Dynamic identification of a masonry building using forced vibration tests

The aim of the paper is to check the capability of dynamic identification procedures, usually applied to reinforced concrete or steel buildings, in the estimation of the dynamic characteristics of masonry buildings. To this purpose, the dynamic behaviour at low vibration levels of an existing masonry building subjected to forced, sinusoidal or sweep, vibration test, was investigated. Possibly on account of weak nonlinearities of the building, the measurements obtained with sinusoidal tests seemed more suited than those obtained by sweep tests for the application of identification techniques. These concern both modal and physical models: the dynamical characteristics of the building, the frequencies and some eigenvector components obtained by modal identification, were assumed as experimental data to update suitably selected stiffness parameters of a finite element model of the structure. The updating was performed by means of a specially developed dynamic identification code based on an output error equation. Criteria for a rational choice of physical parameters and measurements were applied. A very good agreement between numerical and experimental frequency response functions was obtained with the modal identification, while the physical model showed some rigidity in fitting all the experimental data, albeit with an acceptable level of scatter. Taken as a whole, the results show that well-established identification techniques can furnish useful information concerning the dynamic properties of existing masonry structures.