Study On Wind-induced Vibration And Time-dependent Reliability Of Cable-suspended Pipelines

Wind load is one of the main loads to structure, especially when the span of pipeline is getting longer and longer, structure become more flexible and its wind-induced vibration response may become the key factor to structure design. At the same time, the long time continuous wind-induced vibration may cause fatigue damage to structure some parts such as nodes, supports and so on. When the fatigue damage reaches to its limit, may cause structure partial damage or integral destroy. Therefore, we should do research on the time-dependent reliability of cable-suspended pipelines(CSP) under the wind load with comprehensive consideration of strength and fatigue.Firstly, the wind velocity time-history of the CSP was simulated by inverse wavelet transform and the wind-induced vibration of the CSP was analysed using random vibration theory. At the same time, in order to study wind-induced vibration and time-dependent reliability of typical cable-suspended pipelines the random time-dependent mechanics model of this kind of structure has been stablished. Following the cumulative fatigue damage theory, the random time-dependent reliability of CSP under wind-induced vibration has been calculated. In addition, the crack propagation and fatigue damage of CSP under wind load in the case of the material which have initial crack have been analyzed using fracture mechanics method.The results show that: CSP are flexible structure system which have low natural frequency, and are sensitive to wind load; The displacement of CSP increases more and more rapidly as the average wind velocity increase along wind; The CSP may produce cross-wind resonance even the average wind velocity very small, but the key points stress changes of the main cable, suspended cable, stay cable are small, therefore, the alternative stress impact of the main cable, suspended cable's nodes on fatigue life can be ignored, when the pipeline under the cross-wind; The key points stress of the main cable, suspended cable far below its yield strength show that this structure has very strong wind-resistance ability; But this kind of structure may produce fatigue cumulative damage under the multiple repeated change wind load. Moreover, the material initial crack can intensify fatigue when the structures under the wind load.