Movable guyed masts affected by wind loads: Buckling and stochastic response

This paper presents a new structural system to be used in communication towers and demonstrates the achieved improved structural performances with respect to currently used cable-stayed masts. The proposed structure is a cable-stayed tower where a truss system is introduced as a new link between the cables and the mast in order to improve the lateral stiffness and to reduce instability phenomena. The motivations and the main design choices for such a supporting structure are outlined. Numerical models are developed in order to accurately describe the geometrically nonlinear behavior of both the cables and the whole system. A combined linear/nonlinear stability analysis is proposed to investigate the structural stability of the system and the Monte Carlo simulation approach is used to estimate the stochastic response of the supporting structure to a correlated Gaussian vector describing the wind load. The obtained results manifest the better performances achievable by introducing the truss system. Copyright © 2008 John Wiley & Sons, Ltd

ambient vibration testing of a monumental fountain by contact and non contact sensing techniques

Abstract Ambient Vibration Testing (AVT) and Operational Modal Analysis (OMA) are widely accepted non-invasive diagnostic tools for investigating the actual dynamic behavior of full scale structures and for extracting useful information for the optimal tuning of numerical models. However, despite many successful applications in the case of bridges and slender buildings, ambient vibration testing is still rarely carried out on historical heritage buildings, with a few documented applications on slender structures such as civic and bell towers. In this paper, the authors aim to investigate the potential of AVT and OMA when applied to unconventional heritage structures. In particular, dynamic testing and operational modal analysis of a monumental fountain, the "Fontana Maggiore", in the City of Perugia, Italy, is presented using data acquired by both contact and non-contact sensing techniques. Results also allow to comment on the most suitable sensing hardware for the considered application

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

AbstractThis 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

dynamic characterization of a severely damaged historic masonry bridge

Abstract The paper presents the preliminary results of an ongoing research on a masonry arch bridge in the neighborhood of Todi (Umbria, Italy). A multidisciplinary approach integrating geometric survey, dynamic testing and numerical modeling is presented aimed to assess the structural performance of the ancient bridge. A photogrammetric survey based on high resolution images provided by UAV (Unmanned Aerial Vehicle) has been processed in order to obtain a 3D numerical model and to map the crack layout. Ambient and forced vibration tests have been carried out using laser vibrometer, radar interferometer and seismic accelerometers. Experimental data have been processed by operational modal analysis and the results have been compared with the numerical results given by a simplified model

On the accuracy of UAV photogrammetric survey for the evaluation of historic masonry structural damages

Abstract Photogrammetric surveys via Unmanned Aerial Vehicles are nowadays a valuable tool for historic masonry structures inspection, surveillance, mapping and 3D modeling issues. When structural damage mapping and structural assessment are of interest obtaining accurate and reliable geometric models is a crucial issue. Therefore, the flight plan, the georeferencing and the data processing steps need to be properly designed. In this paper, a procedure for the photogrammetric survey via Unmanned Aerial Vehicles of a masonry structures is used in order to obtain effective visual inspections and a 3D model of a historic masonry arch bridge located along the ancient Via Amerina (Todi, Perugia, Italy). The photogrammetric survey provides a detailed representation of the actual geometry, including lack of volumes and significant cracks along the vault and the spandrel walls, outlining a severe damage state affecting all the structure. Finally, a Total Station and a Laser Scanner were used to compare the results obtained by photogrammetry, highlighting the advantages, the limits and the weaknesses offered by their use

Detecting earthquake-induced damage in historic masonry towers using continuously monitored dynamic response-only data

The paper summarizes the results obtained during the continuous dynamic monitoring of two iconic Cultural Heritage towers -the Gabbia tower in Mantua and the San Pietro bell-tower in Perugia. The two towers, exhibiting different architectural and structural characteristics, were monitored over a similar time period (of about 2 years) by Politecnico di Milano and University of Perugia, respectively, and similar methodologies of automated operational modal analysis and structural health monitoring were adopted by the two Research Teams. During the monitoring, both the towers underwent far-field seismic events which caused slight structural damage. In both case studies, the limited number of accelerometers installed in the towers allows the tracking of automatically identified modal frequencies and to distinguish between environmental and damage effects on the natural frequencies. Furthermore, the occurrence of structural anomalies corresponding to small drops in frequencies is confirmed through multivariate statistical analysis, based on principal component analysis and novelty detection

calibration of finite element models of concrete arch gravity dams using dynamical measures the case of ridracoli

Abstract Accurate and reliable predictions of the dynamic behaviour of dams is essential to ensure their correct management and the safety of the downstream population. In this context, structural monitoring and testing procedures for their dynamic characterization are essential tools for the calibration of numerical models of dams. This paper presents some results of an ongoing research program aimed at an accurate definition of the geometric and structural properties of a large arch-gravity dam: the Ridracoli dam in the Emilia-Romagna region, Italy. In the first part of the research, a detailed survey carried out by an Unmanned Aerial Vehicle has allowed the detailed reconstruction of the three-dimensional geometry of the structure. The dense point cloud, as provided by the aerial survey, has been the base for the definition of a high-fidelity finite element model, including the dam, the surrounding rock mass, with a detailed reconstruction of the site topography, and the reservoir water, whose dynamic interaction with the structure is modelled by means of acoustic elements. A large program of structural monitoring, including a number of vibration tests, has been performed on the Ridracoli dam during the last thirty years. The dynamic monitoring system includes accelerometers, located in the structure and in the foundation rock mass, strain gauges and hydrodynamic pressure cells. The forced vibration tests were carried out in correspondence to the maximum water level, in order to identify the dynamic characteristics of the dam. The mechanical properties of the dam material and of the foundation rock are calibrated by comparing model predictions with the results obtained from vibration tests and from acceleration recordings acquired under recent seismic events, considering the actual water levels registered during the tests. The finite element model obtained will allow the simulation of the seismic performance of the dam under different design earthquakes. The assessment of the effects of the reservoir level and of the vertical joints on the dynamic response of the structure will be analysed

Full-scale testing of a masonry building monitored with smart brick sensors

The seismic monitoring of masonry structures is especially challenging due to their brittle resistance behavior. A tailored sensing system could, in principle, help to detect and locate cracks and anticipate the risks of local and global collapses, allowing prompt interventions and ensuring users' safety. Unfortunately, off-the-shelf sensors do not meet the criteria that are needed for this purpose, due to their durability issues, costs and extensive maintenance requirements. As a possible solution for earthquake-induced damage detection and localization in masonry structures, the authors have recently introduced the novel sensing technology of "smart bricks", that are clay bricks with self-sensing capabilities, whose electromechanical properties have been already characterized in previous work. The bricks are fabricated by doping traditional clay with conductive stainless steel microfibers, enhancing the electrical sensitivity of the material to strain. If placed at key locations within the structure, this technology permits to detect and locate permanent changes in deformation under dead loading conditions, associated to a change in structural conditions following an earthquake. In this way, a quick post-earthquake assessment of the monitored structure can be achieved, at lower costs and with lower maintenance requirements in comparison to traditional sensors. In this paper, the authors further investigate the electro-mechanical behavior of smart bricks, with a specific attention to the fabrication of the electrodes, and exemplify their application for damage detection and localization in a full-scale shaking table test on a masonry building specimen. Experimental results show that smart bricks' outputs can effectively allow the detection of local permanent changes in deformation following a progressive damage, as also confirmed by a 3D finite element simulation carried out for validation purposes. Related video presentation available here

CALIBRATION OF NUMERICAL MODELS TO SUPPORT SHM: THE CONSOLI PALACE OF GUBBIO, ITALY

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