Stochastic Dynamic Response Analysis of Bridge Piers in Deep Water Under Combined Earthquake and Wave Actions

Abstract eng:
Earthquake and wave actions may be simultaneously applied to bridge piers in deep water. It is necessary to calculate the dynamic response of bridge piers under combined earthquake and wave actions. In order to consider the randomness of earthquake and wave action, stochastic dynamic response analysis is adopted. The interaction between bridge piers and water can be considered into two parts: the hydrodynamic pressure and wave action. Since most bridge piers belong to large-scale cylinder, the hydrodynamic pressure is established using radiation wave theory, and the wave action is considered by the diffraction theory. Based on the pseudo excitation method, a stochastic dynamic analysis method for bridge piers in deep water under combined actions of earthquake and wave is developed. A circle solid pier is calculated with a sectional diameter of 5 m and a height of 24.7 m. The Clough-Penzien spectrum is used as the earthquake acceleration spectrum and the Bretschneider-Mitsuyasu spectrum is used as the wave height spectrum. Stochastic dynamic responses of bridge piers under the earthquake action, wave action and combined actions of earthquake and wave, are analyzed respectively. Different relative water depths and earthquake acceleration amplitudes are considered for the analysis of the numerical model under earthquake action. While the model under wave action is caculated, different wave heights and relative water depths are analyzed and compared. Moreover, in order to compare with the response under combined earthquake and wave actions, the response under the direct superpositon of two individual actions should be achieved. The results show that the stochanic dynamic response of the pier in deep water is increasing because of the influence of the hydrodynamic pressure. For a pier with a fixed water depth under different earthquake acceleration amplitudes, the increased percentage of the internal force power spectrums at the bottom of piers is identical, considering the effect of the hydrodynamic pressure. With relative water depth becoming deeper, the effect of the hydrodynamic pressure to the internal force power spectrums at the bottom of the pier becomes more significant. Because the attached mass generated by the pier’s elastic motion in the water has little effect on the frequency response function of the pier, stochanic dynamic responses under combined earthquake and wave actions are identical with these under the direct superposition of two individual actions.

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