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ELISA BASSOLI

Ricercatore t.d. art. 24 c. 3 lett. B
Dipartimento di Ingegneria "Enzo Ferrari"
Docente a contratto
Dipartimento di Ingegneria "Enzo Ferrari"

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Pubblicazioni

2024 - A computationally efficient procedure for calibrating model parameters of multiple specimens [Articolo su rivista]
Vincenzi, L.; Ponsi, F.; Bassoli, E.; Buratti, N.
abstract

2023 - A multi-temporal DInSAR-based method for the assessment of the 3D rigid motion of buildings and corresponding uncertainties [Articolo su rivista]
Bassoli, E.; Vincenzi, L.; Grassi, F.; Mancini, F.
abstract

2023 - Evaluation of TPMS Structures for the Design of High Performance Heat Exchangers [Relazione in Atti di Convegno]
Torri, F.; Berni, F.; Fontanesi, S.; Mantovani, S.; Giacalone, M.; Defanti, S.; Bassoli, E.; Colombini, G.
abstract

The development of the additive manufacturing tech nology has enabled the design of components with complex structures that were previously unfeasible with conventional techniques. Among them, the Triply Periodic Minimal Surface (TPMS) structures are gaining scientific interest in several applications. Thanks to their high surface-to-volume ratio, lightweight construction, and excep tional mechanical properties, TPMS structures are being investigated for the production of high-performance heat exchangers to be adopted in different industrial fields, such as automotive and aerospace. Another significant advantage of the TPMS structures is their high degree of design flexibility. Each structure is created by replicating a characteristic unit cell in the three spatial dimensions. The three key parameters, namely cell type, cell dimension and wall thickness can be adjusted to provide considerable versatility in the design process. As for the heat exchangers, the variation of these parameters results in different values of heat transfer and pressure drop. If, on the one and, this flexibility leads to a wide range of design possibilities, on the other hand it generates uncertainty when the most suitable cell (with the best set of parameters) has to be selected. Therefore, the aim of the paper is to address the initial challenge in the design process of an innovative heat exchanger that incorporates a TPMS structure, which is the selection of the unit cell. Based on a literature review, four TPMS structures are selected as the most promising ones for the purpose, namely Gyroid, I-WP, Primitive and Diamond. Small prototypes of the selected structures are numerically tested at laminar and turbulent flow conditions to compare their performances in terms of heat transfer and pressure drop against a more traditional solution. In order to ensure an unbiased comparison between the structures, they are compared on equal volume of the specimen, wall thickness and unit cell dimension. Finally, a compact plate heat exchanger based on turbulators is added to the comparison, to investigate the capabilities of the TPMS structures compared to a more conventional solution.

2023 - Mitigation of model error effects in neural network-based structural damage detection [Articolo su rivista]
Ponsi, F.; Bassoli, E.; Vincenzi, L.
abstract

This paper proposes a damage detection procedure based on neural networks that is able to account for the model error in the network training. Vibration-based damage detection procedures relied on machine learning techniques hold great promises for the identification of structural damage thanks to their efficiency even in presence of noise-corrupted data. However, it is rarely possible in the context of civil engineering to have large amount of data related to the damaged condition of a structure to train a neural network. Numerical models are then necessary to simulate damaged scenarios. However, even if a finite element model is accurately calibrated, experimental results and model predictions will never exactly match and their difference represents the model error. Being the neural network tested and trained with respect to the data generated from the numerical model, the model error can significantly compromise the effectiveness of the damage detection procedure. The paper presents a procedure aimed at mitigating the effect of model errors when using models associated to the neural network. The proposed procedure is applied to two case studies, namely a numerical case represented by a steel railway bridge and a real structure. The real case study is a steel braced frame widely adopted as a benchmark structure for structural health monitoring purposes. Although in the first case the procedure is carried out considering simulated data, we have taken into account some key aspects to make results representative of real applications, namely the stochastic modelling of measurement errors and the use of two different numerical models to account for the model error. Different networks are investigated that stand out for the preprocessing of the dynamic features given as input. Results show the importance of accounting for the model error in the network calibration to efficiently identify damage.

