Study On Mechanism Of Flood Force And Disaster Reduction Measures Of Superstructure Of Multi-box Girder Bridge

China is one of the countries with the most frequent flood disasters in the world because of its vast territory,complex physical geography and climate conditions.The occurrence of flood will cause a large number of multi-box girder bridge with small and medium-sized span along the way to be destroyed by water.In the past bridge design,the possible flood impact on the superstructure above the design water level has not been considered.On the one hand,there is no relevant provisions in the specification to restrict it.On the other hand,the flood return period used in the design is generally short,resulting in the insufficient flood resistance of the bridge superstructure.At present,there is little research on the flood force of bridge superstructure in China,and there is a relative lack of information.Therefore,it is necessary to carry out in-depth study on the flood force of bridge superstructure,thoroughly understand the force mechanism of bridge superstructure under flood action,and put forward feasible flood control measures for superstructure.The main contents of this paper are as follows:(1)Based on the finite element software,a two-dimensional numerical model is established to simulate the impact of flood on the bridge deck in the case of rising water level in the actual project,and to explore the coupling mechanism of bridge-flood-air.Considering the influence of air entrained in the chamber under the beam,this paper focuses on the analysis of the pressure variation mechanism and the process of air escape in the chamber.At the same time,the mechanism of horizontal and vertical forces on the superstructure of the bridge under the action of flood is deeply studied.(2)By means of model test,the influence factors of bridge-flood-air coupling flow field are further explored.By changing the flow velocity,bridge installation height and submergence depth,the magnitude and variation of flood force of bridge deck model are explored under different flow field conditions.It mainly includes the influence of submergence rate,approach rate and bottom boundary under the condition of fixed blocking rate.(3)Several flood control measures are put forward to reduce the flood force of bridge deck and the possibility of bridge deck being destroyed by flood.It mainly includes the use of hollow railings,the opening of air holes on the top of the chamber to exhaust the air in the chamber,and the installation of fairing on the upstream surface of the bridge deck.