# Seismic Effectiveness of Multiple Seismic Measures on a Continuous Gider Bridge
## 5 Calculation Analysis and Discussion  
### Displacement of Girders, Bearings, and Pier Top  
The seismic performances of more than 10,000 continuous girder bridges have been evaluated using a modal response spectrum analysis of a detailed finite-element model. The results indicate a considerable influence of the longitudinal ground motion component on the overall response [50]. Therefore, this paper mainly analyzes the longitudinal seismic response of bridge structures. The longitudinal displacement of the girder of the bridge structure is the critical parameter to evaluate the seismic safety of the bridge. The excessive longitudinal displacement of the girder will cause seismic hazards, such as bridge population, unseating, etc. Different levels of seismic loads were applied to the bridge structures with six different cases for seismic measures (Figure 5). Figure 7 shows the displacement of the girder after different cases for seismic measures were used in earthquakes of different magnitudes. It can be seen in Figure 7 that, in different cases, with an increasing magnitude of the earthquake, the displacement of the girder increases, with significant changes in the Northridge earthquake. However, the displacement of the girder basically does not change under the action of a  
Figure 6: Models and results: (**a**) experimental model, (**b**) analytical model, (**c**) seismic response under El Centro earthquake, (**d**) seismic response under Northridge earthquake, (**e**) error analysis of the test and numerical simulation (El Centro earthquake), and (**f**) error analysis of the test and numerical simulation (Northridge earthquake). small earthquake in different cases. In Cases 1 and 2, the displacement of the girder end of the bridge structure exceeds the initial gap--16 cm--of the bridge expansion device under the action of large and Northridge earthquakes, leading to impact and damage at the expansion device. It was also found that the displacement of the girder is close to or more than 16 cm under the action of the large earthquake in Case 3 and the Northridge earthquake in Case 4. It should be noted that the displacement of the bridge girder under the action of the Northridge earthquake is less than or close to that under the action of the large earthquake in Cases 2 and 3, which is also observed in Cases 5 and 6. That may be due to the fact that the displacement of the bearing is not controlled by the unseating prevention devices until its displacement reaches its shear deformation in Case 4 without a restrainer, so the structure is subjected to a large earthquake impact force. The unseating prevention devices have a higher impact on the structural response under the action of a large earthquake than the Northridge earthquake. It is worth mentioning that the displacement of the bridge girder is less than 16 cm at earthquakes of different magnitudes in Cases 5 and 6. This means that the cooperation of the restrainer and unseating prevention devices can effectively avoid bounding and unseating damage. However, in Case 1, the largest displacements of the bridge girder without seismic measures are 14.99 cm, 19.12 cm, and 24.92 cm, respectively, under the action of moderate, large, and Northridge earthquakes, suggesting that the bridge girder can be protected to different extents only when seismic measures are taken. The excessive deformation of the bearing in the bridge structure directly causes bearing failure and unseating damage. The displacement is an important index to evaluate the failure of the bearing. In this study, sliding rubber bearings were used for #1 and #5 piers of the bridge, while laminated rubber bearings were used for #2, #3, and #4 piers. Thus, the maximum displacement of the sliding rubber bearings and plate rubber bearings under the action of the earthquake was summarized as the control object. Figure 8 shows the change of the bearing displacement of the bridge structure with different seismic measures.