| Summary: | This study aims to study the structural behavior of axially-restrained high strength concrete (HSC) columns under fire. To achieve this, a material model for HSC under high temperature is developed. The model includes transient strain in an explicit way, and is an extension of Kodur’s work. An existing FEM program is extended by incorporating the proposed material model. Structural behavior of HSC columns under fire is predicted through this program. When an axially-restrained column is heated, great axial force develops. Since transient strain is significantly related to external force, in this case, the method of calculating transient strain has a considerable effect on structural behavior. In other words, implicit or explicit inclusion of transient strain yields different results for the development of internal compression force. Therefore, axial restraint and transient strain are of principal interest in this research. By comparison of different material models, the nature of transient strain is investigated. The author proposed an equation to calculate transient strain. Based on this equation, a HSC material model which explicitly includes transient strain is established. The validity of the material model is verified by some material tests. The interaction between axial restraint and transient strain is analyzed using the FEM program. The FEM program is further verified by some case studies. Through the comparison of numerical and test results, it is demonstrated that when there is no axial restraint, implicit and explicit models give similar results. However, if axial restraint is present, explicit model gives more reasonable results than implicit model.
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