Analysis of factors influencing seismic responses of ramp bridges

To probe into the laws of influences of the geometry irregularities of ramp bridges on the seismic responses of the bridge structures, a finite element analysis model for the structures was established, using the software SAP2000 based on the example of a ramp bridge on the Jiamin Elevated Road Line and the seismic responses of the ramp bridges under the different span arrangement, longitudinal slopes, curvature radii and ground motion input directions were analyzed. The results of the analysis show that as compared with a simply-supported beam bridge, the multi-span continuous beam bridge can have significant increase of the seismic responses in the fixed piers in the longitudinal direction and in the low piers and transition piers in the transverse direction. The influences of the longitudinal slope changes on the longitudinal seismic responses of the ramp bridges are slight, however, the arrangement of the heavy slopes in the transverse direction is helpful to the alleviation of the seismic responses of the columns in the high pier area. Under the sharp curvature radii of the ramp bridges, the angle deviations exist between the ground motion input in the tangential and normal directions and the worst ground motion input direction, which may lead to the underestimation of the seismic responses of the structures. Under the gentle curvature radii, the seismic responses of the curved ramp bridges are basically consistent with those of the straight ones and the ramp bridges can be simplified as the straight ones for analysis. ©, 2015, Wuhan Bridge Research Institute. All right reserved.