Evaluating Structural Deterioration by Dynamic Response

The dynamic response of two C 3 × 4.1 channel steel beams is evaluated in terms of the reduction in load-carrying capacity of the damaged state versus the undamaged stage. The beam specimens are sized and configured to have similar frequency response observed in actual bridges. Each beam is subjected to different damage scenarios, i.e., various types, locations, and degree of damage. For each scenario, the characteristics of the dynamic response are determined from acceleration measurements made during low-level free-vibration tests. A finite-element model was used to calculate the dynamic response of the simulated damaged structures. The experimental and analytical results are scrutinized to correlate increasing deterioration and changes in the dynamic response. Good correlations are found between the experiments and analysis. For each damage scenario, the yield and ultimate-load capacities of the test beams are defined by a damage index. Both experimental and numerical results indicate that there is less than 10% change in the natural frequencies at critical damage state.