Full-scale dynamic testing and modal identification of a coupled floor slab system

This paper presents work on full-scale vibration testing of the 2nd and 3rd floor slabs of the Tin Shui Wai Indoor Recreation Center. The slabs are supported by one-way long span steel trusses, which are connected by diagonal members and vertical columns to form a mega-truss. On the 2nd floor are a large multi-function room and children play area, while the 3rd floor hosts two basketball courts. Based on their expected usage, significant cultural vibrations with possible rhythmic activities can be expected. To determine the dynamic characteristics of the constructed slab system, ambient and forced vibration tests were performed. Thirty-five setups were carried out in the ambient test to determine the mode shapes using six triaxial accelerometers. A recently developed Fast Bayesian FFT Method is used to identify the modal properties using the ambient data in individual setups. The mode shapes from the individual setups are assembled by a least square fitting procedure. Forced vibration tests were performed by loading the slabs at resonance with a long-stroke electromagnetic shaker, resulting in vibration amplitudes in the order of a few milli-g. A steady-state frequency sweep was carried out and the modal properties were identified by least square fitting of the measured steady-state amplitude spectra with a linear dynamic model. The dynamic properties identified from the ambient and forced vibration tests, as well as their posterior uncertainty and setup-to-setup variability, will be compared and discussed. The field tests provide an opportunity to apply the Fast Bayesian FFT Method in a practical context.