A new method for earthquake-induced damage identification in historic masonry towers combining OMA and IDA

This paper presents a novel method for rapidly addressing the earthquake-induced damage identification task in historic masonry towers. The proposed method, termed DORI, combines operational modal analysis (OMA), FE modeling, rapid surrogate modeling (SM) and non-linear Incremental dynamic analysis (IDA). While OMA-based Structural Health Monitoring methods using statistical pattern recognition are known to allow the detection of small structural damages due to earthquakes, even far-field ones of moderate intensity, the combination of SM and IDA-based methods for damage localization and quantification is here proposed. The monumental bell tower of the Basilica of San Pietro located in Perugia, Italy, is considered for the validation of the method. While being continuously monitored since 2014, the bell tower experienced the main shocks of the 2016 Central Italy seismic sequence and the on-site vibration-based monitoring system detected changes in global dynamic behavior after the earthquakes. In the paper, experimental vibration data (continuous and seismic records), FE models and surrogate models of the structure are used for post-earthquake damage localization and quantification exploiting an ideal subdivision of the structure into meaningful macroelements. Results of linear and non-linear numerical modeling (SM and IDA, respectively) are successfully combined to this aim and the continuous exchange of information between the physical reality (monitoring data) and the virtual models (FE models and surrogate models) effectively enforces the Digital Twin paradigm. The earthquake-induced damage identified by both data-driven and model-based strategies is finally confirmed by in-situ visual inspections.

Operational Modal Analysis, Model Update and Fragility Curves Estimation, through Truncated Incremental Dynamic Analysis, of a Masonry Belfry

Masonry towers, located in seismic zones, are vulnerable and prone to damages up to compromise their stability. The scatter of data on the mechanical properties of masonry, geometry and boundary conditions determine a lack of building knowledge on their expected behaviour. Therefore the assessment of the seismic capacity represents a critical task. This paper contributes to the issue of seismic analysis of masonry towers, focusing a meaningful case study: the St.Silvestro belfry in L’Aquila, Italy. The tower, severely damaged by the 2009 earthquake sequence, underwent extensive restoration works, endeavoured to mitigate its vulnerability. The observed seismic damage, the performed no-destructive testing campaign and the accomplished rehabilitation measures are described in the paper. The authors appraised the actual seismic performances of the St.Silvestro belfry, reinforced by the last restoration works. At first, the Operational Modal Analysis (OMA) is carried out to enhance building knowledge. In a second step, a refined finite element model is calibrated on the results from OMA to seize the actual dynamic response. Ultimately, by using the updated finite element model, the authors estimate the fragility curves in terms of peak ground acceleration using truncated incremental dynamic analyses.

Implementation of Pushover Analysis for Seismic Assessment of Masonry Towers: Issues and Practical Recommendations

Seismic assessment is a paramount issue and a valuable instrument towards the conservation of vulnerable structures in seismic prone regions. The past seismic events have highlighted the vulnerability of masonry towers that is exhibited by severe structural and nonstructural damages or even collapses. The preservation of existing structures, mainly focused on the built heritage, is emerging and imposing substantial enhancements of numerical methods, including pushover analysis approaches. The accuracy of the estimated seismic capacity for these structures is correlated with the assumed strategies and approximations made during the numerical modeling. The present paper concerns those aspects by exploring the limitations and possibilities of conceiving pushover analysis in the finite element method environment. The most crucial target is tracing in a pushover capacity curve the corresponding initiation of structural damages, maximum load-bearing capacity, and the ultimate displacement capacity. Different recommendations for achieving this target have been proposed and illustrated for practical utilization. Three representative geometrical towers, adopting three different materials and five different load patterns, are investigated in this study. The load pattern’s role and necessity of the displacement-like control approach for the pushover analysis are exploited. This paper highlights the load-bearing capacity overestimation when the force-controlled are implemented. The material model influences the achievement of softening branch with a distinguishable displacement capacity.

Seismic Upgrading of a Historical Masonry Bell Tower through an Internal Dissipative Steel Structure

Masonry towers are part of a valuable architectural heritage characterizing the landscape of many historical areas. These towers are vulnerable structures that are prone to earthquake damage. Hence, the design of effective seismic upgrading interventions is an important task for preserving such architectural forms for future generations. In view of that, the objective of this study is to contribute a possible addition to the portfolio of available approaches for seismic upgrading of masonry towers. This goal was pursued by exploring an innovative structural solution that does not alter the external appearance of the tower and its static scheme under gravity loads, yet is able to increase its capacity to withstand seismic actions through added damping. Specifically, the proposed solution consists of a steel structure internal to the masonry tower that incorporates fluid viscous dampers. In order to evaluate its potentialities, a real case study was taken as a testbed structure, historic analysis as well as geometric and architectural surveys were undertaken, an initial design for the upgrading was made, and numerical simulations were performed. The obtained results, although preliminary, highlight the potentialities of the proposed structural solution for the seismic upgrading of masonry towers and might open the way to future developments and applications.

Historical Masonry Towers: Overview, Seismic Vulnerability, Behavior During an Earthquake, Seismic Strengthening

The article provides an overview of historic masonry towers such as the minarets of mosques, bell towers of churches, clock towers, leaning towers, so-called "falling towers" and ruined towers. It was considered what kind of masonry, what kind of mortars the Romans, the ancient Egyptians, the Inca and Mayan cultures in America used. Some aspects of seismic vulnerability of masonry towers were studied. The modes of destruction of thin masonry structures, mechanisms of destruction of masonry in towers are considered, the seismic behavior of historical masonry towers are considered, and one of the methods of seismic strengthening using an innovative "smart" material is presented.