Modal and seismic damage identification of a tall building model

This paper presents an experimental investigation on modal identification and seismic damage detection of a 38-story tall building model. The 1:20 scale reinforced concrete structure was tested on a threedirectional shaking table by exerting successively enhanced ground earthquake excitation to generate trifling, moderate, serious and complete (nearly collapsed) damage, respectively. After the earthquake excitation at each level, a 20-minute white-noise random excitation of low intensity is applied to produce ambient vibration response, from which modal properties of the tested structure in healthy state and after experiencing each of the four levels of earthquake excitation are identified. For comparison, the modal parameters are identified using both the random excitation and response, and using only the random response, respectively. With the identified modal parameters at each damage stage, three model-free damage indices, i.e., COMAC vector, normalized modal flexibility vector and modal curvature Z-value vector, are constructed for seismic damage evaluation. The predicted damage by these indices is compared with true damage observed during the tests.