Dynamic Response Of Discrete Pontoon Offshore Floating Bridge Under Combined Action Of Moving Vehicles And Wave Load

In this paper,aiming at the new cross sea traffic facility of discrete pontoon offshore floating bridge,the interaction between pontoon and wave is simulated by computational fluid dynamics(CFD),the superstructure and vehicle load of floating bridge are simulated by finite element method,and the connection between them is established by co-simulation to study their response under the combined action of moving vehicle and wave load.In ABAQUS,the spring and damping element is used to establish the three-dimensional vehicle model,and the vehicle axle interaction is realized through the deformation coordination condition,In Star-CCM+,the first-order wave of VOF is used to simulate the wave action.The structural solver ABAQUS and the fluid solver Star-CCM+exchange pressure and node displacement between each time step to realize fluid structure interaction.The numerical simulation methods used in this paper are verified from three aspects:wave action,vehicle action and fluid structure interaction.Taking a steel truss bridge as an example,a wave-vehicle-floating bridge interaction system is established.Under the action of wave loads in different periods,the displacement of each pontoon increases gradually from both ends to the middle;The vertical displacement of the floating bridge increases monotonously,while the transverse displacement first increases and then decreases;The transverse response of the floating bridge is much more sensitive to the change of wave period than the vertical response,and the transverse response is much greater than the vertical response.For the discrete pontoon offshore floating bridge without mooring device,the transverse wave load plays a controlling role in its response.In the design of the floating bridge structure,it should be avoided that its first-order transverse bending frequency is close to the wave period.The mooring device will not reduce the response of the floating bridge under all wave periods,which should be set according to the significant wave periods in the actual project.According to the combined action of wave and vehicle,the dynamic amplification factor of floating bridge is introduced,which increases with the increase of vehicle mass and first increases and then decreases with the increase of vehicle speed.The theoretical peak bending moment of each span of floating bridge at different speeds is further given for design reference.In view of the important influence of transverse wave load,this paper also selects the concrete box girder bridge with the same span and similar bridge width as the steel truss floating bridge,but with greater transverse stiffness as the superstructure of the floating bridge.Compared with steel truss floating bridge,the vertical displacement and bearing internal force of concrete floating bridge are reduced slightly;Although the lateral displacement decreases significantly,the internal force at the support also increases significantly.In practical engineering,we should pay attention to the design of the support.This paper also simulates a simple traffic flow through the concrete floating bridge.The results show that the mid span bending moment of the middle three spans is reduced compared with the working condition of two vehicles passing side by side,while the mid span bending moment of the side span is significantly increased,which further shows that more attention should be paid to the structural design of the side span for the concrete floating bridge.