Study On Dynamic Response Of A Long-span Floating Bridge Suspended From Tension Leg Foundation Under Wave And Wind Loads

China had built many long-span sea-crossing bridge which adpoted fixed foundations.However,when the water depth at the site is very deep and the soil of seabed is soft,it is impratical to bulid sea-crossing bridge using the traditional fixed foundation.To solve the above problems and satisfy navigable requirements,foreign researchers proposed a design concept of long-span floating bridge suspensed from tension leg foundation.In the process of design and analysis of long-span floating suspension bridge,the combination of wind and wave loads should be focused on.However,there is still few studies about the dynamic response of long-span floating suspension bridge under wind and wave loads,it is urgent to conduct more detailed researches.On the basis of the design scheme of long-span floating bridge suspensed from tension leg foundation,this thesis carried out detailed analysis about dynamic response under wind and wave loads by means of approaches including numerical simulation and theoretical derivation.The main research contents include:(1)This thesis summarized three design schemes of long-span floating bridge suspensed from tension leg foundation which are used to cross Bj(?)rnafjorden fjord,and compared the design pramaters and the modal analysis results.It was found that different foundation types can significantly change the natural period of the modes related to the motion of foundation and the vertical modes of girder.(2)This thesis verified the validity of the simulation method of random wind load and random wave load.Then based on the simulation method this thesis developed dynamic analysis method of floating bridge integrating AQWA–USFOS software.The reasonability of the definition method of added mass and added damping was discussed according to time domain analysis and power spectrum analysis.According to the analysis,the dynamic response of the tension leg foundation is mainly dominated by the first order mode and the second order mode.Within the corresponding period,the motion response of the structure is less affected by the change of the added mass and the added damping.The added mass and the added damping corresponding to the first order period can be used for the analysis of the floating structure.(3)This thesis studied the influence of the spatial coherence of wind load,the second order wave load and direction distribution parameters on the dynamic response of long-span floating bridge suspensed from tension leg foundation.The motion and internal force response results of main girder were obtained by the time-domain analysis,meanwhile,the influenc mechanisms of the modes were explained according to the results of spectrum analysis.The reults showed considering the spatial coherence of wind load will make the structural response becomes smaller,the second order wave load can significantly increase the lateral motion response of the structure,and the choice of direction distribution parameters has a great influence on the motion response.(4)This thesis studied the influence of the draft depth of the tension leg foundation,the angle of tethers and the height of the bridge pylon on the dynamic response of long-span floating bridge suspensed from tension leg foundation.The motion and internal force response results of main girder were obtained by the time-domain analysis,it is found that reasonable design parameters can effectively reduce the response of long-span floating suspension bridge under wind wave loads.