Determination of Physico-Mechanical Properties and High Temperature Behavior of Stressed Reinforcing Steels

Abstract

This study experimentally investigated the effect of fire-induced high temperature on different grades of stressed steels. The steel in the reinforced concrete structural element is under the influence of static and dynamic loads. The main approach of this study is based on stresses caused by static and dynamic loads on steel reinforcing bars (rebars) and the effect of high temperature during this process. Three different grades of steel (smooth S220, ribbed S420, Tempcore ribbed B500C) in three different diameters (∅12, ∅16, ∅20) were used. The three loading conditions taken into account for reinforced steels subjected to high temperatures were the design yield strength (fyd: fyk/1.15), the characteristic yield strength of steel rebar (fyk) and the exceeding yield strength (fye: fyk × 1.15). Three different temperatures (75, 150 and 300°C) were applied depending on concrete cover thickness and fire duration. Physical and mechanical properties of the test specimens were determined prior to high temperature. Metallographic investigations, hardness measurement, impact toughness, oxidation layer measurement, electrochemical oxidation test and tensile test were performed on steel rebars. Results showed that pre-tension and high temperatures caused drastic changes in steel characteristics. Results provided information about how steels commonly used in the construction of reinforced concrete structures are affected by fire and about at what stage of the fire they start to be affected.