Structural and dynamic assessment and model updating of heritage buildings

The high seismicity of a large part of the European and, in particular, Italian territory requires effective measures in order to protect constructions at risk and to mitigate losses due to seismic events. This objective can be reached by increasing the knowledge of the dynamic behaviour of structures, particularly in the case of existing buildings and/or historical structures. Experimental modal analysis is becoming more and more relevant, above all in the case of important structures from the historical or architectural point of view, because of the unique structural techniques which affects a large part of these structures. In the last thirty years several techniques aimed at the experimental evaluation of the dynamic characteristics of structures have been developed: implemented first in the aeronautic field, their use has spread to various other fields such as robotics, mechanics, civil engineering. Beside the traditional techniques based on the knowledge of the input source, in recent years increased attention has been paid to procedures for modal parameters identification based on ambient vibrations. In fact, they allow to evaluate the dynamic properties of a structure under actual service conditions without any external excitation. As historical structures are concerned, output-only techniques are preferred because of smaller problems of test execution and input control, and because tests are cheaper and faster with respect to traditional experimental modal analysis and imply a minimum interference with the normal use of the structure. Identified modal parameters, representative of the structural behaviour in operational conditions, can be used to validate or update finite element models. The present paper describes the use of Operational Modal Analysis for the evaluation of the modal parameters of heritage structures. In particular, a specific application related to the Tower of the Nations, located into the Mostra D'Oltremare area in Naples, is reported. The need of designing an appropriate restoration and seismic upgrading intervention, taking into account the valuable characteristics of the structure itself, and, therefore, the need of improved knowledge of the structural characteristics of the building suggested to perform a dynamic identification test. The main results of experimental modal analysis and of analyses carried out in order to update the numerical model are herein reported and some aspects of the model optimization procedure are described. © 2008 by the Katholieke Universiteit Leuven Department of Mechanical Engineering All rights reserved.