Study On Dynamic Response Of Offshore Continuous Beam Bridge Structures Under Extreme Wave And Scour

The global climate change has resulted in the expansion of ocean water and the melting of polar ice,leading to a rise in sea level and more frequent occurrences of extreme weather,which in turn increases the frequency and intensity of typhoons and hurricanes.The severe weather,such as typhoons and hurricanes,can cause extreme waves and pose a significant threat to the safety of nearshore engineering structures.Extreme waves,scour,storm surges,etc.,are the main reasons for bridge damage caused by typhoons and hurricanes.Scholars have conducted extensive research on the dynamic response and bearing capacity of bridge structures under the influence of single factors such as extreme waves and scour,but few studies have considered the combined effect of extreme waves and local scour.This article selects a three-span continuous beam bridge near the coastal area as the research object,considering the influence of extreme wave characteristics,scour depth,soil and structure interaction,and other factors.The fluid-structure interaction method is used to study the mechanism and law of structural dynamic response of the bridge under the joint effect of extreme waves and local scour.Anumerical wave flume model based on computational fluid dynamics software has been established to reveal the propagation characteristics of nonlinear waves in a flume.The model has been compared and analyzed with results obtained from water wave theories and physical flume experiments.The effective error of the wave height generated by the numerical wave flume is less than 5.0%,indicating that the effective wave height and wave loads on obstacle surfaces generated by the numerical wave flume meet engineering accuracy requirements and exhibit good stability.Taking a three-span continuous beam bridge in the near sea as the research object,an extreme wave numerical wave flume model was established to study the extreme wave loads on bridge structures under different wave characteristics and water depths.The results showed that wave height had a significant impact on wave loads.When the wave height was 6m,the peak horizontal wave load on the bridge pier was on average 2.48 times that of when the wave height was 3m.Vertical wave loads were also greatly affected by wave height.The study also showed that the degree of submergence had a significant impact on wave impact loads.When the water surface partially submerged the structure,the wave impact load was stronger,but when the water surface fully submerged the structure,the wave impact force on the structure was significantly weakened.The peak wave load on the main pier composite structure was only 55.56%at a water depth of 29m(7.7m above the pier top)as compared to that at a water depth of 21m(3.3m below the pier top).Based on the study of extreme wave loads,a numerical model of the bridge structure was constructed,and a fluid-structure coupling numerical calculation method was used to study the dynamic response of the near-sea continuous beam bridge under the combined action of extreme waves and local scour.By analyzing the displacement response curve of the components,it was found that when the wave height increased,the component was subjected to a greater wave impact,resulting in an increase in the peak displacement of the structure.The beam was subjected to direct wave impact at a water depth of 24m and 29m,resulting in a significant overall displacement change of the structure.Local scour reduced the bearing capacity of the pile foundation and had a significant impact on the dynamic response of the structure.At scour depths of 3m,6m,9m,and 12m,the peak lateral displacement of the pier top was 1.37 times,1.99 times,2.98 times,and 4.44 times that of the non-eroded state,respectively.Through the analysis of the normal stress and shear stress of the pile foundation,it is revealed that there is a stress extreme at the connection between the pier and the pile foundation and the local scour line on the seabed.The connection between the pier and the pile foundation is subject to a large moment,and the pulling side of the pile foundation is prone to cracking.The increase in the depth of local scour makes the pile foundation more vulnerable to damage.The side-span pile foundation experiences bending cracks at a peak moment with a scour depth of 12m,a wave height of 3m,and a water depth of 21m.On the local scour surface of the seabed,the peak and variation rate of shear stress of the pile foundation increase with the increase of local scour.Also,the pile foundation at this position is subject to negative moment,and the pulling side is prone to cracking damage.Under the action of waves,the bridge bearings are mainly subjected to horizontal and vertical loads.When the wave height reaches 6m,the peak horizontal reaction force of the bearings approaches their ultimate bearing capacity,resulting in damage and failure.When the beam body is directly impacted by waves,under the joint action of horizontal impact force,vertical impact force,and water buoyancy,the beam is prone to overturning.This study has revealed the mechanism of wave load and dynamic response of various components of the nearshore continuous beam bridge under the combined action of extreme waves and local scour,providing a theoretical basis for the study of defense measures for nearshore bridges under the combined action of dual disasters.