Study On The Influence Of Offshore Ground Motion And Site Factors On The Seismic Response Of Piers

Compared with onshore bridges,the site environment and ground motion characteristics of sea-crossing bridges are quite different.These factors cannot be ignored in the seismic design of sea-crossing bridges.Among them,the use of onshore or offshore ground motion as seismic load in the seismic response analysis of sea-crossing bridges,and the influence of seabed site factors and hydrodynamic effects on the seismic response and damage characteristics of bridges are two key issues to be solved in the field of bridge seismic field.In view of the above scientific problems,shake table tests are an effective and direct research method to understand the seismic performance of structures,but it is difficult to carry out due to the limited test conditions and high budget.In view of the mature application of the refined analysis model of seismic response of piers and other components,this paper attempts to study the seismic response and damage characteristics of bridges under the influence of offshore ground motion characteristics and seabed site factors through numerical experiments.In this paper,the reinforced concrete piers model are established based on the finite element dynamic analysis software ABAQUS,and the numerical model is verified by the quasi-static and shake table tests of piers completed by previous scholars.Secondly,the numerical test method is used to study the seismic response and damage characteristics of common reinforced concrete piers under different peak acceleration offshore and onshore strong ground motion records.Thirdly,the numerical test model of underwater shake table is established by using the dynamic analysis software ADINA,and the influence of water layer depth and seabed cover on the seismic response of piers are analyzed.Finally,based on the above researches,the influence of hydrodynamic pressure on the response of piers with different diameters and shapes are further analyzed.The influence of boundary conditions of numerical model on structural response is discussed.The specific research conclusions obtained in this paper are as follows :(1)Due to the horizontal response spectrum of the offshore ground motion is higher than the onshore ground motion in the medium and long period,the seismic response of piers under the action of the offshore ground motion are generally greater than the onshore ground motion in the numerical test.When the seismic intensity is low,the dynamic response difference between offshore and onshore seismic excitation are small,but with the increase of the peak acceleration of the input acceleration time history,the response of the structure under the action of the offshore ground motion is significantly greater than the onshore ground motion input.(2)The existence of water and soil have a certain influence on the seismic response of piers.When the water level is low,the influence of the water depth on the dynamic response of the structure is not obvious,but as the water depth increases,the seismic response of piers becomes more intense.The interaction between soil depth and structure will reduce the natural vibration frequency of the structure,increase the natural vibration period and damping,constrain the bottom of piers,and reduce the dynamic response of piers.(3)Under different peak acceleration earthquakes,the influence of piers size,section form and fluid boundary type on the hydrodynamic pressure of piers are basically the same.In the numerical test,the peak value of hydrodynamic pressure under seismic load increases with the increase of water level depth.When the water level is low,the change of piers size,section form and fluid outer boundary have little effect on the hydrodynamic pressure of piers,but with the increase of water level,the influence of various factors are slightly reflected.