Research On The First Passage Reliability Of Long-span Bridges Under Dense Traffic Flow

In recent years,with the rapid development of the global economy and the continuous progress of construction technology,bridge construction also has rapid development.On the one hand,with the rapid development of China's economic construction,road and bridge loads increase at the same time.On the other hand,the safety of large bridges in the operation period is directly related to the national economic development and the safety of humans,life and property.Therefore,the safety of the bridge is becoming more and more prominent.Based on the actual case of Nanxi Yangtze River Bridge in Sichuan Province,the first passage reliability of the bridge is analyzed and the bridge safety in 100 years is predicted,which provides a strong support for the safety of the bridge in practical engineering.The main contents of this paper are as follows:(1)Based on the dynamic weighing system(WIM)of high-way bridges,the probability characteristics of the vehicle speed,vehicle distance and vehicle weight of the random flow of the bridge are analyzed,and the random flow model of the bridge is established.(2)ANSYS finite element model of ANSYS finite element program is used to build the ANSYS finite element model of Nanxi Yangtze River Bridge,simplifying the interaction load between vehicle and bridge,which gives full play to the simplified simulation ability of vehicle and bridge analysis of the post-processing function.(3)It is assumed that the displacement response of the bridge under the action of random flow is Gaussian stable stochastic process,that is,the corresponding structure of the random flow sample has the same history.On this basis,the variables such as the root mean square of the displacement and the root mean square of the velocity for calculating the first super reliability are calculated.Finally,the first passage reliability of the long-span bridge is calculated,and the reliability of the bridge in 100 years is predicted,which has certain engineering significance.The main conclusions are:(1)The dense traffic flow is simulated according to traffic parameters.The influence of bridge coupling on long-span bridges is analyzed by simplified analysis.The vehicle load of dense traffic flow is simplified as the concentrated force,and it is loaded on the Nanxi Yangtze River bridge finite element model.The dynamic response of the bridge is obtained.It can be seen that the response at the L/4 is more severe than the response at L/2.(2)By calculating the first passage reliability of the response of the stiffening girder,it can be seen that the displacement of the stiffening girder of the suspension bridge occurs mainly at the L/4 position.And the suspension bridge girder displacement failure event is mainly caused by the existence of dense traffic flow.In the 100 years,the first passage reliability of the bridge decreases gradually,and the first passage reliability after 100 years is slightly beyond the reasonable reliability range.