Dynamic testing of civil infrastructure is required for reasons ranging from, for example, checking performance of new or retrofitted structures, evaluating and predicting vibration serviceability, calibrating structural models and establishing baseline performance for structural health monitoring. There are also, in limited cases, possibilities to identify, characterise and diagnose structural defects. For the above reasons and with increased interests in performance of constructed facilities, challenging new applications for dynamic testing are found and met with improving technology. Together with advances in instrumentation capabilities, there have been in the last decade great advances in techniques for system identification, allowing for effective dynamic testing of practically any kind of structure. Among dynamic testing technologies, forced or artificial excitation of civil structures and system identification procedures borrowed from mechanical/aerospace disciplines have proven ability to identify true mode shapes in the most demanding conditions (strong noise, large scale and having closely spaced, complex and even nonlinear modes). At the other end of the spectrum, operational modal analysis (OMA) now has proven capabilities for structures where forces cannot be applied or used effectively, to the extent that OMA now appears to be the preferred choice. We find that in some cases both procedures may be required for full identification, and a hybrid form that uses a mix of artificial and ambient excitation has been developed in order to extract the missing mode scaling (mass) parameter for OMA. The paper presents a sample of techniques in different applications to bridges, illustrating strengths and weaknesses, to provide engineers with information to understand the process of dynamic testing and appreciate the validity of the results.
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