Wind,Wave And Current Joint Actions And Dynamic Responses Of Long Span Sea-Crossing Cable-Stayed Bridges

In recent years,the constructions of sea-crossing bridges in China are developing rapidly and have achieved great accomplishments.The sea-crossing bridges,especially the long span types,need to resist on the severe meteorological and hydrological conditions,such as the deep water,rapid currents,huge waves,and strong winds,which could introduce serious threat to the safety of structure.The foundations of sea-crossing bridges are usually affected by wave and current loads,while the superstructures of bridge are mainly affected by wind loads.Under the combinations of wind,wave and current,the large displacements and violent vibrations of sea-crossing bridge may be induced during the construction and operation periods,which will affect the construction progress and endanger the safety of structure.The mechanism of action of wind,wave and current on the long span sea-crossing bridge,and the vibration response characteristics still remain to be explored and resolved.The corresponding experimental and numerical simulation techniques on this subject also need to be developed urgently.Based on the existing bridge design specifications,the considerations of wave and current loads on the bridges are insufficient,which may overestimate or underestimate the environmental design loads.Therefore,the wind,wave and current joint actions and dynamic responses of long span sea-crossing cable-stayed bridges are concerned in this dissertation,and the main research contents are as follows:(1)In order to investigate the mechanism of wave and current joint actions on the bridge towers of long span sea-crossing cable-stayed bridges,the three representative bridge towers with different structural styles are chosen as the research subjects,and the experimental studies are conducted based on the elastic model test similarity criterion.A simplified dynamic structural similarity model test design method is proposed using a "composite material".The loading features and motion responses characteristics of bridge towers subjected to wave,current and wave-current actions are obtained based on the analysis of experimental results.The flow resistance coefficient of different bridge tower foundation structure are confirmed,which could be referenced for the load effects calculations and structural designs of sea-crossing bridges.(2)The simplified calculation methods of wave force on the large round-ended caisson foundations and gravity pier foundations are investigated aiming to convenience engineering application.Based on the theoretical calculation method of wave forces on large circular cylinder and the empirical calculation formula of wave forces on large rectangular cylinder,a simplified calculation model of wave forces on a large round-ended caisson foundation is established,and the inertia coefficients is determined through the boundary element numerical simulation method.The feasibility of established new method is also validated by the experimental results.On the other hand,the wave force features on the gravity pier foundation are also analyzed through the hydrodynamic model test and boundary element numerical simulation method.The simplified calculation method of wave forces and the inertia coefficients on the gravity pier foundation is proposed,which are convenient for engineering application.(3)In order to investigate the dynamic responses characteristics of bridge towers subjected to wind,wave and current joint actions,a free-standing diamond-type bridge tower is taken as the research object.Firstly,the wind-drag coefficients of bridge tower under mean wind action are numerical simulated and compared with the experimental results.The compared results show roughly consistent,which means that the wind-drag coefficients are reasonable.Then,the wind,wave and current forces on the bridge tower are compared and analyzed.The features of horizontal forces and moments on the bridge tower subjected to wind,wave and current are obtained.Finally,the dynamic responses of bridge tower subjected to wind,random wave and wind-wave actions are numerically calculated,and the dynamic response characteristics of bridge tower subjected to wind and wind-wave actions are obtained,which could be taken as references for engineering designs.(4)Based on the diamond-type bridge tower above,a long span sea-crossing cable-stayed bridge is concept designed,and the load effects of wind,wave and current on the bridge are investigated.The check analysis is conducted,and the wind,wave and current action forces characteristics and induced dynamic responses of bridge are calculated and analyzed.The research results could be used as references for the design of long span sea-crossing bridge.(5)In order to analyze the wave effects on the caisson foundations of long span sea-crossing bridges,the base pressures of caisson foundations subjected to dead loads,wind,and wave loads are investigated.It is revealed that the wave effects on caisson foundations can not be ignored.Based on this,the wave effects on caisson foundations with different section shapes are investigated.The comparison results could be taken as references for the structure design selection of caisson foundations.