Response Characteristics And Train Running Performance Of Long-span Bridge Under Correlated Wind And Waves

With the promotion of Chinese "One Belt and One Road" initiative and the "Ocean Power" strategy,the marine bridge construction is at a peak.Different from land bridges,marine bridges are always simultaneously subjected to strong wind and huge waves.As marine bridges continue to extend to the deep sea,the span of the girder becomes longer,and the depth of the pile foundation becomes deeper,which leads to the decrease of the bridge stiffness.Extreme wind and wave environment bring great challenges to the design,construction and operation of bridges as well as running train.In order to establish an efficient and accurate evaluation method for the dynamic performance of marine bridges and trains under the corrleted wind and waves,the following research is carried out:Based on the field measured data in the bridge site region,the distribution characteristics of the mean wind speed,significant wave height and wave period are analyzed.By comparing the correlation of wind and waves between the codes and the measurement,the limitations of the codes are pointed out.The marginal distribution functions of three wind and wave parameters are estimated by the maximum likelihood method.Finally,based on the Copula model and the Akaike information criterion,the long-term and short-term optimal wind-wave joint distribution models are established respectively,and the most likely wind and wave combination under different return periods is inferred.According to the wind field simulation of the bridge site,the differences of the mean wind speed,the wind spectrum and the coherence function of the ocean and land wind field are clarified,and the calculation method of the wind field and wind load of the marine bridge is clarified.For the wave field in the bridge site region,the differences in the calculation principles of the wave forces between the Chinese,British,and US codes were compared,and the calculation method of the wave field and wave load of the marine bridge is clarified.Aiming at the problem of load combination,based on the Joint Committee on structural safety(JCSS)combination model,three kinds of load combination modes are proposed.The influence of each combination and its combination parameters are discussed,and a wind-wave-current load combination method suitable for the preliminary design stage of marine bridge is proposed.Considering the disadvantages of time-consuming and low accuracy of structural dynamic calculation under the correlated wind and waves,a fast time-domain calculation method for the response of bridge tower under the combined action of wind and waves is proposed.The rationality of the method is verified by comparing the numerical calculation results with the test results in a wind tunnel and wave flume,and the calculation efficiency of the method is improved by introducing the response surface method.The direction effect of the wind and wave load is studied,and the influence of different wind and wave directions on the structural response is clarified.In order to further improve the calculation efficiency and study the influence mechanism of wind and waves on the structure,a frequency domain calculation method of bridge tower response under the correlated wind and waves is proposed by improving the harmonic response analysis.Finally,the seasonal effect,directional effect and water depth effect of wind and wave loads are analyzed.The contribution law of load energy and the response mechanism of the bridge under the single wind,single wave and correlated wind-wave are clarified,and the influence mechanism of different seasons,directions and water depths on the bridge are also interpreted.The wind-wave-bridge coupling dynamic system is established,which contains wind-wave coupling,wind-bridge coupling and pier-water coupling.In this system,the dynamic response of the bridge is solved by Newmark-β method,and then the response characteristics of the long-span bridge under the stationary and non-stationary wind and waves are analyzed.In order to further improve the calculation efficiency,three machine learning methods,i.e.,BP neural network model,support vector regression model and Gauss process regression model are introduced to train and predict the responses of bridge girders,piers and towers.By comparing the prediction accuracy of the three models,the optimal prediction model for bridges is proposed.The effects of mean wind speed,siginificant wave height and spectral peak period on bridge response are discussed.The wave-bridge-train coupling dynamic system is established.The vehicle-bridge response is solved by separate iteration.The effects of wave return period,vehicle speed,water depth and pier stiffness on the train and bridge are studied.The wind-wave-bridge-train coupling dynamic system is established.The influence of wave height,wind speed and vehicle speed on the train and bridge is analyzed.The safety and comfort of the train and the safety of the bridge under the corrlerated wind and waves are evaluated.