2023 - Size-scale effects and modelling issues of fibre-reinforced concrete beams [Articolo su rivista]
Cucuzza, R; Aloisio, A; Accornero, F; Marinelli, A; Bassoli, E; Marano, Gc
abstract

2022 - A simplified procedure to assess uncertainties in the estimation of the rigid motion of isolated buildings based on InSAR monitoring [Relazione in Atti di Convegno]
Bassoli, E; Grassi, F.; Eslami Varzaneh, G.; Ponsi, F.; Mancini, F.; Vincenzi, L.
abstract

2022 - Bayesian and deterministic surrogate-assisted approaches for model updating of historical masonry towers [Articolo su rivista]
Ponsi, F.; Vincenzi, L.; Bassoli, E.
abstract

2022 - Contribution of anthropogenic consolidation processes to subsidence phenomena from multi-temporal DInSAR: a GIS-based approach [Articolo su rivista]
Grassi, Francesca; Mancini, Francesco; Bassoli, Elisa; Vincenzi, Loris
abstract

The paper introduces an approach based on the combination of multi-temporal Differential Interferometric Synthetic Aperture Radar and geographical information systems analysis to investigate and separate several contributions to subsidence phenomena over the municipality of Ravenna (Emilia Romagna, Italy). In particular, the relationship between displacements detected over built environment and consolidation processes after construction was assessed and filtered out from the subsidence map to quantify the local overestimation of subsidence phenomena due to the mentioned processes. It requires descriptive attributes related to the age of construction and intended uses. The outcomes of the present study highlight ground consolidation processes that seem to be active over areas settled in the last 30 years with a component contributing to vertical rates up to 3 mm/yr. Such contribution represents the 20% of the cumulative displacements reported for coastal villages where different sources of subsidence increase the vulnerability to coastal erosion. We discuss the contribution of consolidation processes over a couple of recently settled areas to separate among contributions and avoid the misinterpretation of effects due to other anthropogenic sources of subsidence.

2022 - Impact of the model error on the neural network-based damage detection [Relazione in Atti di Convegno]
Ponsi, F.; Ghirelli, G.; Bassoli, E.; Vincenzi, L.
abstract

2022 - Surrogate-based bayesian model updating of a historical masonry tower [Relazione in Atti di Convegno]
Ponsi, F.; Bassoli, E.; Varzaneh, G. E.; Vincenzi, L.
abstract

This paper presents the surrogate-based Bayesian model updating of a historical masonry bell tower. The finite element model of the structure is updated on the basis of the modal properties experimentally identified thanks to a vibration test. In a general context, model updating results are highly affected by several uncertainties, regarding both the experimental measures and the model. Stochastic approaches to model updating, as the one based on Bayes' theorem, enable to quantify the uncertainties associated to the updated parameters and, consequently, to increase the reliability of the identification. The major drawback of Bayesian model updating is the high computational effort requested to compute the posterior distribution of parameters. For this reason, the paper proposes to integrate the classical procedure with a surrogate model. A Gaussian surrogate is employed for the approximation of the posterior distribution of parameters and the performances of the proposed method are compared to those of an Bayesian numerical method proposed in literature.

2021 - A multi-objective optimization approach for FE model updating based on a selection criterion of the preferred Pareto-optimal solution [Articolo su rivista]
Ponsi, F.; Bassoli, E.; Vincenzi, L.
abstract

Multi-objectives optimization problems are often solved constructing the Pareto front and applying a decision-making strategy to select the preferred solution among the Pareto-optimal solutions. With the aim to reduce the computational effort in multi-objective optimization problems, this paper presents a procedure for the direct evaluation of the preferred updated model, without the need to evaluate the whole Pareto front. For this purpose, the objective function to minimize is defined as the distance between a candidate point and the equilibrium point in the objective function space. The choice of the criterion of the minimum distance from the equilibrium point comes from a preliminary study carried out to assess the performances of different selection criteria. The robustness and the efficiency of the proposed procedure are assessed through the comparison with the results obtained from the estimation of the Pareto-optimal solutions and the subsequent selection of the preferred one for two numerical case studies. The proposed procedure is finally applied to the calibration of a complex FE model with respect to experimental modal data. Results show that the proposed procedure is effective and considerably reduces the computational effort. Moreover, the procedure is able to directly estimate the optimal weighting factor that allows to know the relative importance between the selected objectives and can be used to solve the multi-objective optimization with the weighed sum method.

2021 - A statistical approach for modeling individual vertical walking forces [Articolo su rivista]
Pancaldi, F.; Bassoli, E.; Milani, M.; Vincenzi, L.
abstract

This paper proposes a statistical approach for modeling vertical walking forces induced by single pedestrians. To account for the random nature of human walking, the individual vertical walking force is modeled as a series of steps and the gait parameters are assumed to vary at each step. Walking parameters are statistically calibrated with respect to the results of experimental tests performed with a force plate system. Results showed that the walking parameters change during walking and are correlated with each other. The force model proposed in this paper is a step-by-step model based on the description of the multivariate distribution of the walking features through a Gaussian Mixture model. The performance of the proposed model is compared to that of a simplified load model and of two force models proposed in the literature in a numerical case study. Results demonstrate the importance of an accurate modeling of both the single step force and the variability of the individual walking force.

