An Enhanced Method For Non-Stationary Buffeting Response Of Long-Span Bridges

Non-stationary buffeting response analysis is an important part of wind resistance analysis of long-span bridges.In this thesis,the enhanced analysis method for the non-stationary buffeting response of long-span bridges under typhoon is investigated,including the development of a framework in the time-frequency domain to facilitate response analysis under non-stationary wind and an enhanced non-stationary buffeting force model based on that framework.The main work consists of two parts:The first part highlights the development of a framework in the time-frequency domain to facilitate response analysis under non-stationary winds.Based on the evolutionary power spectral density(EPSD),the responses of a structure due to non-turbulent and turbulent components of non-stationary winds are calculated separately and then combined to yield extreme of responses.The non-turbulent component of non-stationary winds is represented as time-varying mean speed modeled by normalized time function and vertical profile different from stationary winds.Time mean wind response is then solved statically by applying time-vary mean force given by a static transformation from time-varying mean wind speed.Probabilistic characteristics of the fluctuating response are solved in terms of the gust EPSD of non-stationary turbulence component and instantaneous aerodynamic transfer matrix reflecting transient wind-structure interaction,by using the pseudo excitation method involving transient structure dynamic effects.Alternatively,wavelet-based and the time-domain realization of the framework are also provided.Finally,the proposed framework is demonstrated by numerical examples,the results show that it can well predict the structural response under non-stationary wind.The second part presents an enhanced non-stationary buffeting force model for calculating typhoon–induced buffeting response of long-span bridges: the existing non-stationary typhoon wind model is first enhanced;a coherence transfer function matrix and time-dependent aerodynamic admittance function are introduced;and the nonlinearity in the buffeting forces resulting from the variations in the instant effective angle of attack and the non-uniform span-wise profile of the mean wind speed are considered in the enhanced model.The influence of the aforementioned enhancements in the non-stationary buffeting force model is finally assessed through the example of a long-span cable-stayed bridge subjected to Typhoon Dujuan.The results suggest that the enhanced EPSD model of tropical storm winds,non-linearity due to the instant effective angle of attack,and the variations in the velocity span-wise profile slightly change the buffeting responses.In contrast,introduction of the span-wise coherence of buffeting forces increases non-stationary extreme responses by 25-40%,and the time-dependent admittance function reduces the extreme responses as much as 70%.