Refined Analysis And Research On Flutter Stability Of Long-span Suspension Bridges Under Construction

Suspension bridge is the main bridge structure system among the bridges whose main span are more than 1000m.The stiffness and damping of the suspension bridge are small,so it is very sensitive to the wind action,especially the transient structure under construction.Because the bridge has not yet formed the final structural system,structural rigidity especially torsion stiffness is much smaller than that in the completion,the bridge is more unstable,the great deformation of the bridge under the wind action,the declination of structural stiffness and wind speed spatial non-uniform distribution may have prominent effect on the wind stability.Therefore in this paper,taking a long-span suspension bridge under construction as example,its dynamic characteristics and flutter stability under the whole construction process are analyzed,the evolutions are revealed,and the effects of structural nonlinearity,the static wind action,the width of wind speed distribution and the asymmetric distribution of wind speed on the flutter stability of long-span suspension bridges under construction and completion are investigated,which provides a theoretical reference to ensure safe construction of long-span suspension bridges.Firstly,using the finite element analysis software Midas/Civil,a three-dimensional finite element model of Runyang bridge is established,then the ideal states of the bridge in completion and free cable status are analyzed.On this basis,the construction ideal states of two deck erection sequences,which are the deck erected symmetrically from the midspan to the two side towers and from the two side towers to the midspan,are analyzed.Secondly,using the dynamic characteristics finite element program SDCA,structural dynamic characteristics of the bridge during the whole construction process for two deck erection sequences are analyzed,the evolution and influence of deck erection sequence on dynamic characteristics are revealed.Lastly,using three dimensional nonlinear flutter analysis program of long-span bridges in which structural nonlinearity,static wind effect and wind speed spatial distribution are all considered accurately,the evolution of flutter performance in the whole construction process of two deck construction sequence is investigated,and the reasonable and feasible deck erection sequence is explored,and the influence of structural nonlinearity,static wind effect and non-uniform distribution of wind speed on flutter stability of long-span suspension bridge under construction is discussed.The results show that:(1)the change of structural state is more smooth,and higher stiffness and better flutter stability is achieved as the deck is erected from the two side towers to midspan,especially in the early stages,which is considered to be an ideal erection sequence;(2)the great deformation and structural stiffness variation under the static wind action has significant influence on the flutter stability of long span suspension bridge under construction,and it must be accurately considered in the analysis;(3)the wind speed spatial distribution width has little effect on the flutter critical wind velocity of the bridge under construction,but the spatial asymmetric distribution of wind speed has remarkable influence,therefore it is necessary to consider the wind speed spatial non-uniform distribution in flutter analysis.