# Behavior of Circular CFST Columns Subjected to Different Lateral Impact Energy
## 2 Experimental Investigation
### Test Specimens  
The test program is designed to investigate the influence of the parameters on the residual ultimate axial capacity of circular CFST columns subjected to lateral impact. A total of 48 specimens  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Test Coupons**} & **Yield Strength** & **Average Yield** & **Ultimate Strength** & **Average Ultimate** & \multirow{2}{*}{\(f_{\text{y}}\)/\(f_{\text{u}}\)} \\  & \(f_{\text{y}}\) (MPa) & **Strength \(f_{\text{y}}\) (MPa)** & \(f_{\text{u}}\) (MPa) & **Strength \(f_{\text{u}}\) (MPa)** & \\ \hline S1 & 272 & & 353 & & \\ S2 & 263 & 264 & 342 & 352 & 0.75 \\ S3 & 257 & & 361 & & \\ \hline \hline \end{tabular}
\end{table}
Table 1: Properties of steel tube.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline \multicolumn{1}{c}{**Concrete Compressive Strength**} & **Cement (kg)** & **Sand (kg)** & **Coarse Aggregate (kg)** & **Water (kg)** \\ \hline
20 MPa & 350 & 690 & 1160 & 185 \\
30 MPa & 450 & 600 & 1192 & 183 \\
40 MPa & 520 & 525 & 1220 & 178 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Mixed details of different concrete compressive strength.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline \multicolumn{1}{c}{**Nonmal Concrete**} & **Test Coupons** & **Concrete Compressive** & **Average Concrete Compressive** \\
**Compressive Strength (C)** & **Strength \(f_{\text{cu}}\) (MPa)** & **Strength \(f_{\text{cu}}\) (MPa)** \\ \hline  & No.1 & 20.2 & & \\
20 (MPa) & No.2 & 23.6 & 22.13 \\  & No.3 & 22.6 & & \\ \hline  & No.1 & 32.4 & & \\
30 (MPa) & No.2 & 31.6 & 32.70 \\  & No.3 & 34.1 & & \\ \hline  & No.1 & 44.2 & & \\
40 (MPa) & No.2 & 43.5 & 43.13 \\  & No.3 & 41.7 & & \\ \hline \hline \end{tabular}
\end{table}
Table 3: Properties of concrete.  
were fabricated in this test. Three specimens were tested for comparison purpose, and the remaining 45 specimens were tested to evaluate the effect of lateral impact on residual ultimate axial capacity: Details of specimens are shown in Table 4. The height (\(H\)) of all specimens is 300 mm and the external diameter (\(D\)) of cross section of corresponding specimen is 89 mm. Steel tube thickness (\(T\)) used in the test is 4 mm. Regarding to the engineering problem of impact for the CFST columns, the investigated parameters of impact location and impact energy are set to simulate the CFST columns under different impact damage. The impact resistance and failure modes of the CFST columns are investigated to provide some possible method for the reinforcement of the columns. The parameters of concrete compressive strength are also investigated to give some advice for the choice of concrete used in civil engineering project. All tested specimens are labeled according to the parameters so that the specimens can be easily identified. For example, specimen C20-L0.25-E7500 is a steel tube filled with concrete (the concrete compressive strength is 20 MPa of this specimen), which is subjected to 7500 \(J\) impact energy at 0.25 height. The detailed parameters in the study include:  
* Concrete compressive strength (\(C\)): 20 MPa, 30 MPa and 40 MPa;
* Impact location (\(L\)): 0.50 \(H\), 0.33 \(H\) and 0.25 \(H\);
* Impact energy (\(E\)): 5000 \(J\), 7500 \(J\), 10,000 \(J\), 12,500 \(J\) and 15,000 \(J\).  
\begin{table}
\begin{tabular}{c c c c c c c c c} \hline
**Specimen** & \(\mathbf{N^{P}}\) **(MPa)** & \(\mathbf{H}\) **(mm)** & \(\mathbf{D}\) **(mm)** & \(\mathbf{T}\) **(mm)** & \(\mathbf{H}\)/\(D\) & \(\mathbf{D}\)/\(T\) & \(\mathbf{C}\) **(MPa)** & \(\mathbf{L}\) **(H)** & \(\mathbf{E}\) **(J)** \\ \hline C20