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Loris VINCENZI

Professore Associato
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 - Efficient two-step procedure for parameter identification and uncertainty assessment in model updating problems [Articolo su rivista]
Tondi, M.; Bovo, M.; Vincenzi, L.
abstract

The model updating procedures employed in vibration-based health monitoring need to be reliable and computationally efficient. The computational time is a fundamental task if the results are used to evaluate, in quasi-real-time, the safe or the unsafe state of strategic and relevant structures. The paper presents an efficient two-step procedure for the identification of the mechanical parameters and for the assessment of the corresponding uncertainty in model updating problems. The first step solves a least squares problem, providing a first estimate of the unknown parameters. The second (iterative) step produces a refinement of the solution. Moreover, by exploiting the error propagation theory, this article presents a direct (non-iterative) procedure to assess the uncertainty affecting the unknown parameters starting from the experimental data covariance matrix. To test the reliability of the procedure as well as to prove its applicability to structural problems, the methodology has been applied to two test-bed case studies. Finally, the procedure has been used for the damage assessment in an existing building. The results provided in this article indicate that the procedure can accurately identify the unknown parameters and properly localize and quantify the damage.

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 - Novel Movement-Based Methods for the Calibration of Colocated Multiple-Input Multiple-Output Radars [Articolo su rivista]
Guerzoni, G.; Faghand, E.; Vitetta, G. M.; Vincenzi, L.; Mehrshahi, E.
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 - A proper infill sampling strategy for improving the speed performance of a Surrogate-Assisted Evolutionary Algorithm [Articolo su rivista]
Vincenzi, Loris; Gambarelli, Paola
abstract

In the present paper, an improved Surrogate-Assisted Evolutionary Algorithm is proposed. It combines the Differential Evolution algorithm with a quadratic surrogate approximation and a proper infill sampling strategy to choose appropriate sample points. The selection of the new candidate points is arranged to enhance both the local accuracy and the global optimum search. A comparison between performances of different evolutionary algorithms is carried out by searching the global minimum of two benchmark functions, by solving a dynamic identification problem of a three floor frame and by calibrating the non-linear stress-crack opening relation for Fibre-Reinforced Concrete specimens starting from experimental data.

2017 - Damage and collapses in industrial precast buildings after the 2012 Emilia earthquake [Articolo su rivista]
Savoia, Marco; Buratti, Nicola; Vincenzi, Loris
abstract

The present paper presents a complete and commented collection of cases of damage and collapse in reinforced concrete (RC) precast industrial buildings, observed by the authors during a series of field surveys after the 2012 Emilia earthquake in Northern Italy. They were selected among a total of about 2000 industrial RC precast buildings, whose structural characteristics and damage have been collected in a large database by the authors. The main causes of the collapses were vulnerabilities related to the structural characteristics of Italian precast buildings not designed with seismic criteria. In particular, these structures were typically built as an assembly of monolithic elements (roof elements, main and secondary beams, columns) in statically determinate configurations. The most common failure causes identified were: the absence of mechanical connectors between precast monolithic elements, the interaction of structural elements with non-structural walls, the insufficient column bending capacity, the rotation of pocket foundations, the inadequacy of connections of external precast cladding walls to bearing elements (columns and beams), the overturning of racks in buildings used as warehouses or in automated storage facilities.

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 - Influence of model errors in optimal sensor placement [Articolo su rivista]
Vincenzi, Loris; Simonini, Laura
abstract

The paper investigates the role of model errors and parametric uncertainties in optimal or near optimal sensor placements for structural health monitoring (SHM) and modal testing. The near optimal set of measurement locations is obtained by the Information Entropy theory; the results of placement process considerably depend on the so-called covariance matrix of prediction error as well as on the definition of the correlation function. A constant and an exponential correlation function depending on the distance between sensors are firstly assumed; then a proposal depending on both distance and modal vectors is presented. With reference to a simple case-study, the effect of model uncertainties on results is described and the reliability and the robustness of the proposed correlation function in the case of model errors are tested with reference to 2D and 3D benchmark case studies. A measure of the quality of the obtained sensor configuration is considered through the use of independent assessment criteria. In conclusion, the results obtained by applying the proposed procedure on a real 5-spans steel footbridge are described. The proposed method also allows to better estimate higher modes when the number of sensors is greater than the number of modes of interest. In addition, the results show a smaller variation in the sensor position when uncertainties occur.

