| With the construction of a large number of offshore engineering projects,the seismic performance and safety of offshore structures have received widespread attention.Although existing research has found significant differences in seismic characteristics between the offshore and land,strong earthquakes on land are still commonly used in seismic design of offshore structures.In order to realize the application of offshore ground motion in the seismic analysis of offshore structures,it is necessary to systematically study the characteristics of offshore ground motion.In this paper,the measured strong motion records on the offshore are taken as the research object,and the correlation analysis of existing records is carried out using statistical methods.The elastic and elastoplastic response spectrum characteristics of offshore ground motions with different focal mechanisms are systematically studied.On this basis,the influence of seismic source mechanism on the seismic response of cross sea bridges was further analyzed.Finally,this article discusses the site conditions and characteristics of offshore strong earthquake stations in the K-net network of Japan,and attempts to propose the attenuation law of seismic motion in the offshore area.The specific work content is as follows:(1)This paper briefly introduces the research status and shortcomings of the characteristics of offshore ground motion,and collects and classifies the strong motion records collected by the offshore strong motion stations in the Xiangmo Bay,Japan.The differences of correlation spectrum characteristics of offshore ground motions under different focal mechanisms are analyzed and compared.(2)Using the finite element analysis software MIDAS used in the seismic design of practical projects,the model of the cross sea vibration isolation continuous beam bridge is established,and the records of the offshore strong earthquakes with different focal mechanisms under limited conditions are input respectively.By comparing the seismic responses of the bridge pier top displacement,acceleration,and pier bottom stress under different working conditions,the seismic response characteristics of the bridge under the action of the offshore ground motions with different focal mechanisms are determined.(3)The study proposes a seismic wave response method that considers the coupling of seawater soil layer cross sea beam bridges.By inputting strong earthquake records of bedrock with different focal mechanisms,the seismic response characteristics of cross sea bridges under the coupling effect of focal mechanisms and offshore sites are analyzed.(4)In order to propose the prediction equation of regional offshore ground motion,this paper uses the H/V spectrum ratio method,response spectrum shape analysis method and attenuation law method to analyze the site conditions of the offshore location of strong motion stations in Xiangmo Bay sea area,and attempts to group them.(5)On the premise of considering the source mechanism of the offshore ground motion and the site type of the station,the elastic response spectrum prediction model of the horizontal offshore ground motion in the Xiangmo Bay area of Japan is established through the random forest method,and the prediction equation of the horizontal offshore ground motion in the Xiangmo Bay area is proposed. |
