EVALUATING STRUCTURAL DETERIORATION BY DYNAMIC-RESPONSE

The dynamic response of two C 3 x 4.1 channel steel beams is evaluated in terms of the reduction in load-carrying capacity of the damaged st ate versus the undamaged stage. The beam specimens are sized and confi gured to have similar frequency response observed in actual bridges. E ach beam is subjected to different damage scenarios, i.e., various typ es, locations, and degree of damage. For each scenario, the characteri stics of the dynamic response are determined from acceleration measure ments made during low-level free-vibration tests. A finite-element mod el was used to calculate the dynamic response of the simulated damaged structures. The experimental and analytical results are scrutinized t o correlate increasing deterioration and changes in the dynamic respon se. Good correlations are found between the experiments and analysis. For each damage scenario, the yield and ultimate-load capacities of th e test beams are defined by a damage index. Both experimental and nume rical results indicate that there is less than 10% change in the natur al frequencies at critical damage state.