The impact of uncertainty in operational modal analysis for structural identification of constructed systems

Abstract

Structural identification (St-Id) may be defined as the parametric correlation of structural response characteristics predicted by a mathematical model with analogous quantities derived from experimental measurements. Advancement in analytical and experimental technologies fostered the St-Id research since its introduction to engineering mechanics in mid-seventies. Even though those efforts resulted in successful application examples in aerospace and automotive industries, possible benefits of St-Id has not been enjoyed in management of large constructed systems such as highway bridges and tunnels.It is generally acknowledged that most critical infrastructure systems have been falling short of providing satisfactory operational performance under everyday demands, and their constructed elements have been appraised to have poor structural conditions. In the last decade there has been a great thrust for objective condition assessment, and non-destructive evaluation methods. Finite element modeling has evolved as the primary mathematical modeling tool for descretization of complex constructed systems, as experimental modal analysis has become a mature experimental technique for mathematical model updating.Operational modal analysis is a new term encompassing modal analysis methods that use output-only measurements and it has drawn a lot of interest mainly because of its relative ease of applicability on large structures. A number of research studies on real structures revealed that complexities related to inherent uncertainty mechanisms in constructed systems limit the reliably of the identified modal properties. Even though the adverse impacts of uncertainty in operational modal analysis and St-Id have been addressed in the literature there has not been a systematic attempt to investigate them.This thesis has been structured to provide an insight into relative impacts of different uncertainty sources in operational modal analysis. Uncertainty impacting operational modal analysis was grouped into four categories: (1) Structural complexity, (2) Characteristics of random excitation, (3) Signal preprocessing approaches (4) Modal parameter identification algorithms.Results of the study showed that each category of uncertainty and their sub-categories have different levels of impact on the final results and the ultimate success in an operational modal analysis study on a constructed system is governed by how well the uncertainties are mitigated during the study.%%%%Ph.D., Mechanical Engineering and Mechanics – Drexel University, 2006