Date of Award
M.S. in Engineering Science
Elizabeth K. Ervin
Cristiane Q. Surbeck
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. Significant observations can be made about each mode shape based damage detection algorithm. Modal Assurance Criterion (MAC) is adequate for detecting incremental damage that affects the twisting motion of the structure. Although Coordinate Modal Assurance Criterion (COMAC) can predict general areas of damage, it has difficulty identifying exact damaged locations; however, it does effectively predict damage for the cumulative scenario. Modal curvature methods are not suitable for any case due to inaccuracy and occasional high frequency bias. Flexibility based methods are quite accurate for sequential damage but are not sensitive enough to detect cumulative damage. A major shortcoming, the story stiffness method can predict which global floor but not local element is damaged. 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.
Sabatino, Samantha, "Experimental Damage Diagnosis of a Model Three-Story Spatial Frame" (2011). Electronic Theses and Dissertations. 253.