Field measurement and modal identification of a coupled floor slab system

This paper presents work on full-scale vibration tests of the second and third floor slabs of the Tin Shui Wai Indoor Recreation Centre. The concrete slabs are supported by one-way long span steel trusses and are connected by diagonal members and vertical columns to form a mega-truss. To determine the actual dynamic characteristics of the constructed slab system, ambient and forced vibration tests were performed. Thirty five setups were performed in the ambient vibration test to determine the mode shapes with a high spatial resolution. A recently developed Fast Bayesian FFT Method was used to identify the modal properties using the ambient data, where the mode shapes from individual setups were assembled by least square fitting. Forced vibration tests were performed by exciting the slabs with a long-stroke electromagnetic shaker, resulting in vibration amplitudes of the order of a few milli-g. A frequency sweep was carried out in the forced vibration tests and the modal properties were identified by least square fitting of steady-state amplitude spectra. The dynamic properties identified from the ambient and forced vibration tests will be compared and discussed.