Field measurement and Bayesian modal identification of a primary-secondary structure

The Mong-Man-Wai Building (MMW) is a seven-storied reinforced concrete building situated on the campus of the City University of Hong Kong. On its roof a two-storied steel frame has been recently constructed to host a new wind tunnel laboratory, forming a primary-secondary structure. This paper presents field instrumentation and modal identification of the structural system. A number of setups were carried out to cover all locations of interest using a limited number of triaxial sensors. Ambient vibration measurements were obtained and modal identification was performed using a Bayesian FFT Approach. The approach views modal identification as an inference problem where probability is used as a measure for the relative plausibility of outcomes given a model of the response and measured data. The modal identification results reveal a number of interesting features about the building and the roof frame. Five modes are presented in this paper, exhibiting the dynamics of the primary and secondary structure as well as their coupling. Selection.