| Transmission tower-line system is an important lifeline project as high voltage electric power's carrier. This structural system has some particular characteristics: with high-rise tower, large-span and crossing hypsography; the flexibility of entire structure increasing nonlinearly as its height; power transmission tower coupling with transmission lines with different amplitude of dynamic properties. Moreover, under stochastic environmental loadings, such as wind, rain and ice-accretion, etc., the dynamic responses behave as complexity, sensibility and high uncertainty. Therefore, environmental loadings are the main reasons why disaster accidents of transmission tower-line system occur frequently.According to the characteristics of environmental loading and structure system, and taking into account the wind gradient distribution profile, turbulence flow direction, intensity and power spectral density, the simplified wind field simulation method that is suitable for transmission tower-line system has been purposed respectively with the time series method and the harmonic wave superposition method. The tridimensional wind field is decomposed into mono-dimensional wind field effectively. According to the rule of cumulonimbus conformation and rainfall, the loading model for the rain acting on structures which includes rainfall quantity analysis and determination of rainfall velocity is established preliminarily with momentum theorem and Newton second theorem. Considering the characteristics of rainfall occurring simultaneously with random wind, the loading combination principles that include wind alone or wind together with rainfall act on structures are proposed, which make a fundament for loading input in numerical analysis of transmission tower-line system under fluctuating wind field.Taking into account all component characteristics of transmission line system, the principles and method for tower, insulator chains, transmission lines and boundary conditions modeling with finite element are systematically established. The procedure and corresponding parameters for wind-rain induced dynamic responses analysis of transmission line system in time domain are determined. Taking a typical disaster failure case under environmental loads as an example, the structural dynamic responses are comprehensively analyzed from different angles, i.e. from single tower to tower-line system, and from wind acting alone to wind-rain together acting. The results indicate that: since the dynamic properties of transmission tower have different amplitude orders comparing with those of transmission line, there is no significance of comparing them simply. Moreover, the primary question is to clarify the dynamic response contribution of transmission tower from transmission lines. Almost the majority of failure incidents of transmission tower-line system are caused for the sake of pressure-bending unstability under environment overloading. Thus, the case-hardened transmission tower should be enhanced properly in local components according to distribution characteristics of environmental loads in different regions when they are designed.Based on analysis of frequency domain, for the along-wind responses induced by environmental loads of transmission tower, the quasi-static gust response factor methods based on moment, shear and displacement are modified and expanded. The problems for calculation of load combination, response components and response factors are solved. The gust response factor method for transmission tower subjected to environmental loads is established elementarily. Take consideration with the rainfall loading action, the new connotations are endowed to the response components, so that the extension of gust response factor method is expanded. For the spatial response properties of transmission tower, the theoretical framework and application method for the quasi-static design with 3D gust response factor method is studied fundamentally. By means of measurement data from spot transmission tower, the analytical reliability and effectiveness of the gust response factor method is validated, and analyzing the sensitive influence factors related to the method.For the loop setting types and the characteristics of blunt icing cross section of conductor in cold climatically regions, the types and occurrence mechanism of across-wind vibration occurred on transmission lines are analyzed. Considering the sag effect of transmission lines, the criterion for icing conductor galloping acted by across-wind is formulated and expanded. The hybrid modeling and finite element modeling for bundle conductor vibration analysis in across-wind flow are established respectively with finite element method, and according to the property of eigenvalues of motion equations the method for judging unstable conductors galloping are discussed. Integrated with specific galloping analysis of certain bundle conductor setting, the rules impacting on across-wind galloping by the mechanic characteristics of transmission lines and properties of wind field turbulence, motion principle, influence factors and the type of bundle conductor galloping trace are disclosed primarily.On the premise that the reasons for fatigue damage occurrence and evolution and the mechanism of fatigue failure of transmission tower under environmental loads are systematically analyzed, in according to the accumulative fatigue damage theory and probabilistic distribution property of environmental loading effect of transmission tower, the analytical methods for structural fatigue damage and fatigue lifetime predication are supposed, furthermore, the influence factors on fatigue damage and fatigue lifetime are discussed. The analytical method for fatigue reliability of transmission tower is established on the bases of the first order two moment method and full distribution method respectively, which is controlled by the conditions of fatigue damage and designed lifetime. Based on the variational conditions including the hypothesis of stress kurtosis distribution, terrain, climate and environmental loading combination, the extents from the abovementioned influences on transmission tower fatigue reliability are assessed. The case analyses show that: the rainfall action has distinct adverse influences on structural fatigue reliability, which should not be neglected. |
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