# Seismic Effectiveness of Multiple Seismic Measures on a Continuous Gider Bridge
## 6 Conclusions  
In this paper, the dynamic time history analysis of a four-span continuous girder bridge is carried out for earthquakes of different magnitudes. The large displacement of bridge bearings and expansion joints under the action of a large earthquake leads to seismic hazards, such as unseating, bounding, and collapse, so seismic measures were proposed to improve the seismic performance of the bridge in this paper. The restrainer and unseating prevention devices have different displacement control ranges, and the seismic effect of the expansion device should not be ignored. Thus, six different combinations of seismic measures were taken for the bridge in order to discuss the mechanical behaviors of the bridge structure, including the seismic performance structural displacement, the bending moment of piers, etc., and we comparatively analyzed the seismic effect of several combinations of seismic measures in this study. The following are the main conclusions of this study:  
1. Under larger earthquakes, the initial design of the bridge (Case 1) was found to be damaged by bearing failure, bounding, expansion device failure, and collapse damages without the prevention of seismic measures. For the expansion joint, its maximum displacement--24.92--was much more than its design displacement--16 cm--under the action of the Northridge earthquake. The sliding rubber bearings and laminated rubber bearings have a maximum displacement of 23.78 cm and 19.38 cm, respectively, which are more than their shear deformation of 8.12 cm and 9.1 cm, respectively. The maximum bending moment, 32,594 kN-m, at their bottoms of #2, #3, and #4 piers with laminated rubber bearings is four times the maximum bending moment, 7564 kN-m, at the bottoms of #1 and #5 piers with sliding rubber bearings. The seismic load is unevenly distributed between the piers, leading to a great difference in displacement at the top of each pier. 2. Damping expansion devices can weaken the seismic response of the bridge slightly; restrainers can effectively reduce the displacement of the bridge and improve the overall stiffness of the bridge under small and moderate earthquakes. However, if the seismic magnitude exceeds a moderate earthquake, the restrainer cannot be effectively limited to the excessive displacements of the bridge. The combination of the restrainer and unseating prevention was found to be more effective at controlling the excessive displacement of the bridge. The expansion joint and bearing have a maximum displacement reduction of 48% and 34%, respectively. As the displacements of bearings and expansion joints were reduced within their allowable deformation, the bridge was prevented from bounding and collapse during earthquakes. In addition, the moment at the bottom and the displacement at the top of #1 and #5 piers greatly increased, and even slightly exceeded those of #2, #3, and #4 piers; however, all the piers have a similar seismic response, and the seismic load is uniformly distributed between the piers. 3. Under the action of the earthquake, a large displacement occurs to the sliding rubber bearings (#1 and #5 piers), so a smaller seismic load is transferred to #1 and #5 piers. Thus, #2, #3, and #4 piers have a bigger maximum displacement and bending moment than #1 and #5 piers. The restrainer and installed unseating prevention devices increase the connection stiffness between the substructure and superstructure of the bridge with #1 and #5 piers, distribute a bigger seismic load to the substructure, and increase the displacement at the top and bending moment at the bottom of #1 and #5 piers by a factor of more than four compared with the preliminary design. This revealed that seismic measures could increase the overall stiffness of the bridge and more evenly distribute the impact force and seismic energy among piers caused by earthquakes. 4. Under the action of the large and Northridge earthquakes, there is a big impact force at the expansion joint of the bridge.