Study On Wind-induced Vibration Of A Three-tower Four-span Suspension Bridge With Steel Truss Griders During Erection

Due to the long construction period of long-span suspension bridges,it is impossible to avoid the severe wind conditions during erection.Especially,the overall stiffness of the structure is small,and the bridge is sensitive to wind effects,which makes the aerodynamic stability a great concern.Compared with two-tower suspension bridges,multi-span suspension bridges have greater spanning capacity,but the vibration of each span would affect each other,making the wind response of the bridge structure more complex.In order to improve the aerodynamic stability of multi-span suspension bridges during erection,it is necessary to master the dynamic behavior of each span and put forward targeted countermeasures.Taking the Wenzhou Oujiang Beikou Bridge as the research object in this thesis,the main research contents and conclusions are as follows:Firstly,the dynamic characteristics of the bridge structure is concerned.Using the finite element analysis software,the dynamic characteristics of the three-tower four-span suspension bridge with steel truss griders during erection are investigated.The evolution of the dynamic characteristics with the hoisting rate is analyzed in terms of the vibration participation of each structural member,and the critical flutter wind speed of the bridge in each phase of construction is estimated based on the theoretical equations.Secondly,the influence of the construction sequence of stiffening griders on the structural dynamic characteristics and critical flutter wind speed is concerned,and different structural countermeasures are further considered,including the stiffness of temporary connections,different types of central buckles,rigid suspenders,storm ropes and cross cables.The results show that,the continuous hoisting of stiffening griders of side span from pier to tower can improve the frequencies of symmetric vertical bending and symmetric torsion modes,compared with hoisting from mid-span to pier and tower.The continuous hoisting of the stiffening griders from the bridge tower to mid-span and pier can improve the equivalent mass and equivalent mass moment of inertia in the early stage of construction.The temporary rigid connections between beam segments can significantly improve the frequencies of anti-symmetric vertical bending and anti-symmetric torsion modes,but the improvement of symmetric vertical bending and symmetric torsion modes is relatively limited.The critical flutter wind speed corresponding to the anti-symmetric combination can be increased by strengthening the stiffness of the temporary connection,and the critical flutter wind speed corresponding to the symmetric combination can be increased by restraining the vibration of the end of stiffening griders.Thirdly,the nonlinear aerostatic stability during erection is studied by the combination of increment and double iterations,and the influence of construction sequence on aerostatic stability and the influence of different angles of attack on dynamic characteristics and flutter performance are discussed.The results show that,the continuous hoisting of side span reduces the displacement of side span,but the improvement of aerostatic stability is relatively limited.The construction of stiffening girders from tower to the mid-span and pier can greatly improve the critical wind speed of aerostatic instability in the early stage of construction and reduce the aerostatic displacement of stiffening griders of main spans.The aerostatic nonlinearity considering the initial angle of attack has little influence on the dynamic characteristics and flutter performance of anti-symmetric combination.However,for the symmetric combination,the influence of aerostatic nonlinearity on flutter performance is much different at different angles of attack.Finally,the weighted least square method is used to identify the flutter derivative,and then the multi-modal SRSS analysis method is used to analyze the buffeting of the construction stage of 8.5%.The results show that,the buffeting response obtained without considering the aerodynamic admittance is larger.For the blunt cross-sections,the aerodynamic admittance function can be taken as 1.0.The buffeting response during erection is large,and the influence of turbulence on the bridge of construction stage should not be ignored.