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 - AR+ noise versus AR and ARMA models in SHM-oriented identification [Relazione in Atti di Convegno]
Guidorzi, Roberto; Diversi, Roberto; Vincenzi, Loris; Simioli, Vittorio
abstract

The most common approach in Structural Health Monitoring (SHM) consists in performing accelerometric measures of the response of the monitored structures to natural or artificial stimuli (e.g. wind, urban traffic, seismic events etc.) and in modeling the dynamic behavior of the structure on the basis of these measures. The models can be used, in particular, to extract and compare the main modes i.e. the main resonant frequencies and in comparing these frequencies with those concerning the initial state of integrity of the building. This paper compares the results given by traditional AR and ARMA models with those offered by AR+noise models where an additive observation error is considered and shows that these models can offer some advantages in SHM applications in that describe more accurately the stochastic context of the process. The comparisons have been performed on two different sets of data: the first one has been collected on an industrial building in occasion of an heavy seismic event whereas the second one has been collected on a medieval tower excited by urban traffic.

2015 - Coupling Response Surface and Differential Evolution for Parameter Identification Problems [Articolo su rivista]
Vincenzi, Loris; Savoia, Marco
abstract

In the present article, a new surrogate-assisted evolutionary algorithm for dynamic identification problems with unknown parameters is presented. It is based on the combination of the response surface (RS) approach (the surrogate model) with differential evolution algorithm for global search. Differential evolution (DE) is an evolutionary algorithm where N different vectors collecting the parameters of the system are chosen randomly or by adding weighted differences between vectors obtained from two populations. In the proposed algorithm (called DE-Q), the RS is introduced in the mutation operation. The new parameter vector is defined as the one minimizing the second-order polynomial function (RS), approximating the objective function. The performances in terms of speed rate are improved by introducing the second-order approximation; nevertheless, robustness of DE algorithm for global minimum search of objective function is preserved, because multiple search points are used simultaneously. Numerical examples are presented, concerning: search of the global minimum of analytical benchmark functions; parameter identification of a damaged beam; parameter identification of mechanical properties (masses and member stiffnesses) of a truss-girder steel bridge starting from frequencies and eigenvectors obtained from an experimental field test.

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.

2015 - Influence of measurement and model errors in optimal sensor placement for SHM purposes [Relazione in Atti di Convegno]
Simonini, Laura; Vincenzi, Loris
abstract

In this work, the influence of measurement and model errors in optimal sensor placement is investigated. The sensor placement procedure is based on the Information Entropy theory and the solution of the optimization problem is obtained maximizing the determinant of the so called Fisher Information Matrix (FIM). Results of placement process considerably depend on the so called covariance matrix of prediction error as well as on the definition of the correlation function. The paper thus investigates the role of the covariance matrix and the correlation function in optimal sensor placement. Different proposals on their definition are compared. A constant and an exponential correlation function depending on the distance between sensors are firstly assumed; then a new proposal depending from both the distance and modal vectors is presented. The method is finally applied to a benchmark case study and the effect of model and measurement error on results is described.

2014 - A surrogate-assisted evolutionary algorithm for dynamic structural identification [Relazione in Atti di Convegno]
Gambarelli, Paola; Vincenzi, Loris
abstract

In the present paper, the performances of surrogate-assisted evolutionary algorithms for dynamic identification problems and damage detection are investigated. An improved algorithm is designed to limit the computational effort by introducing a proper infill sampling strategy in Differential Evolution (DE). The algorithm combines the robustness of DE with the computational efficiency due to a second-order surrogate approximation of the objective function. New individuals are selected trying to enhance both the accuracy in the region of the optimum predicted by the surrogate and the global exploration. The efficiency of the algorithm is tested by searching the global minimum of benchmark functions and by solving damage identifi-cation problems. Results are compared with those obtained adopting both the original DE algorithm and a previous proposal surrogate-based algorithm called DE-Q.

