Field measurements of modal parameters for non-destructive damage detection algorithms

Over the last fifteen years state and federal transportation agencies have become increasing concerned with the deterioration of bridge structures. Structural deterioration and the probable reduction in performance, here defined as load capacity and remaining life, result from a variety of causal sources. These include the effects of overloading, strong motion excitation, age-induced fatigue cracking in steel structures, construction deficiencies, and material deterioration such as ASR reactions in reinforced concrete systems. Researchers and transportation agencies are attempting to develop automated procedures to evaluate and rate suspect structures, and need methods that provide direct indicators of damage level, location, and affect on performance. This paper addresses the initial measurement step in a modal-based Level IV non-destructive damage detection procedure. The paper describes instrumentation and measurement requirements unique to the above detection process. Several examples of measured data and necessary methodologies are presented.