System identification of buildings by wave travel time analysis and layered shear beam models-Spatial resolution and accuracy

A previously explored method for one-dimensional structural system identification and earthquake damage detection in buildings, based on measuring wave travel time through the structure and its changes, is formalized, and its spatial resolution and accuracy are analyzed. The method identifies the velocity of propagation of shear waves in the structure as function of height. The wave travel time is measured from impulse responses obtained from recorded response at different locations in the structure. The main advantages of this SHM method over other methods are its robustness in application to real buildings and large amplitude response, insensitivity to the effects of soil–structure interaction, and local in nature achieved with relatively small number of sensors. The identification is based on a layered shear beam model of the building. In this paper, analytical impulse response functions are presented for such model, which provide theoretical basis to define identification algorithms. The derivation of one such algorithm, which involves approximations, from the exact wave propagation solution of the model is presented, and its spatial resolution and accuracy are critically examined. Termed here ‘direct algorithm’, it involves measuring the pulse time shifts and amplitudes and identifies shear wave velocities and quality factor Q in the layers. Various issues identified, e.g. the trade-off between accuracy and detail of the identification, are illustrated on a full-scale densely instrumented nine-story RC building (Millikan Library in Pasadena, CA, USA, excited by 2002 Yorba Linda earthquake).