2014 - Structural monitoring of a tower by means of MEMS–based sensing and enhanced autoregressive models [Articolo su rivista]
Guidorzi, Roberto; Diversi, Roberto; Vincenzi, Loris; Mazzotti, Claudio; Simioli, Vittorio
abstract

Structural Health Monitoring (SHM) methodologies are taking advantage of the development of new families of MEMS sensors and of the available network technologies. Advanced systems rely on intelligent bus-connected sensing units performing locally data filtering, elaboration and model identification. This paper describes a family of enhanced multivariate autoregressive models that can be used in SHM-oriented identification procedures and the implementation of a new advanced SHM system in the tower of the Engineering School of Bologna University. It describes also the results given by the considered procedure and a comparison of the implemented MEMS-based system with a traditional solution based on piezoelectric seismic accelerometers.

2013 - A new denoising procedure based on empirical mode decomposition for SHM purpose [Relazione in Atti di Convegno]
Mukhopadhyay, S.; Betti, R.; Galli, E.; Savoia, M.; Vincenzi, Loris
abstract

In this work, a signal processing method based on the Empirical Mode Decomposition (EMD) to denoise a recorded signal is proposed. EMD expresses the signal as an expansion of basis functions (Intrinsic Mode Functions - IMFs) that are signal dependent and are estimated via an iterative procedure.The decomposition of an "only noise" signal is first studied to define a Noise-Model in terms of energy and period. Then, the EMD is applied to a simulated measured signal, and the IMFs obtained are compared with the Noise-Model constructed before. Finally, an optimization procedure is performed to split the IMFs of the measured signal into 2 components: The denoised IMFs and the corresponding "Removed Noise" IMFs. The denoised IMFs are finally summed in order to reconstruct the denoised signal. The proposed algorithm is applied to a simple 3-floor shear-type frame and the ASCE 4-floor frame benchmark. The results are compared with those obtained by a standard denoising procedure based on a pass-band filter; the comparison confirmed the improvements obtained with the proposed method over classical procedures.

2013 - Comparison between Coupled Local Minimizers method and Differential Evolution algorithm in dynamic damage detection problems [Articolo su rivista]
Vincenzi, Loris; De Roeck, G.; Savoia, M.
abstract

In the present paper, a comparison is made between the Coupled Local Minimizers (CLM) method and the Differential Evolution (DE) algorithm to perform FE model updating for the damage detection in a cracked beam. CLM method is a gradient-based method with multiple local optimization runs. DE algorithm is a direct search approach which uses a population of solution vectors collecting the design parameters. Two benchmark examples of damage assessment are considered, i.e., beams under flexural vibrations with one crack and two cracks, with unknown position and depth. The effectiveness of the two methods to obtain the set of unknown parameters has been verified by performing a number of optimization processes starting from initial values of parameters selected randomly. Both exact and pseudo-experimental input data are used. A statistical analysis of the optimization results is presented. Both methods give results much better than the classical gradient optimization method. Better performances in term of speed rate and precision have been obtained by CLM when the number of identified parameters is limited. On the other hand, DE shows good efficiency when the number of parameters increases or in the case of pseudo-experimental input data.

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.

2012 - Damages and collapses in industrial precast buildings after the Emilia earthquake [Articolo su rivista]
Savoia, M; Mazzotti, C.; Buratti, N.; Ferracuti, B.; Bovo, M.; Ligabue, V.; Vincenzi, Loris
abstract

The present paper describes the collapses in precast industrial buildings caused by the 2012 Emilia earthquake. This kind of buildings, not designed with seismic criteria, has been found very vulnerable for several reasons, such as the absence of connecting systems between the various precast monolithic elements, the inadequacy of connection systems of external precast walls to the bearing elements (columns and beams), the interaction between non-structural walls and structural elements, and the inadequacy of the foundations.

