Study On Seismic Response Of Offshore Bridge Considering Multi-medium Coupling

In view of the special hydrological and geological conditions of offshore bridges,a three-dimensional water-soil free field model is established by OpenSEES software based on the saturated artificial boundary and the wave input method of ground motion.The influence of overlying water layer on the seismic response of free field is studied,and the special environmental factors affecting the liquefaction of saturated foundation and the dynamic pressure of offshore deep water bridges are studied.The water-bridge global model and water-saturated soil-bridge integral model are established,respectively,which are compared with the anhydrous model and the non-liquefaction model.The seismic response of an offshore bridge subjected to wave load,seismic load and combined load is studied.The parallel algorithm of OpenSEES based on GPU is used to calculate the water-saturated soil-bridge system.The influence of site liquefaction on bridge seismic response is studied.The main work and corresponding results of this paper are as follows:(1)Based on the equivalent artificial boundary,the model of water-soil free field is established by OpenSEES software,and compared with the model of anhydrous,and it can be found that the seismic response of the free site with overlying water under different incident angles and water depth is studied.The effect of water layer on P wave is greater than that of SV wave.Under the action of P wave,the displacement peak and acceleration peak of water soil free field are smaller than that of anhydrous free field,and there is a certain delay in the appearing time of water layer,but under the action of SV wave,the water layer has little effect on the seismic response of the site.When P-wave is vertically incident into the free field of deep-water and soil-water,the influence of water depth on the peak displacement is very small,and the acceleration peak is greatly affected by the increase of water depth,and the acceleration peak decreases rapidly and then slows down with the increase of water depth.(2)In the background of an offshore bridge,the dynamic water pressure is considered based on the Morison equation method,and the incident wave force is calculated by using the modified linear wave theory.The dynamic response of the bridge under the wave load,the seismic load acting alone and the combination action is studied.Research showing that he dynamic response of the bridge under the action of wave load is very small,and the response value of the bridge presents a similar sinusoidal curve change,and the response frequency of the bridge is similar to that of the wave frequency.The peak response of the bridge under the action of the wave along the longitudinal bridge is larger than that of the transverse bridge.Considering the added mass of the nderwater part of the pier,the natural frequencies of the bridge are all reduced,and the existence f hydrodynamic pressure increases the dynamic response of the pier,which is related to the(?)ading direction of the seismic wave.The response value of earthquake and wave interaction is ot the simple superposition of the response value under the two separate actions,and the istribution law is complex.(3)Based on the computer configuration of the existing workstations,the seismic response f water-saturated soil-bridge system is calculated by using the high performance solution of GPU,nd the seismic response of the bridge considering site liquefaction condition and not is compared ynthetically.It can be seen that the seismic response of liquefaction site is related to the input requency spectrum of seismic wave.The increase of liquefaction degree will increase the peak alue of soil dynamic response and increase the spreading depth of liquefaction soil area.The iquefaction site increases the seismic response of the bridge,the peak displacement of the pier ppears lag phenomenon under the condition of site liquefaction,the displacement of the pier top xists some residual value after the earthquake,and the effect of site liquefaction on the shearing brce of the pier bottom is greater than that of the bending moment.The liquefaction site ignificantly increases the lateral deformation of pile foundation,and the most significant increase s at the top of the pile.The liquefaction of the site also increases the displacement value of the(?)ean,and the increase of the displacement at the end of the beam may lead to the risk of collision(?)r fall of the bridge beam,which should be paid more attention to.