# Behavior of Circular CFST Columns Subjected to Different Lateral Impact Energy
## 5 Conclusions  
In this paper, the effects of compressive strength of concrete and lateral impact on the residual ultimate axial capacity of circular CFST columns subjected to lateral impact have been studied. Residual ultimate axial capacity, failure modes, ductility and initial stiffness of circular CFST columns subjected to lateral impact have been analyzed. The following conclusions can be obtained from this test:  
(1) By analyzing the axial compression test process, four kinds of failure modes are summarized in this paper: the first bulged position occurs at the specimen end, which is opposed to the impact point; the first bulged position occurs at the impact point; the bulged position occurs at the impact point, and then deformation is enlarged when the axial compressive load increased. The bulged position occurs at the specimen end, which is opposed to the impact point, and the bulged position develops a ringed bulge as the axial compressive load increased. (2) Lateral impact has negative effects on residual ultimate axial capacity. Residual ultimate axial capacity decreases as impact location gets close to the end of specimen. In addition, improving concrete compressive strength can reduce the negative effects of impact location on residual ultimate axial capacity. \begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline \hline
**Specimen** & \(\mathbf{f_{y}}\) & \(\mathbf{f_{u}}\) & \(\mathbf{f_{cu}}\) & \(\mathbf{\xi}\) & \(\mathbf{\alpha}\) & \(\mathbf{\beta}\) & \(\mathbf{N_{r}}\) & \(\mathbf{N_{re}}\) & \(\mathbf{\rho}\) & **Error** \\  & **(MPa)** & **(MPa)** & **(MPa)** & **(MPa)** & **(**\(\mathbf{\beta}\)**)** & **(kN)** & **(kN)** & **(N\({}_{re}\)/\(N_{r}\))** & **(\%)** \\ \hline C30-L0.25-E12500 & 264 & 352 & 32.70 & 1.70 & 0.25 & 2.50 & 510.25 & 471.49 & 0.92 & \(-8\) \\ C30-L0.25-E15000 & 264 & 352 & 32.70 & 1.70 & 0.25 & 3.00 & 479.70 & 458.65 & 0.96 & \(-4\) \\ C40-L0-E0 & 264 & 352 & 43.13 & 1.29 & – & – & 595.00 & – & – & – \\ C40-L0.50-E5000 & 264 & 352 & 43.13 & 1.29 & 0.50 & 1.00 & 648.80 & 604.52 & 0.93 & \(-7\) \\ C40-L0.50-E7500 & 264 & 352 & 43.13 & 1.29 & 0.50 & 1.50 & 598.95 & 588.69 & 0.98 & \(-2\) \\ C40-L0.50-E10000 & 264 & 352 & 43.13 & 1.29 & 0.50 & 2.00 & 579.50 & 579.38 & 0.99 & \(-1\) \\ C40-L0.50-E12500 & 264 & 352 & 43.13 & 1.29 & 0.50 & 2.50 & 576.75 & 563.02 & 0.98 & \(-2\) \\ C40-L0.50-E15000 & 264 & 352 & 43.13 & 1.29 & 0.50 & 3.00 & 569.00 & 547.66 & 0.96 & \(-4\) \\ C40-L0.33-E5000 & 264 & 352 & 43.13 & 1.29 & 0.33 & 1.00 & 575.25 & 564.09 & 0.98 & \(-2\) \\ C40-L0.33-E7500 & 264 & 352 & 43.13 & 1.29 & 0.33 & 1.50 & 526.25 & 556.01 & 1.06 & 6 \\ C40-L0.33-E10000 & 264 & 352 & 43.13 & 1.29 & 0.33 & 2.00 & 600.85 & 540.38 & 0.90 & \(-10\) \\ C40-L0.33-E12500 & 264 & 352 & 43.13 & 1.29 & 0.33 & 2.00 & 560.00 & 528.39 & 0.94 & \(-6\) \\ C40-L0.33-E15000 & 264 & 352 & 43.13 & 1.29 & 0.33 & 3.00 & 540.10 & 513.71 & 0.95 & \(-5\) \\ C40-L0.25-E5000 & 264 & 352 & 43.13 & 1.29 & 0.25 & 1.00 & 475.75 & 547.62 & 1.15 & 15 \\ C40-L0.25-E7500 & 264 & 352 & 43.13 & 1.29 & 0.25 & 1.50 & 650.00 & 536.79 & 0.83 & \(-17\) \\ C40-L0.25-E10000 & 264 & 352 & 43.13 & 1.29 & 0.25 & 2.00 & 460.25 & 525.67 & 1.14 & 14 \\ C40-L0.25-E12500 & 264 & 352 & 43.13 & 1.29 & 0.25 & 2.50 & 622.15 & 508.82 & 0.82 & \(-18\) \\ C40-L0.25-E15000 & 264 & 352 & 43.13 & 1.29 & 0.25 & 3.00 & 600.00 & 497.83 & 0.83 & \(-17\) \\ \hline Mean value & & & & & & & & & 0.97 & \(-3\) \\ Minimum value & & & & & & & & & 0.82 & \(-18\) \\ Maximum value & & & & & & & & & 1.38 & \(-38\) \\ Variance & & & & & & & & & & & 0.0136 & 0.0136 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: _Cont._  
Figure 17: Statistic result of \(\lambda\). (3) Ductility and initial stiffness of the specimens are affected by lateral impact. Initial stiffness and ductility decrease when impact energy increases. Initial stiffness and ductility decrease when impact location gets close to the specimen end.