## 4 Lattice Composite Tower and Damping System
### Experimental Verification of Scheme Feasibility  
To verify the scheme feasibility of the proposed lattice composite tower and damping system, a shaking-table test of a scaled bridge tower model was then performed, as shown in Figure 12. Limited by shake-table size, the effect of the suspension cable and bridge deck system on the seismic response of bridge tower were not considered in this test. However, through the shake-table tests, a comparison of the dynamic characteristics as well as the seismic response between the original main tower and lattice composite tower could still be directly obtained. In this test, the original tower was manufactured using steel sheets with a thickness of 2.5 mm. The yielding strength was 345 MPa. The overall height of the main tower was 3.119 m. The cross-sections of the main tower were 153 mm \(\times\) 153 mm and 80 mm \(\times\) 80 mm at the bottom and top, respectively. Mass blocks of 50, 50, 40, 40, 40 and 50 kg were located at heights of 0.62, 1.12, 1.62, 2.12, 2.62 and 3.03 m, respectively. For the  
Figure 11: Detail of lattice composite tower.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Model**} & **Single Tower** & **Lattice Composite Tower** & \multicolumn{2}{c}{**Lattice Composite Tower with**} \\  & **(Hz)** & **(Hz)** & **Friction Damper** \\ \hline
1 & 0.055 & 0.056 & 0.057 \\
2 & 0.089 & 0.092 & 0.094 \\
3 & 0.100 & 0.102 & 0.102 \\
4 & 0.104 & 0.105 & 0.106 \\
5 & 0.126 & 0.132 & 0.134 \\
6 & 0.134 & 0.146 & 0.149 \\
7 & 0.145 & 0.147 & 0.149 \\
8 & 0.146 & 0.151 & 0.153 \\
9 & 0.150 & 0.153 & 0.154 \\
10 & 0.156 & 0.157 & 0.158 \\ \hline \hline \end{tabular}
\end{table}
Table 3: Frequencies of the super-long-span suspension bridge.  
lattice composite tower scheme, the height of the four separate sub-towers was identical to the original tower. The cross-section of each sub-tower was 81 mm \(\times\) 81 mm at the bottom. At the top, the cross-section was changed to 50 mm \(\times\) 50 mm. These four sub-towers were located at the four corners of a square, with a cross-section of 220 mm \(\times\) 220 mm. The mass blocks were equally distributed at the same height in the four sub-towers. The sub-towers were connected together with four connecting beams at the top.  
Typical earthquake records were chosen to evaluate the seismic performance of the lattice composite tower, including the El Centro earthquake with a PGA of 580 gal. The seismic response at the tower top is shown in Figure 13. The results indicated that the lattice composite tower markedly decreased the displacement response at the tower top and improved the seismic performance of the super-long-span suspension bridge. These seismic reduction effects of the tower top displacement agreed well with the results in reference [15]. In addition, the control effect of the tower top displacement by viscous damping system could reach over 46%, which is close to the results in reference [31].  
Figure 12: Test specimen of original main tower and lattice composite tower: (**a**) original main tower; (**b**) lattice composite tower.  
Figure 13: Comparison of seismic responses at the tower top between original main tower and lattice composite tower: (**a**) acceleration response; (**b**) displacement response.