2021 - Bayesian Model Updating and Parameter Uncertainty Analysis of a Damaged Fortress Through Dynamic Experimental Data [Relazione in Atti di Convegno]
Ponsi, Federico; Bassoli, Elisa; Vincenzi, Loris
abstract

A probabilistic analysis for the uncertainty evaluation of model parameters is of great relevance when dealing with structural damage assessment. Indeed, the identification of the damage severity associated to its uncertainty can support the decision-maker to close a bridge or a building for safety reasons. In this paper the results of the model updating of an historical masonry fortress damaged by the seismic event that hits the town of San Felice sul Panaro and the surrounding localities in the Po Valley in the 2012 are presented. A standard and a Bayesian updating procedures are first applied to the calibration of the complex Finite Element (FE) model of the fortress with respect to experimental modal data. The uncertainty of the identified parameters of structural system is then obtained by using the Bayesian probabilistic approach. The most probable parameter vector is obtained by maximizing the posterior probability density function. The robustness and the efficiency of the procedure are evaluated through the comparison with the results obtained from the estimation of the Pareto-optimal solutions.

2021 - Dynamic Identification and Model Updating of a Masonry Chimney [Relazione in Atti di Convegno]
Vincenzi, Loris; Bassoli, Elisa; Santoro, Valentino
abstract

The paper presents the results of tests performed on a historical masonry chimney and its damage evaluation. The studied masonry chimney exhibits a clear and well visible crack pattern. To evaluate the safety condition and to design rehabilitation interventions, an extensive non-destructive test campaign is performed. The paper describes the dynamic tests, the identification of the structural modal properties, the calibration of a structural Finite Element (FE) model based on the experimental results and the evaluation of the effect of cracks on its dynamic properties. Modal identification is performed using the so called covariance-driven Stochastic Subspace Identification method (SSI-COV) to estimate natural frequencies, mode shapes and modal damping ratios. Then, the model updating is performed to localize the damage starting from the identified modal properties. Instead of adjusting the stiffness properties for all the elements, a stiffness distribution is determined by means of damage patterns. The results of two damage patterns are compared with those of the undamaged model and with the visual inspection carried out on the structure.

2021 - Parameter Calibration of a Social Force Model for the Crowd-Induced Vibrations of Footbridges [Articolo su rivista]
Bassoli, E.; Vincenzi, L.
abstract

A reliable prediction of the human-induced vibrations of footbridges relies on an accurate representation of the pedestrian excitation for different loading scenario. Particularly, the modeling of crowd-induced dynamic loading is a critical issue for the serviceability assessment of footbridges. At the design stage, the modeling of crowd loading is often derived from single pedestrian models, neglecting the effect of the structural vibrations as well as the interactions among pedestrians. A detailed description of the crowd behavior can be achieved employing a social force model that describes the different influences affecting individual pedestrian motion. These models are widely adopted to describe the crowd behavior especially in the field of evacuation of public buildings, public safety and transport station management while applications in the serviceability assessment of footbridges are less common. To simulate unidirectional pedestrian flows on footbridges, this paper proposes a parameter calibration of the Helbing’s social force model performed adopting the response surface methodology. Parameters of the social force model are calibrated so as to represent the fundamental relation between mean walking speed and density of the pedestrian crowd. The crowd-induced vibrations are then simulated by modeling each pedestrian in the crowd as a vertical load that crosses the footbridge with time varying trajectory and velocity estimated from the calibrated social force model. Finally, results are compared to those obtained from a multiplication factor approach proposed in literature. This considers the crowd as a uniform distribution of pedestrians with constant speed and given synchronization level and the footbridge response is evaluated as the response to a single pedestrian scaled by a proper enhancement factor.

2019 - Dynamic Assessment of Masonry Towers Based on Terrestrial Radar Interferometer and Accelerometers [Articolo su rivista]
Castagnetti, Cristina; Bassoli, Elisa; Vincenzi, Loris; Mancini, Francesco
abstract

This paper discusses the performance of a terrestrial radar interferometer for the structural monitoring of ancient masonry towers. High-speed radar interferometry is an innovative and powerful remote sensing technique for the dynamic monitoring of large structures since it is contactless, non-destructive, and able to measure fast displacements on the order of tenths of millimeters. This methodology was tested on a masonry tower of great historical interest, the Saint Prospero bell tower (Northern Italy). To evaluate the quality of the results, data collected from the interferometer were compared and validated with those provided by two types of accelerometer-based measuring systems directly installed on the tower. Dynamic tests were conducted in operational conditions as well as during a bell concert. The first aimed at characterizing the dynamic behavior of the tower, while the second allowed to evaluate the bell swinging effects. Results showed a good agreement among the different measuring systems and demonstrated the potential of the radar interferometry for the dynamic monitoring of structures, with special focus on the need for an accurate design of the geometric aspects of the surveys.