2012 - Evaluation of a MEMS--based sensing unit for structural health monitoring: results on a medieval tower [Relazione in Atti di Convegno]
Guidorzi, Roberto; Diversi, Roberto; Vincenzi, Loris; Simioli, Vittorio
abstract

Structural health monitoring is a field that relies on different methodologies to develop procedures that characterize the dynamic properties of physical structures to identify possible deteriorations of their behaviors. SHM systems include usually a data acquisition subsystem suitable for recording the structure response to ambient or external excitations. The recorded data are then analyzed in order to characterize the dynamic properties of the considered structure. This paper describes some tests performed by means of a new advanced SHM system, the Teleco SHM602, on a truncated middle-age tower presently included in an ancient palace of the XVI century located in the central part of Bologna. These tests rely on models obtained by means of standard and advanced identification techniques

2012 - Experimental analysis and fatigue assessment on a railway steel viaduct [Relazione in Atti di Convegno]
Vincenzi, Loris; Savoia, M. Salvatore W.
abstract

the preliminary results concerning the fatigue assessment of Lagoscuro railway viaduct are described. Experimental dynamic tests have been performed in order to identify the modal properties of the bridge. Then, a FE model is corrected with a model updating procedures, where the uncertain model properties are adjusted in order to have the numerical predictions as close as possible to the measured data. Making use of the FE model, a preliminary fatigue assessment is carried out following the procedure defined in EN1993.

2012 - Experimental modal analysis and fatigue assessment on the Lagoscuro viaduct. [Relazione in Atti di Convegno]
Vincenzi, Loris; Savoia, M.; Salvatore, W.
abstract

In this paper, the preliminary results concerning the fatigue assessment of Lagoscuro railway viaduct is described. First, experimental dynamic tests have been performed in order to identify the modal properties. Then, a FE model is corrected with a model updating procedures, where the uncertain model properties are adjusted in order to have the numerical predictions as close as possible to the measured data. Making use of the FE model, a preliminary fatigue assessment is carried out following the procedure defined in EN1993.

2012 - Terremoto dell’Emilia - danni ad edifici produttivi a struttura prefabbricata ((Emilia earthquake - damage to buildings in manufacturing prefabricated structure)) [Articolo su rivista]
Savoia, M; Mazzotti, C.; Buratti, N.; Ferracuti, B.; Bovo, M.; Ligabue, V.; Vincenzi, Loris
abstract

La presente memoria descrive i danni ed i crolli osservati in edifici industriali prefabbricati dopo il terremoto dell’Emilia. Questo tipo di costruzioni, non progettato con criteri antisismici, si è rivelato particolarmente vulnerabile per diverse ragioni, come ad esempio l’assenza di sistemi di collegamento tra i vari elementi prefabbricati, l’inadeguatezza dei sistemi di collegamento tra pannelli prefabbricati esterni ed elementi portanti (pilastri e travi), l’interazione tra tamponamenti e pilastri ed, in alcuni casi, l’insufficienza delle fondazioni.

2012 - Vehicle-bridge interactive analyses on the Lagoscuro viaduct. [Relazione in Atti di Convegno]
Vincenzi, Loris; Savoia, M. Rossi F.
abstract

This paper presents the results of dynamic interaction analyses between vehicles and bridge, with reference to the case-study of the Pontelagoscuro viaduct. Different vehicle models with varying degrees of sophistication are presented to reproduce more accurately the effects of a train crossing a bridge. The results using the moving loads model and the vehicle-bridge interaction model are compared, and three-dimensional dynamic interaction analyses are performed to study also lateral and torsional vibrations of the Pontelagoscuro viaduct.

2011 - Structural monitoring of the Tower of the Faculty of Engineering in Bologna using MEMS-based sensing [Relazione in Atti di Convegno]
R., Guidorzi; R., Diversi; Vincenzi, Loris; C., Mazzotti; V., Simioli
abstract

Structural Health Monitoring (SHM) methodologies are taking advantage of the development of the new families ofMEMS sensors and of the progress in network technologies; future systems will rely on intelligent sensors performing locally datafiltering, elaboration and model identification, connected over suitable buses. This paper describes some families of multivariatemodels that can be used in SHM–oriented identification procedures and, in particular, the extension of AR models known asAR+noise. It describes also the implementation of a new advanced SHM system, the Teleco SHM602, in the tower of theEngineering School of Bologna University and the multivariate models identified from the data collected by this system.

