Ambient modal identification of a coupled floor slab system

This paper presents work on fullscale vibration testing of the second and third floor slabs of the Tin Shui Wai Indoor Recreation Center. The slabs are supported by oneway long span steel tinsses, which are connected by diagonal members and vertical columns to form a megatruss. On 2/F are a large multifunction room and children play area, while the third floor hosts two basketball courts. Based on their expected usage, significant cultural vibrations with possible rhythmic activities can be expected. To determine the actual dynamic characteristics of the constructed slab system, ambient test was performed. Thirty five setups were earned out in the ambient test to determine the mode shapes with a high spatial resolution using six triaxial aceelerometers. 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. The dynamic properties identified from the ambient vibration test, as well as their posterior uncertainty and setup-to-setup variability, will be compared and discussed.