Study Of Extreme Wave Action On The Superstructure Of Coastal Box Girder Bridges

With the steady advancement of the “Marine Power” and “Belt and Road”national strategies,the rapid development of the economy in coastal areas has put forward a continuous need for cross-sea transportation.The construction of near-sea bridges in China has achieved great success.Coastal bridges are an important part of the transportation network in coastal areas and a “throat” link in the regional transportation network.However,coastal bridges located in the marine environment may encounter extreme waves caused by typhoons or tsunamis,which may cause the bridge girder to shift and lead to the interruption of regional transportation,resulting in huge economic and social losses.Therefore,research on the wave force characteristics and influencing factors of coastal bridge girders for extreme waves acting on bridge structures has important theoretical and engineering significance for ensuring the safety of coastal bridge structures.This thesis takes the box girder structure commonly used in the construction of coastal bridges as the research object.Through numerical simulation and theoretical analysis,it studies the wave force acting on the upper structure of the box girder under wave action.The main research contents are as follows:(1)A three-dimensional numerical simulation of dam-break waves in a wave flume was established based on the open-source computational fluid dynamics software OpenFOAM.The numerical model that can accurately simulate the wave action of box girder dam break was established by verifying the numerical model with the classical dam-break wave theory model and the experimental results of Japan’s PWRI laboratory.(2)Based on the established numerical model,the parameter analysis of the wave action of box girder with and without superelevation was carried out.The action process of tsunami wave on the upper structure of box girder bridge was divided into impact stage and flow-around stage.For the box girder without superelevation,the influence of upstream water storage depth,downstream still water depth and clearance height under girder on tsunami force in impact stage was analyzed.For the box girder with superelevation,the influence of superelevation angle and upstream water storage depth on tsunami force in impact stage and flow-around stage were analyzed respectively.(3)A theoretical calculation model of wave force on the upper structure of a fully submerged box girder on a non-flat seabed was established based on the potential flow theory.The boundary value problem of the seabed-wave-box girder system was defined based on necessary assumptions and simplified definitions.The velocity potential of the flow field was obtained by using the potential flow theory and the eigenfunction matching method,and the wave force on the upper structure of the box girder was calculated using Bernoulli’s principle.Finally,the correctness of the theoretical calculation model proposed in this study was verified by experimental results.(4)Based on the theoretical calculation model of wave force on the upper structure of the box girder established,the wave force characteristics of the upper structure of the box girder under submergence state were studied.Furthermore,the wave load parameters of the upper structure of the box girder behind a trench or breakwater were analyzed,and the influence of geometric characteristics of trench,breakwater and box girder on wave load was discussed.Finally,recommended geometric setting parameters were given.