System identification of a 13-story reinforced concrete building through ambient and forced vibration

Abstract

This paper describes a unique research program that investigated the dynamic behavior of a full scale 13-story reinforced concrete building under forced vibration, ambient vibration and distal earthquake excitation. Modal parameters of the building were identified using the System Identification Toolbox (SIT) developed at the University of Auckland, New Zealand utilizing a range of methods in both the frequency and time domain. Initially, an eccentric mass shaker located on the upper floor of the building was used to excite the building while instrumented with eight accelerometers. Ambient vibrations were then recorded over a period of two weeks utilizing over 40 tri-axial accelerometers. During this period the building was also excited by a M6.5 earthquake roughly 350km away and high quality acceleration data was recorded. System identifications were carried out using test data from each excitation source, and comparisons were made between the results of each. Correlation of mode shapes was evaluated using the modal assurance criterion (MAC) and the variation in the natural frequency and damping values were statistically evaluated. Overall, consistent results were observed for modal parameters obtained from various methods. The influence of the excitation force characteristics on the performance of various system identification techniques was also investigated.