## 2 Experimental Programs
### Material Properties  
Twenty-four steel standard samples, which were divided into eight groups corresponding to different heating temperatures, were tested for each batch of reinforced and steel tubes. The designed cube compressive strength of commercial concrete produced by China Resources Concrete (Nanning) Co. LTD was 60 MPa. The specific materials were as follows: cement: P-O 42.5 ordinary Portland cement; water; sand: natural river sand; coarse aggregate: crushed stones (5-10 mm); active admixtures: silica fume, slag powder, superplasticizer. Additional details on the materials are given in Table 2. \begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline \hline
**Number** & **Parameter** & **\(b\)/mm** & **\(h\)/mm** & **\(H\)/mm** & **Vertical** & **Stirrups** & **\(d\times\) 8/mm** & **\(\kappa\)** & **\(a\)/mm** & **T\({}^{\prime}\)C** & **\(t\)/min** \\ \hline ZA-1 & \(T\) & 200 & 200 & 600 & 4\(\Phi\)12 & \(\Phi\)6\(\theta\)80 & 114 \(\times\) 3.5 & 0.570 & 20 & 20 & / \\ ZA-1A & \(T\) and \(\kappa\) & 200 & 200 & 600 & 4\(\Phi\)12 & \(\Phi\)6\(\theta\)80 & 89 \(\times\) 3.8 & 0.445 & 20 & 20 & / \\ ZA-1B & \(T\) and \(\kappa\) & 200 & 200 & 600 & 4\(\Phi\)12 & \(\Phi\)6\(\theta\)80 & 138 \(\times\) 3.0 & 0.690 & 20 & 20 & / \\ ZA-2 & \(T\) & 200 & 200 & 600 & 4\(\Phi\)12 & \(\Phi\)6\(\theta\)80 & 114 \(\times\) 3.5 & 0.570 & 20 & 200 & 60 \\ ZA-3 & \(T\) & 200 & 200 & 600 & 4\(\[PERSON]\)12 & \(\Phi\)6\(\theta\)80 & 114 \(\times\) 3.5 & 0.570 & 20 & 300 & 60 \\ ZA-4 & \(T\) & 200 & 200 & 600 & 4\(\Phi\)12 & \(\Phi\)6\(\theta\)80 & 114 \(\times\) 3.5 & 0.570 & 20 & 400 & 60 \\ ZA-5 & \(T\) & 200 & 200 & 600 & 4\(\Phi\)12 & \(\Phi\)6\(\theta\)80 & 114 \(\times\) 3.5 & 0.570 & 20 & 500 & 60 \\ ZA-6 & \(T\) & 200 & 200 & 600 & 4\(\Phi\)12 & \(\Phi\)6\(\theta\)80 & 114 \(\times\) 3.5 & 0.570 & 20 & 600 & 60 \\ ZA-6A & \(T\) and \(\kappa\) & 200 & 200 & 600 & 4\(\Phi\)12 & \(\Phi\)6\(\theta\)80 & 89 \(\times\) 3.8 & 0.445 & 20 & 600 & 60 \\ ZA-6B & \(T\) and \(\kappa\) & 200 & 200 & 600 & 4\(\Phi\)12 & \(\Phi\)6\(\theta\)80 & 138 \(\times\) 3.0 & 0.690 & 20 & 600 & 60 \\ ZA-6-10 & \(T\) and \(a\) & 200 & 200 & 600 & 4\(\Phi\)12 & \(\Phi\)6\(\theta\)80 & 114 \(\times\) 3.5 & 0.570 & 10 & 600 & 60 \\ ZA-6-30 & \(T\) and \(a\) & 200 & 200 & 600 & 4\(\Phi\)12 & \(\Phi\)6\(\theta\)80 & 114 \(\times\) 3.5 & 0.570 & 30 & 600 & 60 \\ ZA-7 & \(T\) & 200 & 200 & 600 & 4\(\Phi\)12 & \(\Phi\)6\(\theta\)80 & 114 \(\times\) 3.5 & 0.570 & 20 & 700 & 60 \\ ZA-8 & \(T\) & 200 & 200 & 600 & 4\(\Phi\)12 & \(\Phi\)6\(\theta\)80 & 114 \(\times\) 3.5 & 0.570 & 20 & 800 & 60 \\ \hline \hline \end{tabular} Note: \(b\), \(h\) and \(H\) are the section width, section height, and length of each column specimen respectively; \(d\) and \(\delta\) are the external diameter and thickness of the inner steel tube, respectively; \(\kappa\) (\(\kappa\) = \(d/b\)) represents the position coefficient of the steel tube; \(a\) denotes the thickness of concrete cover; \(T\) represents the highest temperature of fire endurance; \(t\) denotes the constant temperature time; \(\Phi\) has been used to describe the diameter of the steel bar.  
\end{table} 
Table 1: Design details of each column specimen. According to the standard test method (Chinese code GB/T 50081-2002 [31]), 24,150 mm \(\times\) 300 mm cylinder concrete blocks were reserved and divided into eight groups. At the same time, the concrete standard samples and the column specimens were standing indoors and cured under identical conditions for 28 days. After curing, all specimens (the concrete standard samples, the steel standard samples, and the column specimens) were exposed to high temperature using an RX3-45-9 industrial box resistance furnace at the State Key Laboratory of Engineering Disaster Prevention and Structural Safety, Guangxi University (China). The heating device and measured temperature rise curves are shown in Figure 3. First, all specimens were heated to the design temperature, which was kept constant for 60 min.