2019 - Dynamic monitoring and evaluation of bell ringing effects for the structural assessment of a masonry bell tower [Articolo su rivista]
Vincenzi, L; Bassoli, E; Ponsi, Federico; Castagnetti, C; Mancini, F
abstract

The paper presents a rational procedure for the structural assessment of bell towers with respect to the dynamic actions induced by the bell ringing, based on structural monitoring and data processing. This methodology is tested on the bell tower of Saint Prospero (Reggio Emilia, Northern Italy), a masonry tower of great historical interest. The procedure includes an accurate geometrical survey for a deep knowledge of the structural geometry, which is the base for the structural modelling. A finite element model of the tower is calibrated with respect to the modal properties evaluated from the structural response measured in operational conditions. The structural response of the tower was also measured during a famous cultural event held in the city centre of Reggio Emilia, when skilled bell ringers played traditional melodies. The tower displacements are evaluated applying a double integration technique and a detrending procedure based on the empirical mode decomposition to the acquired accelerations. To simulate the structural response to the bell ringing, the tower and the bell are modelled as a single degree of freedom system and an unforced and undamped simple pendulum, respectively. For safety assessment purposes, the structural response of the tower is evaluated considering different oscillation angles in order to identify the one causing the maximum displacement. Finally, the stress pattern of the masonry caused by the bell-induced displacement is estimated thanks to the calibrated finite element model of the tower. Results show that the bell ringing causes a stress pattern lower than the allowable masonry strength for the serviceability conditions.

2019 - Monitoraggio di strutture storiche mediante interferometria radar terrestre [Relazione in Atti di Convegno]
Bassoli, Elisa; Ponsi, Federico; Castagnetti, Cristina; Mancini, Francesco; Vincenzi, Loris
abstract

In questa memoria vengono discusse le prestazioni, i vantaggi e gli svantaggi dell’interferometria radar terrestre con antenna ad apertura reale (TInRAR) per il monitoraggio strutturale degli edifici esistenti e storici. L’interferometro radar terrestre è in grado di rilevare spostamenti differenziali confrontando la fase del segnale radar raccolto e riflesso dalla struttura rispetto a quella del segnale trasmesso. Gli spostamenti lungo la linea di vista (LoS) che si possono misurare sono dell’ordine del centesimo di millimetro e le misure possono essere campionate con frequenza fino a 200 Hz. La memoria riporta i test dinamici effettuati sulla torre campanaria della Basilica di San Prospero a Reggio Emilia (Italia), confrontando gli spostamenti misurati dal radar terrestre con i valori ottenuti per doppia integrazione delle accelerazioni misurate da accelerometri installati direttamente sulla struttura. Grazie alla capacità di misurare in maniera continua e diretta gli spostamenti di numerosi punti della struttura, l’uso della strumentazione TInRAR integrata alla strumentazione tradizionale potrebbe essere di grande ausilio nell’interpretazione del comportamento strutturale e nella valutazione della progressione di un potenziale danneggiamento nelle strutture a seguito di eventi sismici.

2019 - Ottimizzazione multi-obiettivo di modelli a elementi finiti: criteri per la scelta della soluzione ottimale [Relazione in Atti di Convegno]
Ponsi, Federico; Bassoli, Elisa; Vincenzi, Loris
abstract

La possibilità di avere modelli ad elementi finiti accurati riveste una grande importanza nella valutazione degli effetti di un evento sismico sulla struttura e nell’identificazione di eventuali danni. Per migliorare l’accuratezza del modello numerico è possibile utilizzare tecniche di model updating per calibrare parametri fisici/strutturali del modello sulla base dei dati misurati sulla struttura reale da un sistema di monitoraggio. La maggior parte dei problemi di calibrazione di modelli di strutture reali presenta diversi obiettivi che sono generalmente in conflitto tra loro. Un approccio comune per risolvere l’ottimizzazione multi-obiettivo è quello di minimizzare una funzione a singolo obiettivo definita come la combinazione pesata dei diversi obiettivi. L’articolo presenta l’effetto sui parametri fisici/strutturali calibrati del fattore peso che governa la funzione obiettivo nel metodo della somma ponderata. Dopo aver valutato la frontiera di Pareto, ripetendo la procedura di ottimizzazione più volte per diversi valori del fattore peso, la memoria descrive e confronta i risultati ottenuti da diversi criteri per trovare la soluzione ideale tra quelle ottime che formano la frontiera di Pareto, con lo scopo di ottenere la soluzione che rappresenta quindi il miglior compromesso tra gli obiettivi diversi. Viene proposta quindi una procedura in grado di ottenere la soluzione ideale senza la necessità di calcolare l’intera frontiera di Pareto, consentendo un notevole risparmio di tempo nell’intero processo. La procedura proposta è presentata attraverso il caso studio della Rocca di San Felice sul Panaro, gravemente danneggiata durante gli eventi sismici dell’Emilia nel 2012.

