Refined Analysis Of Flutter Stability For Long-Span Suspension Bridges During Construction Under Skew Wind

With the development of suspension bridges to super long-span,they are becoming more flexible and sensitive to the wind action,especially under construction.During deck erection,the length of erected girder is short and there is no effective constraint between the girder segments,structural stiffness is less,and the wind stability becomes more serious.The field measurements and studies show that bridges are mainly subjected to the skew wind action,and the wind stability of suspension bridges in completion is the worst under the skew wind.In order to accurately evaluate the flutter performance of long-span suspension bridges during construction,it is necessary to conduct refined analysis of flutter stability for long-span suspension bridges during construction under skew wind.Firstly,this paper introduces the current researches on the wind stability of long-span suspension bridges during construction,and the necessity of considering the skew wind action in flutter stability analysis of long-span suspension bridges under construction is presented.Under the skew wind action,through considering the static wind effect,a three-dimensional nonlinear flutter stability analysis method is established,and its computational procedure nflutter-sw is programmed.Secondly,taking the Runyang Suspension Bridge as example,a three-dimensional finite element model of the bridge is established by using the finite element software Midas/Civil,structural status of the bridge in completion and free cables are analyzed.On this basis,the ideal structural states of each construction stage are analyzed under three deck erection sequences: the girder segments symmetrically assembled from the midspan to the two side towers,from the two side towers to the midspan,and four working fronts.On the computed structural equilibrium states of each construction stage,structural dynamic characteristics is analyzed by using the computer program SDCA,the evolutions of dynamic characteristics of the bridge under three deck erection sequences are revealed.Thirdly,the linear and nonlinear flutter stability analysis program are used to analyze the flutter stability of long-span suspension bridge in completion,and the effects of static wind action and skew wind on the flutter stability of completed suspension bridge are discussed.Finally,for the suspension bridge under construction,the linear and nonlinear flutter stability analysis are conducted to investigate the evolution of flutter stability under skew wind of the bridge during construction under three deck erection sequences,and the reasonable and feasible deck erection sequence is explored,and the effects of static wind action and skew wind on the flutter stability of suspension bridge under construction are discussed.The research results show that:(1)as the deck is symmetrically erected from the two side towers toward the midspan for long-span suspension bridge,the geometry and inner force change more smoothly during construction,and the flutter stability under skew wind is better,which is considered to be an ideal erection sequence.(2)The static wind effect has a significant impact on the flutter stability of long-span suspension bridge under construction,which may bring about an average reduction of 3.7%-7.5%.therefore,it is necessary to consider accurately the static wind effect when analyzing the flutter stability of long-span suspension bridge under construction.(3)The minimum flutter critical wind speeds of suspension bridge under construction and completion stage often occur under the skew wind,which may bring about an average reduction of 5.4% as compared to normal wind.Therefore,the effect of skew wind must be considered in flutter stability analysis of long-span suspension bridge under the construction.