Investigation Of Modal Parameters’ Temperature Sensitivity And Strain Based Prewarning Method For Space Structure

Structural health monitoring (SHM) is regarded as an effective technique for structural damage diagnosis, structural safety and integrity assessment and structural service life evaluation, and modal identification and damage identification are both the core parts of SHM field. However, it is testified that environmental factors such as temperature can significantly affect the accuracy of estimated modal parameters and the effectiveness of damage sensitive indices. Meanwhile, space structures are rarely implemented with the SHM system and they are quite different from other structures such as bridges in both static and dynamic aspects. Therefore, studying the mechanism and relation between modal parameters and environmental factors and prewarning techniques of space structure are very significant. It is just these reasons that motivate this paper to investigate these problems for space structure- the China National Aquatics Center as follows.Principles of temperature effect on modal parameters have been theoretically illustrated and its effect on modal parameters has been categorized as variation of modulus of elasticity, structural geometry and inner force. A three span continuous beam with and without large boundary change has been employed as a structure to additionally explain how the three categories affect the modal parameter and by what proportion they respectively occupy in the variation of modal parameters.Based on the finite element model (FEM) of the China National Aquatics Center, both the dynamic characteristic of this space structure and relations between modal parameters and temperature have been investigated by simultaneously considering cases of structural global and local temperature distribution. For the global case, three cases, temperature induced variation of modulus of elasticity, inner force and integration of the both, are proposed to study temperature effect on modal parameters and two local temperature distribution cases have been carried out to study this problem for the local one.Using measurements from SHM system of the China National Aquatics Center, modal parameters of this space structure have been identified respectively by frequency domain decomposition (FDD) and natural excitation technique combining eigen-system realization algorithms (NExT+ERA), and relations between variations of modal parameters and temperature have been experimentally studied and conclusions obtaining from numerical analysis at chapter three have been experimentally verified.Employing actual strain response measurement, the Johnson transformation based statistical process control (SPC) has been proposed to assess the structural operation state and warn structural damage and unexpected excitement. The China National Aquatics Center is employed as a structure to validate this method in both numerical and experimental aspects. Deficiencies of this method and points that should been further investigated have been finally mentioned as well.