2018 - A spectral load model for pedestrian excitation including vertical human-structure interaction [Articolo su rivista]
Bassoli, Elisa; Van Nimmen, Katrien; Vincenzi, Loris; Van den Broeck, Peter
abstract

This paper is focused on the evaluation of the structural response to vertical pedestrian excitation for a wide range of footbridge and crowd parameters. A spectral load model for pedestrian-induced forces proposed in literature is adopted. The model accounts for the randomness in the human excitation as well as the increased correlation among pedestrians with pedestrian density. Therefore, it can be applied for the vibration serviceability analysis of footbridges in unrestricted and crowded traffic conditions. With the purpose of predicting the structural response for a wide range of natural frequencies, an extension of the model to account for the contribution of the first three harmonics of the walking load is proposed. To allow for a more accurate prediction of the maximum response, the present study in addition accounts for the vertical mechanical interaction between pedestrians and the supporting structure. Finally, the impact of human-structure interaction (HSI) on the structural response is investigated. By applying the methods of linear random dynamics, the maximum dynamic response of the footbridge is evaluated based on an analytical formulation of the load and the frequency response function (FRF) of the coupled crowd-structure system. The most significant HSI-effect is in the increase of the effective damping ratio of the coupled crowd-structure system that leads to a reduction of the structural response. However, in some cases the shift in frequency of the coupled crowd-structure system results into a higher structural response when HSI-effects are accounted for.

2018 - Ambient vibration-based finite element model updating of an earthquake-damaged masonry tower [Articolo su rivista]
Bassoli, Elisa; Vincenzi, Loris; D'Altri, Antonio Maria; de Miranda, Stefano; Forghieri, Marianna; Castellazzi, Giovanni
abstract

This paper presents a vibration-based model updating procedure for historical masonry structures which have suffered severe damage due to seismic events. This allows gathering in-depth insights on the current condition of damaged buildings, which can be beneficial for the knowledge of their actual structural behaviour and, consequently, for the design of repairing and strengthening interventions. The methodology, based on the experimentally identified modal parameters, is tested on the San Felice sul Panaro medieval fortress, which was heavily damaged by the 2012 Emilia earthquake. The finite element mesh of the structure in its post-quake condition is generated by means of a nonstandard semi-automatic mesh generation procedure based on a laser scanner points cloud. Ambient vibration testing is performed on the main tower of the fortress. Mechanical properties of the tower and the level of connections with the rest of the fortress in its current damaged state are investigated. To fully characterize the actual behaviour of the tower in operational condition, mesh elements corresponding to the damaged masonry are identified and different material properties are assigned to them. This allows to account for the effect of damage and cracks, which appeared essential in the calibration process. The updating procedure is carried out by means of an advanced surrogate-assisted evolutionary algorithm designed for reducing the computational effort.

2018 - Human-induced vibrations of a curved cable-stayed footbridge [Articolo su rivista]
Bassoli, Elisa; Gambarelli, Paola; Vincenzi, Loris
abstract

This paper investigates and compares the performances of two simulation models to predict the footbridge response to vertical pedestrian dynamic actions. For this purpose, a rational procedure based on experimental tests, identification, model-updating and simulation is addressed. The object of study is the Pasternak footbridge, a curved cable-stayed footbridge prone to human-induced vibrations. The footbridge dynamic behaviour is investigated thanks to an experimental campaign. Accelerations due to ambient vibrations are recorded and the modal parameters of the structure are identified. The dynamic response to pedestrian actions is investigated performing several experimental tests with different-sized groups of pedestrians. To simulate the dynamic response to pedestrian actions, a Finite Element (FE) model of the footbridge is developed and calibrated so that the numerical dynamic properties match the experimental ones. The structural response to human loads is evaluated through two advanced simulation methods. The first one is based on a periodic walking force and is employed to perform dynamic analyses with the FE model. In the second one, a multi-harmonic force model, which considers the variability of the walking force, is adopted and the dynamic response is evaluated via modal decomposition. Finally, numerical and experimental results are compared with each other.

2017 - Dynamic behaviour of the San Felice sul Panaro Fortress: Experimental tests and model updating [Relazione in Atti di Convegno]
Forghieri, Marianna; Bassoli, Elisa; Vincenzi, Loris
abstract

