Study On Wave Forces Acting On Superstructures Of Coastal Bridges

The coastal bridges are an important part of the highway transportation network in the coastal zones.The built coastal bridges without enough clearence would be severely damaged by the typhoon-or hurricane-generated waves.The absence of the coastal bridges would hindered rescue and reconstruction efforts in the affected area and led to serious economic and social losses.The catastrophic failure of caused by the waves,and due to transport disruptions.The hurricane wave is a considerable risk to the low spans of coastal bridges because the coastal bridge are not specially designed to defend the wave loads.There is great significance to investigate the process of the wave acting on the bridge superstructure,to find out the corresponding key factors and to explore reasonable estimation method of the wave forces.This thesis investigated the wave action on the bridge superstructure and analyzed the influencing factors.The main contents,methodologies and conclusions are:(1)A 1:10 scaled hydrodynamic experiment was conducted in the wave flume.The specimen consisted a full length of bridge span,two neighboring segments and substructure.The prototype of superstructure spans was selected from the Standard Drawings of Highway Bridge of China.A series of hydrodynamic tests were carried out to investigate the wave forces acting on the bridge model and the pressure on the bottom of superstructure under various wave conditions,clearances and wave directions.The characteristics of the wave forces were analyzed based on the experimental data.It was found that the vertical force contained a high frequency component and a low frequency component with a comparable amplitude while the horizontal wave force does not have a obvious high frequency component.The forces acting on the superstructure showed different relationship with the wave elements under different wave directions and clearances.The experimental results showed that the superstructure experienced the maximum forces when the wave incident perpendicularly for zero clearance and submerged cases while the wave incident at 15 dgeree for elevated case.The bearings on the offshore side experience more wave loads than those on the onshore side.(2)A 2-dimenisonal model were set up based on the potential flow theory to investigate the wave action on the submerged bridge decks under normal waves.The governing equations were solved under the simplified boundary conditions,and the velocity of the whole fluid domain ware obtained by the eigenfunction expansion matching method.The theoretical models were validated by the results of two different wave flume experiments.The comparison between the theoretical results and the AASHTO guideline showed the AASHTO guideline overestimated the vertical wave force while underestimated the horizontal wave force.A simple method was developed based on the results from analytical solution can be used for the estimating of the maximum wave forces on such structures mentioned by the AASHTO guideline during the design process.(3)The wave forces acting on the submerged superstructure under the oblique waves were studied by the 3-dimenisonal analytical model setup basing on the potential flow theory.Firstly,the govering equations of this boundary value problem was simplofied into the Helmholtz equation from 3-dimensional Laplace equation under some necessary assumptions.Then,the mathematical formula and analytical solution of this wave-structure interaction problem were derived using the method of separation of variables.The wave forces acting on the submerged deck under oblique waves were obtained from the velocity field by applying Bernoulli theorem after the unknown coefficients in the velocity potentials are determined.The analytical solution of the wave force was validated by two hydrodynamic experiment results.Using the proposed method,the influence of the wave direction and the geometry of the bridge deck were examined.It was found that the submerged bridge deck experienced the maximum wave forces when the incident wave was perpendicular to the bridge span.The geometry of the structure members had limited influence on the wave forces.(4)A hydrodynamic experiment was conducted to study the wave impact on the structure under multi-focused waves and an analytic model basing on the potential flow theory was set up.The multi-focused wave was generated in the wave flume by the wave-wave interaction method to simulate the real rogue waves.The observed wave elevation was compared with the theoretical target to validate the wave maker can generate the required waves in the narrow wave flume.The bridge superstructure was simplified into a rectangle box in this experiment.The impact pressure on the bottom of the box was measured under various focused wave.The wave condition covered different peak frequency,maximum wave amplitude and clearances.The test results showed that the pressure distribution on the bottom of the box was influenced by the peak frequency and the maximum amplitude of the focused significantly.The results of the analytic model were valicated by the test results.The calculated results showed that with the increase of the peak frequency the horizontal wave force increased firstly and decreased subsequently,the vertical force declined sustainedly.The horizontal and vertical forces all increased near linearly with the growing of the maximum amplitude of the input focesed waves.