Vertical Dynamic Characteristics and Seismic Responses of Prestressed Bridge

Abstract:

Based on the modal perturbation method and the mode superposition method, an approach is established for vertical seismic response analysis of the prestressed bridge. Several problems met in the vertical seismic response analysis of the prestressed bridge are discussed by analyzing two simply-support prestressed bridges. Some conclusions are obtained from the numerical results as follows: ① The natural frequencies increase when the preloading is applied on the bridge. The preloading effect is mainly on the lower natural frequencies and the effect is become smaller when the modal order is higher. The fundament frequency of the prestressed bridges with 20m and 32m span increases about 5.3% and 6.3% respectively and its fifth modal frequency only increases about 1%. ② The moment of middle-span section of the prestressed bridges decreases about 30% and 25% under the excitation of site ground wave. ③ The contributions of high-order modes can be neglected for the vertical seismic responses of the bridges. ④ The ratio factors of the vertical seismic response in the total response of the middle-span section moment of the prestressed bridges are 24.56% and 26.15% when earthquake fortification intensity 7 level and 38.93% and 41.46% when earthquake fortification intensity 8 level respectively. This means that the influence of the vertical responses should be considered in the seismic design of the prestressed bridges.