This paper describes the experimental tests and numerical analyses performed to characterize the dynamic behaviour of the principal tower of the San Felice sul Panaro Fortress (Modena, Italy). After the Emilia earthquake that occurred in 2012, the Fortress reported serious damage, such as severe cracks on the walls and collapses of several towers and the roof. As a part of a research that aims at evaluating the vulnerability of the Fortress and designing retrofitting interventions, full-scale ambient vibration tests were performed to evaluate the dynamic properties of the principal tower. Afterwards, a Finite Element (FE) model is calibrated to obtain a good match between the numerical and experimental modal properties. The optimization process is carried out through an improved surrogate-assisted evolutionary strategy. Due to the serious damage of the Fortress, the effective stiffness of the cracked masonry and the efficiency of connection at the interface between the principal tower and the rest of the Fortress are considered the main uncertain quantities to be calibrated. A multi-objective optimization is performed, considering the frequency and mode shape residuals. These are defined as the difference between experimental and numerical modal properties. The multi-objective optimization is reduced to a series of a single-objective optimization adopting the weighted sum method. The set of optimal solutions that form the Pareto front is obtained performing the optimization for different values of the weighting factors. Then, two criteria are used and compared in order to find the preferred solution among the Pareto front solutions. Finally, a comparison of the identified structural parameters obtained varying the weighting factors for natural frequencies and mode shapes in the optimization process is presented, highlighting the importance of a proper choice of the weighting factors.

2017 - Identificazione della rigidezza dei tamponamenti in strutture intelaiate mediante analisi inversa [Relazione in Atti di Convegno]
Tondi, Michele; Bovo, Marco; Bassoli, Elisa; Vincenzi, Loris; Savoia, Marco
abstract

È ben noto ormai che i tamponamenti, per azioni sismiche corrispondenti a Stati Limite di Operatività o di Danno, giocano un ruolo spesso determinante nel comportamento dinamico di strutture intelaiate, sia in calcestruzzo armato che in acciaio, soprattutto quando introducono significative irregolarità in pianta o in altezza. I tamponamenti possono essere introdotti nella modellazione mediante elementi di rigidezza equivalente, ad esempio bielle, al fine di valutare l’effettiva rigidezza della struttura. Nonostante in letteratura siano proposte diverse formulazioni basate su prove di laboratorio, le condizioni di posa e di realizzazione delle tamponature possono influire sulla effettiva rigidezza del sistema telaio-tamponamento, soprattutto quando si valuta il comportamento di edifici esistenti per i quali le incertezze sono più significative. Questo studio presenta una procedura per la valutazione della rigidezza effettiva dei tamponamenti mediante l’identificazione sperimentale delle caratteristiche modali dell’edificio, la definizione di opportuni modelli meccanici per struttura e tamponamenti e l’utilizzo di un avanzato algoritmo evolutivo per calibrare la rigidezza del tamponamento sulla base delle quantità sperimentali identificate. Nella memoria vengono presentati i risultati delle analisi condotte su telai multipiano al fine di indagare la variabilità dei risultati ottenuti in funzione dell’incertezza dei parametri modali della struttura.

2017 - Structural health monitoring of a historical masonry bell tower using operational modal analysis [Relazione in Atti di Convegno]
Bassoli, Elisa; Forghieri, Marianna; Vincenzi, Loris; Bovo, Marco; Mazzotti, Claudio
abstract

This paper addresses the modal and structural identification of the historical masonry bell tower of Ficarolo, in Italy. After the seismic sequence of May 2012, the tower reported a serious damage pattern. Retrofitting interventions were designed and they mainly consisted in the rebuilding of cracked zones and the strengthening of masonry walls with carbon bars embedded in the masonry with epoxy resin. Afterwards, a continuous dynamic monitoring system has been installed on the tower. From the recorded structural response under ambient excitation, the dynamic characteristics of the tower are identified using Operational Modal Analysis techniques. Results of the first months of continuous monitoring are presented in this paper. Moreover, in order to analyse the evolution of the structural behaviour, the effect of changing temperature on the identified natural frequencies is investigated. The experimental modal parameters are also used to identify the elastic modulus of the reinforced masonry through the calibration of a Finite Element (FE) model of the tower. In addition, the influence of the soil-foundation system on the structural behaviour is evaluated. The calibration procedure is performed adopting an improved surrogate-assisted evolutionary strategy. The calibrated FE model can be adopted to simulate the structural response to far-field earthquakes. Moreover, the monitoring system can give valuable information on the structural behaviour and the structural health in the case of seismic events.

2017 - The role of environmental effects in the structural health monitoring: the case study of the Ficarolo Tower in Rovigo, Italy [Relazione in Atti di Convegno]
Bassoli, Elisa; Forghieri, Marianna; Bovo, Marco; Mazzotti, Claudio; Vincenzi, Loris
abstract

The paper presents some preliminary results of the dynamic monitoring of the Ficarolo Tower. The Ficarolo Tower is an historical masonry bell tower about 68 m high and characterized by impressive inclination. The tower reported serious damage during the seismic sequence of May 2012 and, consequently, retrofitting interventions were carried out and a continuous dynamic monitoring system was installed. Valuable information on the structural behaviour and the structural health in the case of seismic events can be obtained from the monitoring system. Modal-based damage detection procedure are based on the relation between variations in the measured modal parameters and changes in the physical properties, such as stiffness reductions due to damage. However, important variations in the dynamic response of a healthy structure can also be caused by changing in the environmental conditions, leading to a false positive diagnosis. For a proper modal-based damage detection, the effects of temperature and humidity on the modal properties have to be removed. To this aim, the paper investigates the effects of temperature and humidity variations on the identified natural frequencies.

