Structural Health Monitoring and Damage Identification Using Modal Flexibility-Based Approaches from Output-Only Vibration Data

An area of research in civil engineering that has received increasing attention in recent years concerns the application of vibration-based health monitoring and damage detection techniques on structures under ambient vibrations. The dissertation presents research investigations that were carried out in this field, by focusing mainly on building structures and on techniques that belong to a subclass of the modal flexibility (MF)-based methodologies for damage detection. According to these techniques, modal flexibility-based models of structures are estimated from vibration tests, and then, by applying inspection loads to such models, structural deflections are determined and used for detecting damage. Three main problems are addressed in the thesis. 1) In modal testing and identification of real-life structures not all the modes can be usually identified. MF-based deflections are thus estimated using incomplete modal models, leading to truncation effects. To address this problem, approaches are proposed to predict and reduce the truncation effects on MF-based deflections of building structures. 2) In the literature the damage detection methods based on MF-based deflections have been mainly developed for building structures that can be modeled as plane structures. In an attempt to extend these existing methodologies to more complex structures, research investigations were carried out on simple rectangular “box type” 3D building structures characterized by either plan-symmetric or plan-asymmetric configurations. 3) Modal flexibility can be only determined when mass-normalized mode shapes are available. However, such scaled mode shapes can not be directly estimated from output-only data. To address this problem, a MF-based approach for damage detection in building structures that can be applied directly on output-only data with minimal or no a-priori information on the masses is proposed. For all three analyzed problems, numerical simulations and experimental output-only vibration tests conducted on frame building structures were used to demonstrate the effectiveness of the proposed approaches.