In this study, the structural identification by ambient vibration tests is presented and the damage detection using the estimated modal parameters is carried out.
Most civil engineering structures, such as bridges, buildings and towers are susceptible to structural damage over their service lives due to the adverse loads and/or the structural deterioration, which requires proper maintenance of the structure. Many system identification methods by dynamic testing have been developed for the purpose of assessing the integrity of structures. Dynamic testing methods without any controled input are classified as ambient vibration tests. On the other hand the forced vibration testing incorporates methods where the excitation is artificially induced. Between two types of dynamic tests, ambient vibration test is easier to conduct since the structural response is measured while the structure is still in service. Artificial excitation systems, which may sometimes be complex and expensive, are not required.
In this study, modal parameters such as natural frequencies and mode shapes are obtained from dynamic response without input measurement by the direct Fourier analysis method and the random decrement method using band pass filter. A method for the damage assessment of structures by the inverse modal perturbation technique is also presented using the natural frequencies and the mode shapes measured at limited points. For more efficient damage assessment, the number of unknown probable damaged members are reduced for each identification by grouping the members in large structures. The effectiveness of the proposed methods is investigated through a series of experimental studies.