Experimental damage diagnosis of a model three-story spatial frame

Structural damage can be induced by a variety of events from short-term abnormal stresses to long-term natural aging. Detection of changes in a structure's ability to withstand subsequent loads can aid decisions on safety, repair, rehabilitation, and demolition. Dynamic property shifts can show internal cracks and minor damage before propagation or failure occurs, but only if a proper indicator is selected. In order to evaluate potential damage indices, a three-story metal frame building was constructed. Using Star Modal software, dynamic structural properties were obtained from modal decomposition on experimental tap test responses. The natural frequencies and mode shapes of the structure established an as-built baseline for comparison to ten other scenarios with removed bracing. Once modal properties for each case were determined, six unique damage indicators were applied to identical experimental data via twelve algorithms. The effectiveness of each damage detection technique was assessed, and final recommendations for the three-story model building were made. Of all the implemented algorithms, frequency response function (FRF) subtraction using the FRFs as a direct indicator is the most accurate damage detection scheme for the three-story test structure.