# Mechanical Properties of ASTM A572 Grades 50 and 60 Steels at High Temperatures
## 1 Introduction
The recent research can be summarized as follows. [PERSON] et al. [13] examined the reduction factors for the yield strength, elastic modulus, and ultimate strength using high-strength structural steel. They also covered the thermal characteristics of MS as compared with HSS. They showed that the thermal characteristics of HSS are different from those of MS. However, there is no presented regression equation for strength reduction depending on high-strength steel and mild steel by temperature. [PERSON] et al. [14] investigated HSS using S690 in a fire scenario. They verified the thermal properties of HSS using both steady- and transient-state tests. The results of the HSS S690 test were compared with the AISC (American), ASCE (American), Eurocode 3 (European), and AS 4100 (Australian) standards. As a result of the comparison, it was found that the current design standard cannot be safely applied to the fire-resistant design of steel structures using HSS S690. The study of [PERSON] derives significant data on mechanical properties at high temperatures, as in the study of [PERSON] et al. [13], but the regression equation for HSS S690 was not presented. In addition, the results and differences for high-strength steel compared to mild steel were not described. [PERSON] et al. [15] also evaluated the residual strength of a fire-exposed steel bridge girder. In their FEM modeling studies, a case study of a steel bridge girder showed a residual capacity of \(\sim\)84% at a fire temperature of 680 \({}^{\circ}\)C. In order to check the thermal and structural response of the steel bridge girder exposed to fire, the thermal and mechani \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Yield Strength** & **Type** & **Description** & **Typical Example** & **Application** \\ \hline \multirow{2}{*}{\(<\)400} & Mild steel & \multirow{2}{*}{Regular structural steel} & SS235 (S8400), SM355 & \multirow{2}{*}{Buildings} \\  & (MS) & & (SM490), A572 (Gr. 50), & \\  & & & S350, S355, A992 & \\ \hline \multirow{2}{*}{400–690} & High-strength steel & High-performance steel/high & \multirow{2}{*}{A572 (Gr. 60), S460} & \multirow{2}{*}{Bridges, high-rise buildings} \\  & (HSS) & tensile steel & & \\ \hline \multirow{2}{*}{\(>\)690} & Very-high-strength steel & \multirow{2}{*}{Ultra/super-high-strength steel} & \multirow{2}{*}{S690, S960} & \multirow{2}{*}{Cranes, bridges, high-rise buildings, offshore structures} \\  & (VHSS) & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Types and applications of steel according to the yield strength. cal properties of the steel were entered into a finite element analysis program (ANSYS). The high-temperature mechanical properties of steel are useful for FEM analysis. [PERSON] et al. [16] obtained the post-fire elastic modulus, yield and ultimate strength reductions, ductility reductions, and stress-strain curves of HSS (S460, S690). Their results showed that the steel grade has a significant influence on the post-fire residual mechanical properties of HSS. They found that the post-fire mechanical properties of S460 and S690 are not affected until they are exposed to temperatures above 600 \({}^{\circ}\)C.  
[PERSON] et al. [17] presented results from experimental studies on the high-temperature properties of high-strength Q460 steel. Based on their results, they concluded that high-strength Q460 steel exhibits a slower loss of strength and stiffness than MS throughout a temperature range of 20-800 \({}^{\circ}\)C. Moreover, [PERSON] proposed the elastic modulus equation for high-strength steel Q460, but there was a difference from Eurocode 3 based on mild steel. This study contained significant results on the elastic modulus of Q460 steel, but the detailed results and related equations for the difference between mild steel and high-strength steel were somewhat insufficient. [PERSON] et al. [18] estimated the stress-strain of ASTM A992 steel at elevated temperatures from 20 to 1000 \({}^{\circ}\)C with strain regions at both 5% and 20%.