For Structural Health Monitoring (SHM), a core prerequisite is to accurately identify the modal properties. Since the dynamic characteristics of a structure change under the effects of different environmental factors such as temperature and wind, it is necessary to determine how the environmental factors affect the modal properties. This study focuses on the Guangzhou new TV tower (GNTVT), which is a 610-m high structure. Based on the measured data from GNTVT, both the varying patterns of the operational modal parameters under the effects of different environmental factors and the Finite Element Model (FEM) updating based on Genetic Algorithm (GA) had been investigated. Then, using the updated FEM, the effect of the temperature on the modal frequency had been investigated under two situations: (1) Temperature only affects the modulus of elasticity. This situation was considered to be more important because of the significant frequency change. When temperature increases by10 • C, the maximum change of modal frequencies is 1%. (2) Temperature only affects the geometric stiffness of structure. This situation was considered to be less important because the change in the frequency is very small which may be ignored.When temperature increases by10 • C, the maximum change of modal frequencies is 0.02%. The simulated results were consistent with the measured results. KEYWORDS finite element model, modal frequency, model update, super high-rise structure, temperature
INTRODUCTIONUsing the vibration-based method, the primary task of Structural Health Monitoring (SHM) is to accurately identify the structural modal properties. This is because the modal properties, eg, frequency, modal shape, and damping ratio, can accurately reflect the structural properties such as stiffness and damage. 1,2 However, changes in the environmental conditions may cause changes in these modal properties. Over the past two decades, using field measurements and dynamic tests, the effects of the environmental factors, such as temperature, wind speed, and humidity on the structural modal properties have been extensively investigated. 3-17 While the vibration-based structural damage identification approaches have gained increasing attention in research, earlier studies have shown that the environmental effect is one of the main pitfalls limiting successful applications of the vibration-based damage detection methods to real structures. [18][19][20] These studies concluded that: (1) the effect of the variations in the modal properties due to the changes in the environmental factors is highly significant. The effect may be even greater than that caused by structural damage.(2) Temperature is the environmental factor that causes severe variation in modal properties.(3) The effect of the temperature on the natural frequencies can be eliminated using intelligent artificial algorithms such as Artificial Neural Networks (ANN) and Supporting Vector Machine (SVM).The studies mentioned in the preceding literature review are mostly based on the monitoring data ...