## 4 Calibration Tensile Test at Elevated Temperature  
### Uniaxial Tensile Tests on S690 Structural Steel  
The dimension of a S690 structural steel specimen for a standard uniaxial tensile test at an elevated temperature is the same as shown in Figure 4. The standard uniaxial tensile tests at an elevated temperature were also conducted on a servo-hydraulic testing machine, with a maximum stroke displacement of 75 mm and a capacity of 500 kN as shown in Figure 12. A specimen of S690 high-strength steel was installed and heated by a tubular high-temperature furnace as shown in Figure 13. The heat part was a split-tube furnace with a three-zone configuration and a side view window. A type K thermocouple was mounted at the centre of each zone to measure the heating temperature. The specimen was heated to 400 \({}^{\circ}\)C at the heat rate of 10 \({}^{\circ}\)C/min and subject to tension [18]. Both the extensometer and CCDC system were used to measure the strain in the specimen under the applied tension force. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Mechanical Properties** & **Specimen 1** & **Specimen 2** & **Specimen 3** & **Specimen 4** & **Average Value** \\ \hline Elastic Modulus (E/GPa) & 195.1 & 191.2 & 193.7 & 192.9 & 193.2 \\ Yield Strength (\(f_{y}\) /MPa) & 1729 & 1725 & 1710 & 1709 & 1718. \\ Ultimate Strength (\(f_{u}\)/MPa) & 2017.2 & 2008.2 & 2014.3 & 2015.9 & 2015.9 \\ Fracture Strain (\(\epsilon_{u}\)) & 0.0558 & 0.0548 & 0.0462 & 0.0527 & 0.0524 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Mechanical properties of pre-tension steel cables obtained by CCDC system. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Mechanical Properties** & **Specimen 1** & **Specimen 2** & **Specimen 3** & **Specimen 4** & **Average Value** \\ \hline Elastic Modulus (E/GPa) & 204.6 & 214.7 & 198.7 & 199.4 & 200.9 \\ Yield Strength (\(f_{y}\)/MPa) & 1778 & 1751 & 1729 & 1724 & 1746 \\ Ultimate Strength (\(f_{u}\)/MPa) & 2017.2 & 2008.2 & 2022.2 & 2015.9 & 2015.9 \\ Fracture Strain (\(\epsilon_{u}\)) & - & 0.045 & 0.056 & 0.051 & 0.051 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Mechanical properties of pre-tension steel cable obtained by strain gauge. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Mechanical Properties** & **Specimen 1** & **Specimen 2** & **Specimen 3** & **Specimen 4** & **Average Value** \\ \hline Elastic Modulus (E/GPa) & 204.6 & 214.7 & 198.7 & 199.4 & 200.9 \\ Yield Strength (\(f_{y}\)/MPa) & 1778 & 1751 & 1729 & 1724 & 1746 \\ Ultimate Strength (\(f_{u}\)/MPa) & 2017.2 & 2008.2 & 2022.2 & 2015.9 & 2015.9 \\ Fracture Strain (\(\epsilon_{u}\)) & - & 0.045 & 0.056 & 0.051 & 0.051 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Mechanical properties of pre-tension steel cables obtained by extensometer. As shown in Figure 13, the arms of the extensometer are ceramic rods with quartz chisel ends, which passed through the side entry port and contacted the test coupons. It is specified for a gauge length of 25 mm and could travel 2.5 mm. Thus, the maximum measurable strain was 10%. During testing, the displacements of the test coupons were directly detected and transmitted by the rods to the strain gauges placed within the extensometer body. A cooling fan was mounted close to the extensometer to maintain the temperature of the extensometer lower than 150 \({}^{\circ}\)C. There were four specimens repeatedly tested in a tensile test to measure the average high temperature stress-strain curve. Two specimens measured by an extensometer, and the other by the CCDC system. The same as for the marker paint process in Section 3.1. For the high temperature test, the high temperature paint was used to make markers on the surface of test specimens. Both the tests measured by the extensometer and CCDC system were conducted on the S690 steel. The target temperature was up to 400 \({}^{\circ}\)C at the heating rate of 10 \({}^{\circ}\)C/min and held for 30 min to obtain uniform temperature distributions in both the furnace and the test specimens.