Chapter 16 Statistical Tools for the Characterization of Environmental and Operational Factors in Vibration-Based SHM C. Rainieri, D. Gargaro, and G. Fabbrocino Abstract In recent years the interest in permanent monitoring of civil structures has raised because of the needs of controlling the ageing of a huge number of existing infrastructures. The recent advances in sensing technologies and data processing have made the installation and operation of permanent monitoring systems more and more attractive. Vibrationbased monitoring is based on the analysis of the evolution in time of damage features. A lot of these features are obtained from experimental estimates of the modal parameters. However, these estimates are usually influenced by environmental and operational factors. The variations they induce in the estimates may hide the small changes due to damage, so their influence has to be appropriately considered in practical applications. Using a large number of experimental data, models relating modal properties and environmental and operational factors can be set. However, the selection of the factors to be measured is typically not straightforward. As an alternative, statistical tools can be used to correct the estimates without the need to measure those factors. In the present paper, after a review of the available approaches to quantify the influence of environmental and operational factors, the opportunity of applying robust blind source separation techniques in this field is assessed. Keywords Vibration based Structural Health Monitoring • Natural frequencies • Environmental factors • Blind source separation • Second order blind identification 16.1 Introduction The recent increase in the number of applications of modal based damage detection techniques for Structural Health Monitoring (SHM) of civil structures takes advantage of the recent development of several algorithms for automated identification [1] and tracking [2] of modal parameters based on Operational Modal Analysis (OMA) methods. Damage detection techniques based on changes of the modal parameters of the monitored structure over time are well-established [3]. Thus, the continuous monitoring of modal parameters has a large potential in performance and health assessment of civil engineering structures [4]. Applications range from prompt detection of damage and degradation phenomena [5] to postearthquake health assessment and emergency management [6, 7]. An automated, accurate estimation of modal parameters also plays a primary role in the assessment of the dynamic behavior of complex structural systems such as geotechnical [8, 9] and historical structures [10, 11]. Extensive surveys and dedicated books are available in the literature about vibration-based SHM [4, 12, 13]. The monitoring process consists in the observation of the structure over long periods of time. Appropriate sensors and measurement systems continuously acquire records of the structural response; damage sensitive features are then extracted from the collected data and analyzed to assess the health state of the structure. From a general point of view, damage is defined as any change of the structure that adversely affects its performance [12]. This change can be in the form of stiffness change (for instance, cracking), mass change, connectivity change (for instance, looseness in a bolted joint) or boundary condition change (for instance, bridge scour). An effective SHM system should be able to automatically detect damage at an early stage [4]. Five damage detection levels have been defined [12]: • Level 1: identification of damage existence; • Level 2: localization of damage; C. Rainieri ( ) • D. Gargaro • G. Fabbrocino DiBT Department, Structural and Geotechnical Dynamics Laboratory StreGa, University of Molise, Viale Manzoni s.n.c, 86100 Campobasso, Italy e-mail: carlo.rainieri@unimol.it; danilo.gargaro@unimol.it; giovanni.fabbrocino@unimol.it © The Society for Experimental Mechanics, Inc. 2015 C. Niezrecki (ed.), Structural Health Monitoring and Damage Detection, Volume 7, Conference Proceedings of the Society for Experimental Mechanics Series, DOI 10.1007/978-3-319-15230-1_16 175
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