2011 - The effect of local vibrations on fatigue in old steel riveted bridges. A case study: the Manhattan Bridge [Relazione in Atti di Convegno]
E., Pantoli; Vincenzi, Loris; M., Savoia; R., Testa
abstract

The present study is devoted to the effect on fatigue of vibrations induced by the train transit in an old railway steel bridge (the Manhattan Bridge in New York). It is shown how local vibrations can influence the crack growth and the remaining fatigue life of the bridge. A finite element model of the bridge is built and calibrated making use of available dynamic experimental data. Then, the actual fatigue loading spectrum is evaluated taking the actual traffic flows into account. Train transits on the bridge are simulated in order to find the structural elements where local vibrations can be significant. After having identified the members potentially subject to local vibrations, a substructure finite element model is studied for the detail. Starting from the stresses obtained in the detailed FE model, the crack growth is studied using Paris’s relationship.

2010 - Comportamento di nodi trave-colonna di strutture parzialmente prefabbricate [Relazione in Atti di Convegno]
C., Mazzotti; Vincenzi, Loris; M., Savoia; M., Ferrari
abstract

The results of an experimental program, devoted to the investigation of the structural behaviour of a precast RC beam-column node under cyclic loading, are described. The experimental activity is part of a research campaign developed to evaluate the seismic behaviour of a multi-story precast concrete system completed in situ. The experimental tests have been carried out by imposing cyclic quasi-static transverse displacements at the end sections of the beams. An axial load on the column is also applied, simulating the vertical load given by the permanent actions. The seismic performance of the node is experimentally studied. The hysteresis response and the strain profiles of the steel bars (longitudinal reinforcement and stirrups) within the node are recorded. The ductility of the connection and the cyclic strength degradation at prescribed displacement values are also evaluated.

2010 - Experimental Investigation on a Beam-Column Node of a Multi-Story Precast RC System [Relazione in Atti di Convegno]
C., Mazzotti; Vincenzi, Loris
abstract

The results of an experimental program, devoted to the investigation of the structural behaviour of a precast RC beam-column node under cyclic loading, are described. The experimental activity is part of a research campaign developed to evaluate the seismic behaviour of a multi-story precast concrete system completed in situ. The experimental tests have been carried out by imposing cyclic quasi-static transverse displacements at the two end sections of the beams. An axial load on the column is also applied, simulating the vertical load given by the permanent actions. The seismic performance of the node is experimentally studied. The hysteresis response and the strain profiles of the steel bars (longitudinal reinforcement and stirrups) within the node are recorded. The ductility of the connection and the cyclic strength degradation at prescribed displacement values are also evaluated.

2010 - Improving the speed performance of an Evolutionary Algorithm by a second-order cost function approximation [Relazione in Atti di Convegno]
Vincenzi, Loris; M., Savoia
abstract

In the present paper, dynamic identification problem of a FE structure with unknown parameters is solved by global search method. Response surface methodology is introduced in Differential Evolution algorithm to improve the performance of the algorithm. Differential evolution (DE) is an evolutionary algorithm where N different vectors collecting the parameters of the system are chosen randomly or by adding weighted differences between vectors obtained from two populations. In the modified algorithm, the new parameter vector is defined as the minimum of a second-order polynomial surface, approximating the cost function. Performance in term of speed rate is strongly improved by introducing the second-order approximation; nevertheless, robustness of DE algorithm for global minimum search of cost function is preserved, since multiple search points are used simultaneously. A numerical examples is presented, concerning identification of mechanical parameters of a steel truss girder bridge with unknown values of masses and stiffnesses of bracing and bearing.

