# Seismic Analysis of Steel Solid Web Girder-RC Tubular Column Hybrid Structure
## 4 Numerical Results and Discussion
### Lateral Stiffness Deterioration and Damage Analysis  
Table 5 summarizes the numerical results of maximum stresses of A-shaped steel frames, steel braces and steel solid web girder under different hazard levels, as shown in Figure 11. It can be observed that the steel components of steel solid web girder-RC tubular column hybrid structure did not yield under the earthquakes. Figure 12 shows the damage distribution patterns of the RC tubular columns under different hazard levels. It can be seen that the damage mainly occurred on the bottom of the RC tubular column, lower part of the corbel, and upper part of the corbel. This phenomenon is similar with the experimental result of the steel braced truss-RC tubular column hybrid structure and the failure mechanism has been clarified through mechanical analysis [14]. Generally, in the seismic design, the failure hierarchy criterion strong column-weak beam is applied. The aim of the proposed procedure is the earlier development of yielding in beams rather in columns [28; 29; 30]. However, for the structure described in this paper, the damage mainly occurred on the columns while the steel components did not yield. In fact, this coincided with the expected design results. Since the steel solid web girder platform and A-shaped frames must bear the important industrial units directly in practical engineering, if the steel components yield untimely, the normal use of the industrial units would be affected. Accordingly, they are expected to suffer negligible damage under earthquakes. In addition, as the key components to improve the overall stiffness and structural integrity, the steel diagonal braces should be designed strong enough.  
Figure 11: Maximum stresses of the steel components under different hazard levels.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Hazard Level (PGA)** & \begin{tabular}{c} **A-Shaped** \\ **Frame** \\ \end{tabular} & \begin{tabular}{c} **Solid Web** \\ **Girder** \\ \end{tabular} & \
\begin{tabular}{c} **Brace of Solid** \\ **Web Girder** \\ \end{tabular} &
\begin{tabular}{c} **Steel Diagonal** \\ **Brace** \\ \end{tabular} \\ \hline Frequent earthquake (0.07 g) & 72 & 98 & 88 & 115 \\ Basic earthquake (0.20 g) & 112 & 156 & 117 & 173 \\ Rare earthquake (0.40 g) & 167 & 211 & 144 & 243 \\ Very rare earthquake (0.62 g) & 207 & 253 & 167 & 276 \\ \hline \hline \end{tabular}
\end{table}
Table 5: Maximum stresses of steel components under different hazard levels (MPa).  
Figure 13 shows the changing rules of relative stiffness ratios and maximum damage indexes with increase of the PGA. It can be found that the lateral stiffness of solid web girder-RC tubular column hybrid structure under the very rare earthquake was still 39% of the initial stiffness, although the stiffness deteriorated significantly with increase of the PGA. In addition, it can be observed that the maximum tensile damage index was 0.90 under the very rare earthquake (PGA = 0.62 g), indicating that the structure was severely damaged but did not collapse. Overall, the numerical results showed that the steel solid web girder-RC tubular column hybrid structure could satisfy the seismic design requirements under the four hazard levels.  
Figure 12: Damage distribution of RC tubular columns subjected to different hazard levels: (**a**) Tensile damage under basic earthquakes; (**b**) tensile damage under rare earthquakes; (**c**) tensile damage under very rare earthquakes; (**d**) compressive damage under very rare earthquakes.  
Figure 13: Relative stiffness ratios and maximum damage indexes under different hazard levels.