2016 - Human-structure interaction effects on the maximum dynamic response based on an equivalent spectral model for pedestrian-induced loading [Relazione in Atti di Convegno]
Bassoli, Elisa; Van Nimmen, Katrien; Vincenzi, Loris; Van den Broeck, Peter
abstract

The paper investigates the effects of the human-structure interaction (HSI) on the dynamic response based on a spectral model for vertical pedestrian-induced forces. The spectral load model proposed in literature can be applied for the vibration serviceability analysis of footbridges subjected to unrestricted pedestrian traffic as well as in crowded conditions, however, in absence of HSI phenomena. To allow for a more accurate prediction of the maximum structural response, the present study in addition accounts for the vertical mechanical interaction between pedestrians, represented by simple lumped parameter models, and the supporting structure. By applying the classic methods of linear random dynamics, the maximum dynamic response is evaluated based on the analytical expression of the spectral model of the loading and the frequency response function (FRF) of the coupled system. The most significant HSI-effect is in the increase of the effective damping ratio of the coupled system that leads to a reduction of the structural response. However, in some cases the effect of the change in the frequency of the coupled system is more significant, whereby this results into a higher structural response when the HSI-effects are accounted for.

2015 - Dynamic analyses of a curved cable-stayed footbridge under human induced vibrations: numerical models and experimental tests [Relazione in Atti di Convegno]
Bassoli, Elisa; Gambarelli, Paola; Simonini, Laura; Vincenzi, Loris
abstract

Nowadays, pedestrian bridges are increasingly lively and slender structures due to the devel-opment of improved structural materials and aesthetic requirements. As a result of this trend, contemporary footbridges are more and more prone to human-induced vertical and lateral vibrations that can compromise the comfort serviceability conditions. The goal of this paper is to characterize the dynamic behaviour of a curved cable-stayed footbridge subjected to pedestrian loads starting from experimental tests and numerical dynamic analyses. The dynamic behaviour of the footbridge is investigated thanks to an experimental campaign per-formed by means of an advanced MEMS-based SHM system. Accelerations due to ambient vibrations are recorded and the modal parameters of the structure are identified by means of a classic identification method. Then, to investigate the dynamic response of the footbridge subjected to pedestrian actions, a wide number of experimental tests were performed with dif-ferent-sized groups of pedestrians crossing the footbridge, running, free or synchronized walking with different pacing frequencies. Then, a finite element model of the footbridge is developed and calibrated so that the numerical dynamic predictions agree with the experi-mental modal properties. Then, to simulate dynamic loading conditions due to a single pedes-trian or a crowd of people crossing the footbridge, two mathematical models are examined. In the first approach both the non-calibrated and the updated FE model are adopted to evaluate the vertical dynamic response of the footbridge when subjected to pedestrian loads. Dynamic analyses are performed by simulating the pedestrian walking through a periodic load model representing the human-induced force as a deterministic force. The second approach is based on the solution of the equation of motion via modal decomposition, considering multi-harmonic forces and experimental mode shapes and frequencies. Finally, the accelerations obtained through the mathematical approaches are compared with the experimental results.

2015 - Dynamic identification of an ancient masonry bell tower using a MEMS-based acquisition system [Relazione in Atti di Convegno]
Bassoli, Elisa; Vincenzi, Loris; Bovo, Marco; Mazzotti, Claudio
abstract

In this paper results of dynamic tests performed on a bell tower located in Ficarolo (Italy) are reported. After the Emilia earthquake that occurred in 2012, the bell tower reported a serious damage pattern and, as a consequence, retrofitting interventions were carried out. Dynamic tests before and after the strengthening were performed to investigate the modal properties of the bell tower and to evaluate possible changes in dynamic behavior due to the intervention. Accelerations during ambient vibrations were recorded by means of an advanced MEMS-based system, whose main features are the transmission of the data in digital form and the possibility of performing some system analyses directly on-board of the sensors. Accelerations were acquired using 11 biaxial MEMS units. First 8 modes are clearly identified, with natural frequencies in the range 0.5-9.0 Hz. Finally, a comparison between the performances of the installed MEMS-based system and a traditional analog (piezoelectric) system is carried out and results are critically compared.

