# Seismic Response Analysis of a Curved Bridge under Near-Fault and Far-Field Ground Motions
## 4 Test Results
### Displacement of Mid-Span  
Figure 8 shows the mid-span displacement of the curved bridge in the excitation of near-fault and FF ground motions. When the connecting direction of the two abutments is the same as the EW-direction, the second span produces the largest mid-span displacement in the excitation of \(X_{\rm P}\), while the third span has the smallest mid-span displacement. Given that fixed pot bearings are arranged at pier 2, the curved bridge rotates in the plane while moving horizontally, and the seismic force increases the displacement at the first mid-span through the fixed pot bearings. The mid-span displacement of the curved bridge in the  
Figure 6: Acceleration spectrum of selected g seismic waves. (**a**) Acceleration response spectrum of the EW component; (**b**) Acceleration response spectrum of the NS component.  
excitation of NP and NN ground motions increases by 82.4% (tangential displacement) and 22.8% (radial displacement) compared with that in the excitation of FF ground motions. When the NP ground motion is excited by \(\rm X_{P}+Y_{S}\), the tangential mid-span displacement is significant in the first span. Meanwhile, under the NN and FF ground motions, the displacement is larger in the third span. This result indicates that the bidirectional seismic excitation of NP seismic records stimulates the in-plane rotations of the bridge model. The mid-span displacement of the curved bridge for NP and NN ground motions increases by 135.6% (tangential displacement) and 17.9% (tangential displacement) compared with that for FF ground motions.  
When the connecting direction of the two abutments is the same as the NS-direction, the mid-span displacements of the third span in the excitation of \(\rm Y_{P}\) and \(\rm X_{S}+Y_{P}\) are larger than those of the first span. The seismic input in the transverse bridge direction (Y-direction) makes the curved bridge mainly move horizontally, resulting in a smaller plane rotation. Compared with the mid-span displacement of the curved bridge for FF  
Figure 8: Mid-span displacement response in the excitation of near-fault and FF ground motions: (a) Mid-span displacement response in case 1; (b) Mid-span displacement response in case 2.  
Figure 7: Mode shapes of the shaking table test model: (a) First mode, f1 = 2.55 Hz; (b) Second mode, f2 = 3.31 Hz; (c) First mode, f3 = 5.70 Hz; (d) First mode, f4 = 13.52 Hz.  
ground motions, the mid-span displacement in the excitation of \(\rm Y_{P}\) is increased by 112.9% and 29.6% (tangential displacement) for NP and NN ground motions, respectively; in the excitation of \(\rm X_{S}+Y_{P}\), the mid-span displacement increases by 90.6% and 17.1% (tangential displacement), respectively.  
When the connecting direction of the two abutments is the same as the EW-direction, the motion state of the main girder has a spatial effect due to the excitation of ground motions. In the excitation of \(\rm X_{P}\), the curved bridge generates rotation in the plane; in the excitation of \(\rm X_{P}+Y_{S}\), especially the NP ground motion excitation, the curved bridge rotation in the plane can also be stimulated. When the connecting direction of the two abutments is the same as the NS-direction, the whole curved bridge is mainly translational, indicating that the motion state of the main girder is related to the excitation mode of the seismic waves. The mid-span displacement in the excitation of NP and NN ground motions increases significantly. Particularly, it increases the most in the excitation of NP ground motions, implying that the NP ground motions are more destructive.