This paper presents an overview of the research activities developed in the framework of the ReLUIS project founded by Department of Civil Protection (DPC) in 2017 and 2018 and focused to analyze some experimental accelerations made available by the Osservatorio Sismico delle Strutture (OSS), an Italian network of permanent seismic monitoring systems belonging to DPC. In particular, the recordings acquired by OSS on three selected masonry structures hit by the 2016/2017 Central Italy were acquired, analyzed and re-elaborated by a team of researchers from the

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The earthquake occurred on the 6th of April 2009 in the Abruzzo Region of Italy, seriously hit the Cultural Heritage (C.H.) patrimony with major destructive effects on L'Aquila, a city of 70,000 inhabitants with the size and the historical and strategic importance of the Region capital. The emergency activities to protect the C.H. have been developed on two parallel levels: (1) survey and assessment of damages, (2) implementation of temporary safety measures. The organization of the emergency actions was managed by a centralized structure, the so called Function 15 "Protection of Cultural Heritage", that coordinated the surveys of protected buildings and the design and implementation of temporary safety measures. This allowed the cooperation among different involved subjects (Ministry of Cultural Heritage officers, experts on structural engineering, architects and historians from Universities and private offices and fire brigade teams). The first level of the operating process was carried out on site by expert teams filling up dedicated survey forms for churches and palaces, developed by 123 106 Bull Earthquake Eng (2011) 9:105-138 Heritage); the forms were based on the standardization of damage survey allowing for its immediate interpretation. The second level was based on the past experience in the field of temporary safety measures; the idea was to provide a technical and scientific support in order to assist the work of fire brigade, highly experienced professionals in the "emergency" field. After the first emergency phase the damages of the most important buildings were more carefully investigated and the possible damage progression constantly monitored. The paper presents the case of the Spanish Fortress in L'Aquila, severely damaged by the earthquake; the description concerns the definition of the damages and the interpretation of the activated collapse mechanisms. Finally the design of the provisional strengthening interventions and the on site diagnostic investigations are presented.

The construction of reliable numerical models is a key aspect within the seismic assessment of existing unreinforced masonry buildings. However, it is also a complex process due to the many uncertainties involved that can affect the structural response. In situ tests allow for the acquisition of data at a local scale. Nonetheless, supplementary information representing the global response is necessary to overcome other uncertainties (i.e., wall-to-wall connections or floor stiffness). To this end, data from ambient vibration tests (AVT) are useful to support seismic assessments. In fact, they allow for the identification of dynamic structural properties, which are useful in refining the calibration of numerical models. In addition, they address solutions for the aforementioned uncertainties. In this context, the paper presents how to efficiently exploit AVT data by using the case study of the former Courthouse of Fabriano (Ancona, Marche). This structure has been monitored since 2010 by the Italian Department of Civil Protection with a network of 28 seismic accelerometers. As a result, the equivalent frame (EF) model was calibrated in the linear field thanks to the dynamic identification provided under operational conditions. Subsequently, nonlinear dynamic analyses were performed using the recordings acquired during the Central Italy earthquake in 2016/2017. Even if the building experienced only a slight nonlinear behaviour, this comparison between the simulated and actual seismic response made it possible to validate the EF model, especially with reference to the capability in reproducing the amplification phenomena, which is extremely important for the assessment of structural and non-structural components. K E Y W O R D Sdynamic identification, equivalent frame models, masonry structures, permanent monitoring, recordings from seismic eventsThis is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made.

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Ancient structures, especially very old ones, prove their soundness and the correctness of their structural layout by reaching our days in good conditions. This is the case of the Roman Arena in Verona—Italy, built in the first century A.D., and still standing in the historical centre of Verona. It became certainly the symbol of the city and it is open to public use for visits and also for operas, concerts and relevant shows. However, with a closer look, it is possible to appraise damages that the passing of time and the natural or man-induced events such as historical earthquakes and floods or wars and sieges left on the structure. Seismic events (the worst ones recorded in 1116, 1117 and in 1183) induced serious damages on the Arena since they caused the almost complete collapse of the third external ring of the monument, today only remaining in the so-called ‘‘wing’’ of the Arena, a freestanding curved wall composed by huge blocks of stone and characterized by a repetition of arches and massive pillars. With the purpose of evaluating the structural response of the Arena to static, dynamic (e.g. shows, concerts) and seismic loads, a structural health monitoring (SHM) system was installed in 2011, with a state-of-the-art technology to record meaningful data through a sensors’ network installed in relevant positions of the monument. A detailed crack pattern survey was carried out to identify main cracks and damages and select the most suitable positions for static sensors, able to control the reversibility of the seasonal displacements or deformations trends of the monument. Ambient vibration tests were also carried out to extract the fundamental modal parameters and calibrate/update reference finite elements models: global modes were identified and—with a special focus on the wing—acceleration sensors were installed in the areas where significant dynamic amplifications are expected according to the numerical simulation. The paper reports the preliminary activities carried out before the installation of the SHM system and illustrates the results of the first 1.5 year of monitoring analysing both the operational conditions of the structure and its response in case of exceptional events. Specific algorithms were developed and implemented to perform the continuous real-time treatment of static data and the automated identification of modal parameters

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Dynamic and vibration monitoring can be effectively implemented as a seismic assessment tool in case of an earthquake or natural disaster, where many buildings in a small area may be affected and damaged. In Italy, through the national network of the Seismic Observatory of Structures (OSS), the Department of Civil Protection (DPC) monitors the oscillations caused by earthquakes in 160 constructions of public property. The paper reports the research activities performed on three monitored structures of the OSS, affected by the Central Italy earthquake swarm of 2016 (max Mw=6,5). The three buildings (i.e. a school in Visso -MC, a former law court in Fabriano -AN and the city hall of Pizzoli -AQ) were constructed between 1920 and 1940 and are made of unreinforced masonry, with a good regularity in plan and elevation. Even though they present similar constructive features, the observed seismic-induced damages were largely different: heavy damages, near collapse, for Visso school; slightly damages for Pizzoli Municipality; and almost no damages for the building in Fabriano. The dynamic behavior of the monitored structures was studied through modal analysis techniques both under ambient vibrations and during the earthquake swarm. Data recorded by the monitoring systems are used to assess modal parameters variation and in particular to study the phenomenon of frequency and damping wandering during strong motion. Some severity indexes and dynamic parameters are calculated as well, including peak accelerations, structural amplifications, interstory drifts and elastic spectra. The results of modal identification will be used to assess the reliability of numerical models and their possible development to improve the predictive capacity in estimating the level of safety of existing structures.