Ambient Vibrations for the Dynamic Identification of Horizontal Diaphragms in Historic Buildings

The dynamic identification of horizontal diaphragms turns out to be one of the most difficult challenges in Civil Engineering and specifically in the field of Structural Health Monitoring (SHM). Characterising these macro-elements is important for the overall assessment of the building structural behaviour. This information is particularly valuable for unreinforced masonry constructions, often characterized by deformable diaphragms. Ambient vibration testing (AVT) could be very useful to obtain modal parameters without affecting the structure and describing the operating conditions of the entire system. The present work focuses on the AVT and Operational Modal Analysis (OMA) of a traditional Venetian slab, consisting of timber floor finishing with terrazzo flooring, in Ca’Tron, a significant noble palace overlooking on Canal Grande and valuable example of gothic architectural style. The slab was investigated at several acquisition points synchronously recording the response to ambient sources of vibration, through a passive seismic single station. A preliminary rapid processing of the data, through peak picking and Decò methodology allowed the identification of two modes, namely a transversal global mode and a vertical local mode of the floor. Their main modal parameters (i.e. natural frequencies, damping ratios and mode shapes) are presented and discussed.