Modern monitoring techniques contribute to accurately describing the structural health conditions of historical buildings and to optimizing the plan of maintenance as well as the restoring intervention. Particularly, dynamic testing gives knowledge about global structural behavior and can be used to calibrate numerical models and to predict the response to dynamic and earthquake loading. In some circumstances, vibration-based monitoring can also help in evaluating safety conditions. The present article proposes a discussion about the methodological multidisciplinary approach to modal testing when applied to architectural heritage buildings and structures, along with the description of selected case studies. These examples were chosen to cover the various issues connected to test design and interpretation.

To perform a realistic reliability analysis of a complex cable-stayed steel footbridge subject to natural hazard and corrosion, this article addresses a rational process of modeling and simulation based on identification, model updating, and validation. In particular, the object of this study is the Ponte del Mare footbridge located in Pescara, Italy; this bridge was selected as being a complex twin deck curved footbridge because it is prone to corrosion by the aggressive marine environment. With the modeling and simulation objectives in mind, a preliminary finite element (FE) model was realized using the ANSYS software. However, uncertainties in FE modeling and changes during its construction suggested the use of experimental system identification. As a result, the sensor location was supported by a preliminary FE model of the footbridge, although to discriminate close modes of the footbridge and locate identification sensor layouts, Auto Modal Assurance Criterion (AutoMAC) values and stabilization diagram techniques were adopted. Modal characteristics of the footbridge were extracted from signals produced by ambient vibration via the stochastic subspace identification (SSI) algorithm, although similar quantities were identified with free-decay signals produced by impulse excitation using the ERA algorithm. All these procedures were implemented in the Structural Dynamic Identification Toolbox (SDIT) code developed in a MATLAB environment. The discrepancies between analytical and experimental frequencies led to a first update of the FE model based on Powell's dog-leg method that relied on a trust-region approach. As a result, the identified FE model was capable of reproducing the response of the footbridge subject to realistic gravity and wind load conditions. Finally, the FE was further updated in the modal domain, by changing both the stationary aerodynamic coefficients and the flutter derivatives of deck sections to take into account the effects of the curved deck layout.

The focus of this work is on methods for modal identification of civil structures using output data only. An important family of time domain methods uses autoregressive time series models and exploits formulations developed in the field of system control. Another strategy consists of using methods well tested in the identification of structures on the basis of impulse response or free decay and extending them to the analysis of response signals generated by excitations of a more general nature. A third option refers to the Ho-Kalman minimal realization algorithm, which was extended by Akaike and Aoki to stochastic systems. These approaches, or their combinations, include a sizable proportion of the methods actually used in output-only identification of civil structures subjected to natural excitation, and most of them are based on stationarity assumptions. The question that prompted this study was as follows: what degrees of reliability and accuracy can such methods ensure when they are used, as i...