Influence of System Uncertainties on Structural Damage Detection by Ambient Vibrations

Abstract

The practical difficulties presented by forced vibration testing of large structures, such as transmission lines, led to an increased interest in structural monitoring through ambient vibrations, which usually allows the proper identification of modal properties. Typically, changes in these spectral properties constitute an indication of structural fault, which may then be assessed on the basis of experimental evidence. The authors proposed an approach to determine the stiffness matrices, which are essential to identify the location and intensity of damage. The approach requires ambient vibration data of all relevant coordinates used in the structural model, which are processed employing the SSI method. In practice, the identification method is seriously hampered by ambient factors such as temperature or humidity. In general those effects must be filtered out in other to obtain a reliable diagnosis of damage, approach that demands long term monitoring. In this paper, an alternative approach is explored, based on the introduction of error in stiffness matrices. Data on stiffness matrices is generated on the basis of observed variations of structural member stiffness caused by ambient factors. The influence of this uncertainty on the identified spectral properties is assessed by simulation.