Aerostatic Stability Analysis Of Long-span Suspension Bridges During Construction Under Skew Wind

With the further increase of span length of suspension bridge,it becomes more flexible and more sensitive to the wind action,especially under construction state.Due to the limited length of erected girder segments and weak connections between the girder segments,structural stiffness is less,and thus the wind stability is more serious.At present,it is generally assumed that wind normal to the bridge axis has been the most critical,however the maximum wind at bridge sites is generally skew to the bridge instead.It is also confirmed by wind tunnel test that wind stability of suspension bridge in completion may be worsen under skew wind.To ensure construction safety of long-span suspension bridge under skew wind,it is necessary to conduct aerostatic stability analysis of long-span suspension bridges during construction under skew wind.Firstly,this paper introduces the current researches on the wind stability of long-span suspension bridge during construction,and the necessity of considering the skew wind action in aerostatic stability analysis of long-span suspension bridge under construction is presented.Under the skew wind action,through accurately considering the nonlinearities of structure and static wind load,the method of three-dimensional nonlinear aerostatic stability analysis of long-span bridges is established,and its computational procedure SNAA-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 states of the bridge in completion and cable finished stage areanalyzed.On this basis,the ideal structural states of each construction stage are analyzed under three deck erection sequences: the girder segments symmetrically erected from the midspan to the two side towers,from the two side towers to the midspan,and four working fronts.Thirdly,the aerostatic stability analysis program are used to analyze the aerostatic stability of long-span suspension bridge in completion,and the effect of skew wind on the aerostatic stability of completed suspension bridge is discussed.Finally,for the suspension bridge under skew wind,the aerostatic stability of the bridge during erection under three deck erection sequences is investigated numerically by SNAA-SW,the evolution of aerostatic stability is revealed,and the effects of skew wind and deck erection sequence on the aerostatic 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 aerostatic stability under skew wind is better,which is considered to be an ideal erection sequence.(2)The effects of wind attack angle and skew angle on the aerostatic stability of suspension bridge are different.The wind attack angle changes the mode of aerostatic instability,and however the wind skew angle can significantly affect the critical wind speed of aerostatic instability.(3)The minimum critical wind speeds of aerostatic instability of suspension bridge under construction and completion stage often occur under the skew wind,which may bring about an average reduction of 3.8% and 5.4% as compared to normal wind.Therefore,the effect of skew wind must be considered in aerostatic stability analysis of long-span suspension bridge under the construction.