Experimental Modal Analysis of Civil Engineering Structures

Decades ago, a major concern of structural engineers was the development and application of new and powerful numerical methods for the static and dynamic analysis of large civil engineering structures. The rapid development of finite-element techniques accompanied by tremendous technological progress in the field of personal computers allowed structural designers to use software packages for accurate simulation of structural behavior. However, the design and construction of more and more complex and ambitious civil structures, like dams, large cablestayed or suspension bridges, or other special structures have led structural engineers to develop new experimental tools to enable the accurate identification of the most relevant static and dynamic properties. These tools would provide reliable data to support calibrating, updating, and validating of structural analysis numerical models used at the design stage. The continuous ageing and subsequent structural deterioration of a large number of existing structures have encouraged the development of efficient vibration-based damage detection techniques supported by structural health monitoring systems. The natural tendency of civil engineering researchers was to utilize well established input-output modal identification techniques to accurately identify the main dynamic properties of civil structures. However, it is difficult to excite large civil structures in a controlled manner. Fortunately, remarkable technological progress in transducers and analog-to-digital converters has supported modal analysis of large structures exclusively based on measuring the structural response to ambient excitations and applying suitable stochastic modal identification methods. The main purpose of this article is to briefly present our perspective concerning the evolution of experimental modal analysis in the civil engineering field, from input-output to output-only modal identification techniques. This discussion is strongly influenced by our experience as researchers.