Dynamic response of the Baptistery of San Giovanni in Florence, Italy, based on ambient vibration test

The dynamic behavior of the Baptistery of San Giovanni in Florence is evaluated using ambient vibration normally induced by wind, traffic, micro-seismic, and other human activities. We show how modal parameters of historical buildings can be estimated by the Enhanced Frequency Domain Decomposition (EFDD) in terms of natural frequency, damping ratio and modal shapes. We developed an automatic procedure to detect in real-time the modal parameters using three-component seismic stations. We show that displacement of the Baptistery can be automatically quantified for each single mode and we found that the first mode induces a displacement of ∼0.7 μm, 7 times larger than those produced by the 6th mode. We also show that after the vehicular traffic was blocked around the historical center, the daily urban activity in the rest of the city has enough energy to excite the first six modes of eigenmovements of this historical building and the daytime amplitudes of the eigenmotions are six times larger than those at night. Modal parameters are directly related to the mechanical characteristic and thus the ability of the presented methodology to automatically detect their evolution can be used to monitor in real-time the health of historical structures without affecting their functionality and making the method fast and cheap.