Abstract
Studies involving the mechanical properties of high-strength steel (HSS) at elevated temperatures have received considerable attention in recent years. However, current research on HSS at high temperatures is lacking. As a result, the design of fire-protective steel structures with high standards is not sufficiently conservative or safe. This study investigates the effect that elevated temperatures have on the mechanical properties of ASTM A572 Gr. 50 and 60 steels. Reduction factors for the yield strength, tensile strength, and elastic modulus were derived and compared with the standard (AISC, EN1993-1-2) and previous studies (NIST). This study also provides extensive data on the reduction factors for the yield strength, tensile strength, and elastic modulus of mild steel (MS), HSS, and very-high-strength steel (VHSS). The reduction factor for the yield strength was analyzed by expanding the strain level up to 20%. Equations for the yield strength, tensile strength, and elastic modulus were proposed. In future studies, various strains should be analyzed according to the grade of the steel, with the derivation of a reduction factor that considers the plastic strain of the steel. Hence, the findings reported in this study generated a database that can be applied to fire safety design or performance-based fire-resistant design.
Highlights
An elevated temperature of a structure exposed to fire can cause temperature-dependent effects on the building materials, such as concrete and steel [1]
The mechanical properties of ASTM A572 steel at high temperatures are useful for deriving the stress–strain relationship
This study presents a detailed experimental study on the mechanical properties of ASTM A572 Grade 50 (Gr. 50) and Grade 60 (Gr. 60) steels at high temperatures
Summary
An elevated temperature of a structure exposed to fire can cause temperature-dependent effects on the building materials, such as concrete and steel [1]. The stress–strain relationships must be acquired to draw out the mechanical properties at elevated temperatures. Both steady-state and transient-state tests are being used to induce the mechanical properties at high temperatures currently. The steady-state test has been widely used to evaluate the stress–strain relationship of steel members because of its simplicity and practicality [1,2,3]. In a transient-state test, a series of works are required to convert a temperature–strain curve into a stress–strain curve. Many of the research results regarding the stress–strain curve and strength reduction factors at elevated temperatures are reliant on the steady-state test. Most of the steady-state tests disregard the creep effects for the following reasons.
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