# Seismic Effectiveness of Multiple Seismic Measures on a Continuous Gider Bridge
## 5 Calculation Analysis and Discussion
### Internal Force
#### 5.3.2 Internal Force of Seismic Measures  
In this paper, each seismic measure plays a vital role in restraining the excessive displacement of the structure and bears the seismic load in an earthquake. Table 3 shows the internal force peak value of seismic measures in each case under earthquakes of different magnitudes. In Case 2, the expansion device has no large load, but only the rubber embedded in the expansion joint produces a small damping force under the action of small and moderate earthquakes. Under the action of large and Northridge earthquakes, the expansion device has a bigger internal force than its ultimate impact force of 15,000 kN. In Case 3, the restrainer starts to bear the force under the action of the small earthquake; with increasing force, its internal force increases under the action of moderate and large earthquakes. The sliding rubber bearing has a smaller displacement, and the restrainer has a smaller internal force under the action of the Northridge earthquake than the large earthquake; the expansion device has the maximum internal force of 28,973 kN under the action of the large earthquake. In Case 4, the expansion device hardly bears a force when the unseating prevention devices are installed [53]. The unseating prevention devices do not start under the action of the small earthquake. The internal force of the unseating prevention devices increases gradually under the action of moderate, large, and Northridge earthquakes. However, the maximum internal force (3691 kN) of the unseating prevention devices exceed its design breaking force, 3340 kN, under the action of the Northridge earthquake. In Case 5, the function of the expansion device is not taken into account; the restrainer and the unseating prevention devices are applied together. The unseating prevention devices do not start under the action of the small earthquake, and the internal forces of the restrainer and unseating prevention devices increase under the action of moderate and large earthquakes. The internal forces of the restrainer and the unseating prevention devices are slightly smaller under the action of the Northridge earthquake than the large earthquake. The internal forces of the restrainer and the unseating prevention devices are smaller in Case 5 than Cases 3 and 4. For the restrainer under the action of the large earthquake, its internal force, 594 kN, can reduce to about half of its internal force, 1209 kN, without a coupling device. For the unseating prevention devices, their internal force is also much smaller than that when they are used alone and does not exceed its design breaking force. This means that the cooperation between the restrainer and unseating prevention devices is very beneficial to the forces on the two measures, reducing the internal force and playing a specific protective role under the action of an earthquake. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline  & **Seismic Measures** & \begin{tabular}{c} **Small** \\ **Earthquake** \\ \end{tabular} & \begin{tabular}{c} **Moderate** \\ **Earthquake** \\ \end{tabular} & \
\begin{tabular}{c} **Large** \\ **Earthquake** \\ \end{tabular} &
\begin{tabular}{c} **Northridge** \\ **Earthquake** \\ \end{tabular} \\ \hline Case 2 & Expansion devices & \(1\) & 3 & 30,301 & 29,973 \\ \hline \multirow{2}{*}{Case 3} & Expansion devices & \(1\) & 3 & 28,973 & 4 \\ \cline{2-6}  & Restrainer & 49 & 582 & 1209 & 941 \\ \hline \multirow{2}{*}{Case 4} & Expansion devices & \(1\) & 3 & 5 & 5 \\ \cline{2-6}  & Unseating prevention device & 0 & 1814 & 3213 & 3691 \\ \hline \multirow{2}{*}{Case 5} & Restrainer & 52 & 511 & 594 & 544 \\ \cline{2-6}  & Unseating prevention device & 0 & 703 & 2587 & 1461 \\ \hline \multirow{2}{*}{Case 6} & Expansion devices & 1 & 3 & 5 & 3 \\ \cline{2-6}  & Restrainer & 49 & 509 & 593 & 548 \\ \cline{2-6}  & Unseating prevention device & 0 & 667 & 2589 & 1556 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Maximum internal force of seismic measures under different earthquakes.