Critical Review of Test Methods for Mechanical Characterization of Steel for Structural-Fire Engineering Applications

Abstract

Knowledge of elevated-temperature mechanical properties of structural steel is essential for accurate evaluation of structural behavior in a fire. As a result, various test procedures have been adopted to obtain the stress–strain behavior and to establish elevated-temperature mechanical properties of structural steel suitable for structural-fire applications. This paper provides a critical review of steady-state and transient-state temperature material tests, the two common methods of characterizing the mechanical behavior of structural steel subjected to fire. The main focus in this review is the thermal creep of steel and how it is modeled in each material test. It is indicated that these two test methods result in rate-dependent stress–strain curves, in which creep effects are implicit in the behavior of steel at elevated temperatures. Alternatively, steady-state temperature creep tests allow for the explicit consideration of thermal creep in the form of isochronous stress–strain curves. It is shown that creep can result in significant time- and temperature-dependent reductions in the strength of structural steel in fire and that the adopted method of characterizing the stress–strain behavior of steel for structural-fire engineering applications can lead to underestimation of creep effects depending on the applied stress, temperature, and steel grade.