Luca Zanotti Fragonara

Global Sensitivity-Based Model Updating for Heritage Structures

Sensitivity-based approaches to model updat- Q2 ing have become widely used because of their capability to calibrate the model by taking into account the influence of updating parameters associated to different structural elements. Global sensitivity analysis (SA) allows model updating to be carried out even in the case of elevated un- certainty about the material characteristics. Architectural heritage structures deserve specific attention on account of their intrinsic geometrical complexity and heterogene- ity. In this article, the concept of global SA is applied for the first time to complex monumental structures, and a comparative view is offered on more classical local sen- sitivity approaches. Different finite element (FE) calibra- tion techniques—via global and local SA—were applied to the intriguing case of the church of S. Maria del Suf- fragio in LAquila (Italy), severely damaged by the 2009 earthquake. The FE updating was based on experimental data acquired by a dynamic monitoring system. Finally, calibration strategies were assessed through time history analyses by comparing the responses to the recorded seismic event.

Vibration-Based Monitoring and Diagnosis of Cultural Heritage: A Methodological Discussion in Three Examples

ABSTRACT 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.

Dynamic Characterization of Complex Masonry Structures: The Sanctuary of Vicoforte

Forecasting the response to dynamic and earthquake loading, for safety assessment as well as for control purposes, may benefit from vibration measurements, which are indispensable to update a mathematical model. The viability of ambient vibration testing for complex masonry structures is demonstrated here in a relevant case study of the Sanctuary of Vicoforte, near Mondovì, Italy. This monument is of great architectural significance, characterized by the largest elliptical dome in the world (axes 37.15 m × 24.80 m). Conceived in 1596 by Duke Carlo Emanuele I to serve as the mausoleum of the Savoy dynasty, the monument was affected since the earliest stages of its construction by the settlements of foundations, resulting in the opening of extensive cracks. In 1983, its dome-drum system was strengthened for fear of an imminent collapse. Since 2001 a research project has been conducted to evaluate the state of conservation and structural safety of the building. After a short description of the activities carried out to determine the structural conditions of the building, this study illustrates the salient stages of the dynamic characterization.

Unscented Kalman Filter for Non-Linear Identification of a New Prototype of Bidirectional Tuned Vibration Absorber: A Numerical Investigation

Several nonlinear system identification methods have been presented in the past, such as the Extended Kalman Filter, the H filter and the Sequential Monte Carlo methods. One of the most promising ones is the Unscented Kalman Filter (UKF) recently proposed for the on-line identification of structural parameters. In the present study the UKF is proposed to the purpose of the nonlinear identification of a new prototype of rolling-pendulum tuned vibration absorber which, relying on an optimal three-dimensional guiding receptacle, can simultaneously control the response of the supporting structure along two orthogonal horizontal directions. Unlike existing ball vibration absorbers, mounted on spherical recesses and used in axial-symmetrical structures, the new device can be bidirectionally tuned to both fundamental structural modes even when the corresponding natural frequencies are different, by virtue of the optimum shape of the rolling cavity. Based on preliminary numerical simulations, the UKF is shown to be effective in identifying the structural parameters of the new device and particularly the nonlinear rolling friction dissipation mechanism at the interface between the ball bearing and the rolling surface.

Assessment of the seismic vulnerability of an old RC viaduct with frame piers and study of the effectiveness of base isolation through PsD testing

The RETRO project aims at studying the seismic behaviour of existing reinforced concrete bridges (RC) and the effectiveness of innovative retrofitting systems. Emphasis has been paid on old bridges generally not properly designed for seismic action. On the basis of a previous experimental campaign consisting of cyclically imposed displacements on 1:4 reduced scale models of a frame pier, belonging to a typical old RC highway viaduct, a new experimental activity has been proposed. Two specimens (scale 1:2.5), a frame pier of 2 levels (height 5.8 m) and a frame pier of 3 levels (height 10.3 m), have been built and tested using the PsD technique with sub-structuring technique, including the modelling of the entire viaduct to which they belong. Two test configurations have been considered: 1) retrofitted viaduct using Friction Pendulm Isolators, and an 2) as-built configuration imposing a Serviceability and Ultimate limit state conditions. For each phase of the experimental campaign model identification has been performed. The aim of the campaign was twofold: 1) increasing the knowledge on the non-linear behaviour of RC frame piers in presence of plain steel bars and detailing of the late 1950s for which few studies have been carried out, and 2) study the effectiveness of seismic isolation systems for the seismic response mitigation