2015 - Dynamic monitoring of the Pasternak footbridge using MEMS-based sensing system [Relazione in Atti di Convegno]
Bassoli, Elisa; Gambarelli, Paola; Simonini, Laura; Vincenzi, Loris; Savoia, Marco
abstract

The aim of this paper is to investigate the dynamic behaviour of a steel curved cable-stayed footbridge using an advanced MEMS-based Structural Health Monitoring system. Experimental campaigns were carried out in July and December to characterize the dynamic behaviour of the footbridge subjected to ambient vibrations and human-induced loading actions and to evaluate the effects of temperature shifts on structural modal properties. The monitoring system is composed of a controller and storage unit and several intelligent bus-connected sensing units that can record both the accelerations along two orthogonal axes and the temperature. The main features of this system are the transmission of data in digital form and its high signal-to-noise ratio in the low and medium-low frequency range. The structural dynamic properties are identified through the classic Enhanced Frequency Domain Decomposition (EFDD) method that is based on the diagonalization of the spectral density matrix. A preliminary FE model of the footbridge is built and the numerical results are compared with the experimental ones.

2013 - Dynamic Behaviour of a steel footbridge under pedestrian loads [Relazione in Atti di Convegno]
Vincenzi, L.; Bassoli, E; Gambarelli, P.
abstract

Footbridges are generally effective structures concerning the static behavior, since they are subjected to a limited level of live loads. Nevertheless, the frequency range of the pedestrian dynamic actions may fall within the natural frequency interval of the structure, giving high dynamic amplifications. Therefore, dynamic properties of footbridges and effects of pedestrian loads need to be analyzed, comparing experimental and numerical results. This paper is part of a research that aims to characterize the dynamic behavior of a steel footbridge with reference to pedestrian dynamic amplifications. The structure, located in Reggio Emilia (Italy), is about 170 meters long and composed of 5 simple-supported spans, linked at lower-floor level. To investigate the dynamic behavior of the footbridge, an experi-mental campaign has been first performed. Accelerations due to ambient vibrations (wind) and to pedestrian dynamic actions were recorded. In particular, a wide number of pedestrian dynamic loading conditions have been considered, such as excitations induced by people jumping, running and walking with different passing frequencies. Accelerations were acquired by an advanced MEMS-based system. 10 biaxial MEMS sensors were arranged in 3 different setups in order to identify as many natural modes as possible and to investigate the vibration level in several components of the footbridge. The post-processing of experimental data allows to determine both the dynamic properties of the structure (frequencies, mode shapes and damping ratios) and the maximum accelerations caused by pedestrian actions. The dynamic characteristics are identified by means of the classic Enhanced Frequency Domain Decomposition (EFDD) method that is based on the diago-nalization of the spectral density matrix. Then, a finite element model is built and calibrated such that the analytical dynamic predictions agree with the experimental modal properties. Finally, the measured accelerations caused by pedestrian dynamic actions are compared with those given by the numerical model, con-sidering different dynamic load models.

2013 - Identification of the Manhattan bridge dynamic properties for fatigue assessment [Relazione in Atti di Convegno]
Savoia, M.; Vincenzi, Loris; Bassoli, E.; Gambarelli, P.; Betti, R.; Testa, R.
abstract

In this paper, dynamic properties and results of the identification process on the Manhattan Bridge are described. Accelerations during ambient vibrations have been recorded using an advanced MEMSbased system,whose main features are the transmission of the data in digital formand the possibility of performing some system analyses directly on-board of the sensors, transmitting synthetic data only to the main computer. 28 MEMS accelerometers have been used and 4 different experimental setups adopted. Several modes of the main span are identified, with natural frequencies in the range 0.2-1.0 Hz. A FE model updating procedure is also performed by means of an improved Evolutionary Algorithm. After the updating procedure, numerical modal frequencies and mode shapes match well the experimental data. This work is part of a research that aims at investigating how real-time monitoring systems can be used to detect the occurrence of fatigue phenomena induced by vibrations and distortion modes in existing steel bridges.

2013 - Monitoraggio e identificazione dinamica del “Manhattan Bridge” di New York [Relazione in Atti di Convegno]
Bassoli, E; Gambarelli, P.; Vincenzi, L.; Savoia, M.
abstract

In this paper, dynamic proprieties and results of the identification process on the Manhattan Bridge are described. Accelerations caused by ambient vibrations are recorded using an advanced MEMS-based system, whose main features are the transmission of the data in digital form and the possibility of performing some system analyses directly on-board of the sensors, transmitting synthetic data only to the main computer. 28 MEMS accelerometers are used and 4 different experimental setups are adopted in order to identify a significant number of modes of the bridge. A standard frequency domain identification technique is applied (the Enhanced Frequency Domain Decomposition -EFDD) and the dynamic properties of the bridge (such as natural frequencies, mode shapes and damping ratios) are obtained. Several modes of the main span are identified, with natural frequencies in the range 0.2-1.0 Hz. A Finite Element model is then built and a model updating procedure is also performed using an improved Evolutionary Algorithm is used. After the updating procedure, the numerical modal frequencies and mode shapes match well the experimental ones. This work is part of a research that aims to investigate how real-time monitoring systems can be used to detect damages induced by vibrations and distortions in existing steel bridges.