire conditions. Preliminary studies ~Fukujiro et al. 1993; Hsu and Hsu 1994; Khoury 1992; Lankard et al. 1971! have shown that there are well-defined differences between the properties of HSC and NSC at elevated temperatures. In order to understand and eventually predict the performance of HSC structural members, the material properties that determine the behavior of the member at elevated temperatures must be known. The behavior of a structural member exposed to fire is dependent, in part, on the thermal and mechanical properties of the material of which the member is composed ~Castillo and Dur- rani 1990; Fukujiro et al. 1993!. In the past, the fire resistance of structural members could be determined only by testing. In recent years, however, the use of numerical methods for the calculation of the fire resistance of various structural members is gaining wide acceptance. These cal- culation methods are far less costly and time consuming. How- ever, for the use of these calculation methods, the material prop- erties at elevated temperatures are required. One of the basic mechanical properties that is required for the prediction of struc- tural performance under fire conditions is the stress-strain rela- tionship. For developing stress-strain curves of HSC at elevated tem- perature, a joint research project between National Chiao Tung University ~NCTU!, Taiwan, and the National Research Council Canada ~NRCC! is currently in progress. As part of this project, detailed experimental studies were undertaken on four different types of HSC. Both plain HSC and steel fiber reinforced concrete HSC were considered in the study. This is because the addition of steel fibers enhances the mechanical behavior of HSC at elevated tempera- ture and significantly improves the ductility of concrete ~Dieder- ichs et al. 1989; Hsu and Hsu 1994; Lie and Kodur 1996!. Also, two types of commonly used aggregates, siliceous and carbonate, were considered in the tests since the type of aggregate influences the fire performance and the shape of the stress-strain curves. Detailed results from the experimental study are presented in this paper. Research Significance Fire represents one of the more severe exposure conditions and hence provisions of appropriate fire resistance for structural mem- bers are major safety requirements in building design. The fire resistance of structural members is dependent on the thermal and mechanical properties, at elevated temperatures, of the materials of which the members are composed. 1 Associate Professor, Dept. of Civil Engineering, National Chiao Tung Univ., HsinChu, Taiwan. 2 Senior Research Officer, Institute for Research in Construction, National Research Council, Ottawa ON, Canada K1A 0R6. 3 PhD Student, Dept. of Civil Engineering, National Chiao Tung Univ., HsinChu, Taiwan. Note. Associate Editor: Zhishen Wu. Discussion open until July 1, 2004. Separate discussions must be submitted for individual papers. To extend the closing date by one month, a written request must be filed with the ASCE Managing Editor. The manuscript for this paper was submitted for review and possible publication on August 28, 2001; approved on June 11, 2003. This paper is part of the Journal of Materials in Civil Engineering, Vol. 16, No. 1, February 1, 2004. ©ASCE, ISSN 0899- 1561/2004/1-84 –90/$18.00. 84 / JOURNAL OF MATERIALS IN CIVIL ENGINEERING © ASCE / JANUARY/FEBRUARY 2004 J. Mater. Civ. Eng. 2004.16:84-90. Downloaded from ascelibrary.org by National Chiao Tung University on 04/30/14. Copyright ASCE. For personal use only; all rights reserved.
Stress-Strain Curves for High Strength Concrete at Elevated Temperatures
Apr 26, 2023
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