A Study On Random Vibration Explicit Time-domain Method For Seismic Analysis And Wind-resistent Analysis Of Long-span Bridges

With the rapid development of the economy and society in China,the construction of long-span bridges is in the ascendant.Natural disasters such as earthquake and wind would have a significant impact on the safety and reliability of bridge structures directly.In general,long-span bridges take the part of important transportation hubs.Therefore,seismic design and wind-resistant design have become indispensable parts of structural design for long-span bridges.In the traditional analysis methods of structural design,seismic and wind excitations are usually regarded as equivalent static loads or deterministic dynamic loads.However,seismic and wind excitations have intrinsic uncertainties due to the fact that they are affected by various complex factors.It would be more realistic to treat them as random processes,and it is more reasonable to carry out seismic and wind-resistant analyses of long-span bridges using random vibration methods.For traditional random vibration anaylsis methods,they are difficult to be extended to realistic engineering application for non-stationary random vibration analysis of long-span bridges due to the restrictions of non-stationarity of random excitations,structural nonlinearity and computational scale.Therefore,it is of great theoretical and practical significance to conduct the research on highly efficient random vibration methods for seismic and wind-resistant analyses of long-span bridgesIn this dissertation,a systematic study is carried out for seismic random analysis,energy-dissipation random analysis and buffeting random analysis of long-span bridges,which is devoted to putting forward a class of efficient and practical random vibration analysis method for long-span bridges under random seismic excitations or random buffeting excitationsThe primary work of this dissertation is described as follows(1)The existing analysis methods of random vibration are systematically introduced.In other words,a systematic summary is made on current researches on linear and nonlinear random vibration methods.Then a review is made of the progress in dynamic reliability analysis and stochastic optimal design of structures.The recent developments for seismic and wind-resistant analysis methods of long-span bridges are also elaborated(2)In order to break through the bottleneck of practical application of random vibration methods to seismic design of bridges,an efficient and practical method for random vibration analysis is in urgent demand for bridge engineers.Based on the random vibration explicit time-domain method(ETDM),an efficient random vibration approach developed in recent years,and the current seismic design code of highway bridges,a time-domain explicit random simulation method is developed for seismic analysis of bridges.The seismic analysis of the Humen 2nd Bridge crossing the Nizhou waterway with a main span of 1688m is taken as an engineering example for illustration of the efficiency and practicality of the present method.The existing issues of the response spectrum method are also revealed when it is used for the seismic design of long-span bridges.(3)In the light of the locally nonlinear behavior of energy-dissipation structures with viscous dampers,only those local degrees of freedom related to viscous dampers are required for dimension-reduced solution with the advantage of dimension-reduced representation of the time-domain explicit expressions for dynamic responses and their sensitivities.An explicit time-domain dimension-reduced iteration method is proposed for fast nonlinear time-history analysis of structural responses and their sensitivities with respect to the parameters of viscous dampers.The above dimension-reduced analysis method is taken to be the sample analysis method for random simulation of structural responses and their sensitivities,and an efficient Monte-Carlo simulation(MCS)method is further proposed.The present method can be termed as MCS based on explicit time-domain dimension-reduced iteration scheme,which can serve as a high-efficiency random vibration method for nonlinear random vibration analysis and stochastic optimal design of large-scale complex energy-dissipation structures with viscous dampers.Based on the explicit time-domain dimension-reduced iteration scheme,the subset simulation technology is used to reduce the number of samples required in the MCS,namely,subset simulation based on explicit time-domain dimension-reduced iteration scheme,further improving the computational efficiency of dynamic reliability analysis of energy-dissipation structures.To illustrate the accuracy and efficiency of the proposed method,the stochastic optimal design of viscous dampers for the Humen 2nd Bridge crossing the Nizhou waterway with a main span of 1688 m is conducted at first.After that,the stochastic response analysis and dynamic reliability analysis of the bridge are also carried out with the optimal parameters of viscous dampers.(4)Based on the time-domain explicit expressions of buffeting responses and their sensitivities,an efficient random vibration analysis approach is developed for buffeting response analysis and vibration reduction problems of long-span bridges.The developed method can serve as a high-efficiency random vibration approach for buffeting random analysis of long-span bridges.For long-span bridges exposed to non-stationary turbulent wind velocity excitations,a systematic study on stochastic optimal design method for tuned mass damper(TMD)devices and buffeting reliability analysis method is further carried out based on the time-domain explicit random simulation method.The buffeting random analysis of the Egongyan Bridge with a main span of 600 m,including buffeting response analysis,stochastic optimal design of TMD devices and buffeting reliability analysis,is taken to be an engineering application example for illustration of the efficiency and practicality of the time-domain explicit random simulation method(5)Based on the above researches,a software involving the time-domain explicit random simulation method for seismic and wind-resistant analyses of long-span bridges is developed The software development platform,software architecture,software modules and their functional characteristics are emphatically elaborated.The developed software provides an effective computing platform for non-stationary random vibration analyses of long-span bridges exposed to seismic or wind excitationsIt has been shown that,the series of random vibration methods developed for seismic random analysis,energy-dissipation random analysis and buffeting random analysis of long-span bridges can effectively break through the bottleneck of traditional random vibration anaylsis methods with the restrictions of non-stationarity of random excitations,structural nonlinearity and computational scale.The developed methods are of high efficiency and ideal accuracy,and they will have a good prospect of engineering application.