Research Of Method And System Of Civil Structural Health Monitoring Based On Modal Analysis

Damage in structures can be defined as a reduction of the structural bearing capacity during their service period. This reduction is usually caused by degradation and deterioration of structural components and/or connections. All load-carrying structures, such as buildings, bridges and offshore platforms continuously accumulate damage during their service life. Undetected damage may lead to structural failure and loss of human lives. Structural Health Monitoring (SHM) is the process of implementing a damage detection strategy. The SHM process involves the observation of a system over time using periodically sampled dynamic response measurements from an array of sensors. The extraction of damage-sensitive features from these measurements and the statistical analysis of these features are then used to determine the current state of system health. Visual inspection is the most common method for structural damage detection. This method, however, is unreliable for complex structures because certain critical damage may occur in inaccessible areas or may be concealed by paint or skin. Visual inspection also cannot provide a quantitative value for the remaining strength of the structure. Other non-destructive evaluation (NDE) methods have been employed to assess the integrity of a structure, including radiographic, fibre optic, X-ray, acoustic emission, and ultrasonic techniques. These traditional NDE methods, however, only give the effective deterioration state of local areas and tend to be impractical for large complicated structures. Additionally, none of these approaches provide a quantitative assessment of the damage magnitude.Change in structural properties due to damage subsequently affects the dynamic behavior of structures, while the latter can be measured by vibration experiments in the field. It is, therefore, natural to use the measured changes in dynamic behavior for the identification of structural damage. By using thevibration-based methods, damage can be detected in a global sense even when the location of damage is inaccessible. The damage detection methods based on vibration data were initially investigated in mechanical, aerospace and offshore engineering. This technique has received increasing interest in civil engineering in recent years. Although successful applications have been developed recently, the damage assessment of complex structures such as buildings and bridges remains a challenging task for civil engineers. Damage or fault detection, as determined by changes in the dynamic properties or response of structures, is a subject that has received considerable attention in the literature. The basic idea is that modal parameters (notably frequencies, mode shapes, and modal damping) are functions of the physical properties of the structure (mass, damping, and stiffness). Therefore, changes in the physical properties will cause changes in the modal properties. Based on the structure vibration measurement, this paper deeply analyzes the method of the structural damage detection. With the actual civil structure being research object, the paper focus on vibration signal acquisition, modal analysis and parameter extraction methods, and makes research on structural damage detection methods by utilizing structural modal parameters. The complexity and feasibility of implementing methods are also discussed in detail. The current status and future development of engineering application for structural damage detection are expounded.