Research Of Wave Motion And Its Effect On The Bridge Substructure In Coastal Area

The effect of water waves on sea-crossing bridge,including wave force and scour on the pier or pile foundation,seriously threatens the safety of bridge,which has attracted widespread attention from scholars in the world.Both hurricane and seafloor movement can generate rogue waves,which would produce destruction to the structures in near-shore area.Nowadays there are still some shortcomings in the research of the influence of wave current on bridge safety.For example,the interaction between seafloor movement and water waves has not been studied comprehensively,and the characteristics of wave generated by seabed movement are still not clear.Moreover,the transformation,breaking as well as hydrodynamic characteristics are very complex when the wave propagates in near-shore area.There are fewer studies on the interaction between water waves and complex bridge substructure.This paper focused on the subject of wave action on the bridge.Based on the fundamental equations of fluid mechanics and sediment transport theories,the research was conducted by numerical and experimental methods.The mechanism of water waves generated by seafloor movement and wave propagation in near-shore area were analyzed.The wave forces and scour subjected by different types of bridge substructures were studied.Finally,the impact of scour and wave force on the structure in near-shore area was discussed.The main research results are as follows:(1)Based on the fundamental equations of fluid mechanics and sinusoidal assumption of seafloor movement,the influence of seabed movement parameters on wave characteristics was studied.The conditions for the occurrence time of maximum wave elevation were obtained,including the frequency of seafloor movement and the ratio of wave amplitude and water depth.Compared with linear model,the results indicate that the nonlinearity can be neglected when the periodic function of seafloor movement is less than 1 and the ratio of wave amplitude and water depth is larger than 0.025.The proportions of various terms under linear and nonlinear conditions were obtained.(2)The Reynolds-averaged Navier-Stokes equations were incorporated into standard k-? turbulence model and applied to simulate wave breaking under the influences of different beach slopes.Considering the viscidity and fluctuation of fluid,a breaking criteria was proposed,which is applicable for lager range of beach slope.The effects of beach slope on the hydrodynamic characteristics under the conditions of wave non-breaking and breaking were obtained.(3)The influences of incident wave height and structure type on wave forces were studied.Under the specific conditions of this paper,the increase of total force on pile foundation with pile spacing and incident wave direction was small.The total force on pile foundation increased Avith KC number and relative wave height according to the rule of power exponent.It is due to that the current-obstruction width of the composite structure varies greatly in vertical direction,the effect of relative wave height on the wave force subjected by the bridge substructure is more significant compared with KC number.(4)By the experiment and data analysis,it was obtained that the scour on the bed surface with steep slope was the major component of total scour around the pier.The proportion was related with the height of the bed slope.Based on the physical process of wave scour in near-shore area and the real-time change of wave force,the structural dynamic analysis was carried out.The results indicate that the natural frequency decreased with increasing scour depth.The displacement of pile-head varied greatly with scour depth and wave force.Under the conditions of this paper,the largest increase of displacement of pile-head was twice as large as that with no scour.