Study On Mechenical Properties Of Cross-sea Bridges Substructure Under The Effects Of Wave And Current

In the wake of human production and life penetrating into oceans, cross-sea bridges are emerging in quantities along with the inevitably requirements for traffic facilities. These bridges are not only required to meet their designed functions, but also to bear various complex and severe ocean loads. The piles and foundations of these cross-sea bridges, in particular, manifest a far more complex stress state than that of inland bridges under the interactions of waves and ocean currents since the completion of construction. Therefore, it is of great significance to conduct a study on mechanical properties of these structures by taking into account of the marine environment loads in form of waves and ocean currents.This study is supported by Hubei Provincial Natural Science Fund(2014CFA122) "Study on Dynamic Response of Cross-sea Bridges Foundations under the Effects of Wave Current Force". The main research details of this thesis are stated as follows:1. The effect of linear wave, Stokes 5th Wave as well as the random wave on a steel-pipe pile foundations is respectively calculated by CFD numerical simulation. Based on linear wave superposition method, a simulation is conducted on the irregular ocean wave spectra by CEL language to compile random ocean wave programs and simulate real ocean environment. The correctness and effectiveness of the numerical wave tank is verified by comparing that of theoretical values and measured data by constructing a numerical wave tank related to measured data, which provides basis for analyzing the force bearing properties of subsequent bridge foundations.2. By calculating wave forces and displacements on top of columns under the working circumstances of various column diameters, comparative water depths, wave heights as well as the wave periods, the thesis summarizes the changing rules of wave force on cylinders with/without regard to fluid-solid coupling effects, and then confirms the sensitive parameters that influence fluid-solid coupling effects by comparisons.3. By summarizing the effects of ocean current on the properties of wave movement, a structural dynamics equation is specified by taking into account of the column vibration to fluid under the combined actions of waves and currents, with the establishment of finite element model under the combined actions of waves and the currents of deep water columns by taking into account of the fluid-solid coupling effects. The question is decouple by discreting the equation on time with the Newmark-? Method, and this program is writen by MATLAB. The effect of current velocity, angle of wave and current on the force of pile, as well as the effect of cross-section shape and size on the value of wave-current force is discussed.4. With the establishment of group piles platform model, the changing rules of single pile and total force interference factor are summarized by studying influence on force bearing status of each pile in accordance with the changes of pile distance and pile location.Under the effect of wave load, the interaction of pile group arranged perpendicular to the moving direction of waves enlarges the wave force of each pile, this effect increases with the growth of pile spacing. The interaction of pile group arranged along the moving direction of waves weakens the wave force of each pile, this effect declines with the growth of pile spacing. Comparatively, when perpendicular to the moving direction of waves, the influence of KC number on interference coefficient of each pile is not obvious, however, along the moving direction of forward waves, the interference coefficient of each pile tends to decline with the increasing number of KC, and such influence is more obvious on back pile.By conducting a systematic study on mechanical properties of cross-sea bridge piers and its pile foundations under the effect of waves and ocean currents, the thesis puts forwards with some suggestions on designing substructures of cross-sea bridges, which is of certain reference value in designing structures of similar types for future.