Dynamic Response Analysis Of Deep-water Composite Piers Under Combined Action Of Earthquake And Wave

Cross-sea deep-water piers that locate in earthquake-prone areas may be subjected to earthquake and wave actions simultaneously in an extreme event.Due to the uncertainty of starting time and direction of earthquake action,the phase difference and skew angle are produced under the combined action.At present,the influence of these two factors on the dynamic response of piers is not clear;In addition,the total hydrodynamic pressure which acting on the pier would not be a simple superposition of individual earthquake and wave actions.So the influence of the coupling effect should be considered in the analysis of the dynamic response.In this paper,the dynamic response of composite piers with different phase difference and skew angle under earthquake and wave actions is analyzed by theoretical derivation,numerical simulation and simplified model.The main research work and creative conclusions are as follows:(1)Based on the extended Morison equation,the theoretical solutions of the structural dynamic response are obtained under the coupling action and the linear superposition action of earthquake and wave.The comparison shows that the size of two is approximately the same,that is,the coupling effect between earthquake and wave has little effect on the dynamic response of the structure.(2)A fluid-structure interaction model of deep-water bridge pier under coupled earthquake-wave action is established to study the influence of phase difference and skew angle on dynamic response of bridge pier.The influence of wave action and coupling interaction on the dynamic response of bridge pier under different phase difference and skew angle are analyzed.The results indicated that both the phase difference and skew angle have significant influence on the dynamic response of the pier,which can reach 73.49% and 69.04% respectively;Wave action may increase or decrease the amplitude of seismic response,and its influence range is much larger than coupling action;When the peak dynamic response is small,the effect of coupling action is large,up to about 25%.On the contrary,when the peak dynamic response is large,the effect of coupling action is less than 10%.(3)Considering the probability combination of phase difference and skew angle,the calculation method of the most unfavorable working condition and its applicable conditions are put forward by using MATLAB software.The results show that the most unfavorable working condition is closely related to frequency of the earthquake excitation,natural frequency under water,structural type and section shape of the pier,but insensitive to PGA of the earthquake and wave height.The concept of coupling coefficient is put forward,which provides a simplified method for calculating the the peak coupled dynamic response of bridge piers under different exceedance probabilities.Through a large number of numerical analysis,it is found that the coupling coefficient fluctuates between 0.9 and 1.1.(4)The simplified analysis method of dynamic response of bridge pier under the combined action of earthquake and wave is established,and the influence of hydrodynamic pressure on the dynamic response of composite piers in elastic and elastic-plastic stage is studied,as well as the applicability of the simplified method under different parameters.The results show that the influence of hydrodynamic pressure is related to the response index,seismic wave type,structure state,wave height and water depth ratio;The error of the simplified method is less than 10%,and its calculation accuracy is related to the structure state,water depth ratio,slenderness ratio of pier and the influence of hydrodynamic pressure.