2010 - Mems-based sensing for health monitoring of buildings [Relazione in Atti di Convegno]
R., Guidorzi; R., Diversi; Vincenzi, Loris; V., Simioli
abstract

Structural health monitoring is a field that relies on different technologies to realize systems that can characterize the dynamic properties of physical structures and identify possible deteriorations of their behavior. These systems include usually a data acquisition subsystem capable of recording the structural response to ambient or external loads and algorithms suitable for the analysis of the recorded response and for determining the dynamic properties of the monitored structures. This paper describes the results obtained in the preliminary analysis of the dynamic behavior of a structure constituted by a truncated middle-age tower presently included in an ancient palace of the XVI century located in the central part of Bologna.

2010 - Stabilità di tralicci PREM in prima fase [Relazione in Atti di Convegno]
Vincenzi, Loris; M., Savoia
abstract

The results of a numerical and analytical investigation on hybrid steel truss RC beams are described. Hybrid steel truss RC beams are beams where, during the construction phase and the concrete casting (Phase I), the steel truss system only carries the vertical loads. The steel truss of the beams may have different shapes, depending on the technology adopted, the span and the load. In this report, Steel trusses constituted by upper and diagonal bars and a steel plate at the bottom are considered. In construction phase, the verification against failure due to the safety against instability of the upper steel bars in compression or the diagonal elements is the most important design requirement. In the present study, four different beams are considered, with different steel trusses in Phase I condition. Finite Element modelizations of the beams are made and the failure loads are obtained, taking into account second-order effects due to large displacements. It is shown that the stability of the steel truss strongly depends on the lateral stiffness of the diagonal elements of the truss, as well as on the torsional rigidity of the lower steel plate. Starting from results of the numerical model, some design criteria are illustrated and discussed.

2010 - Utilizzo di MEMS per il monitoraggio strutturale [Relazione in Atti di Convegno]
Vincenzi, Loris; C., Mazzotti; R., Guidorzi
abstract

Structural Health Monitoring (SHM) is a filed that take advantage of the unprecedented development of sensor, microelectronics and microprocessor technologies. The new generation of SHM systems are based on MEMS (Micro Electro-Mechanical Systems) and relies on designs that integrate advanced sensor technologies with distributed computational power as well as efficient implementation of identification methodologies to realize “intelligent” sensors that elaborate local models and exchange data, information and models on a local network managed by a control/storage unit usually accessible also in a remote way. The purpose of this paper is to describe the results obtained from a MEMS-based sensing system starting from accelerations measured from a laboratory prototype and the preliminary analysis of the dynamic behavior of the tower of the Faculty of Engineering in Bologna. The results are shown comparing the MEMS based sensing system with a traditional system.

2009 - Comparison between coupled local minimizers method and differential evolution algorithm in dynamic damage detections [Relazione in Atti di Convegno]
Vincenzi, Loris; M., Savoia; G., De Roeck
abstract

In the present paper, performances of the Coupled Local Minimizers (CLM) method and the Differential Evolution (DE) algorithm for damage assessment of a cracked beam by FE model updating are compared. The presence of cracks in a structural member introduces local flexibilities modifying its dynamic behaviour. Changes in dynamic characteristics (frequencies and mode shapes) can be measured and subsequently used for damage detection. Comparison is performed by considering one crack first and two cracks in a second benchmark problem. The challenge is to find, by FE model updating, the crack location and the spring stiffness (related to the crack width). The effectiveness of two algorithms to find the set of optimization parameters has been compared by performing a statistical analysis of the optimization results.

2009 - Coupling of differential evolution algorithm and quadratic approximation for dynamic identification [Relazione in Atti di Convegno]
Vincenzi, Loris; M., Savoia
abstract

In the present paper, dynamic identification problem of a FE structure with unknown parameters is solved by global search method. Response surface methodology is introduced in Differential Evolution algorithm to improve the performance of the algorithm. Differential evolution (DE) is a evolutionary algorithm where N different vectors collecting the parameters of the system are chosen randomly or by adding weighted differences between vectors obtained from two populations. In the modified algorithm, the new parameter vector is defined as the minimum of a second-order polynomial surface, approximating the cost function. Performance in term of speed rate is strongly improved by introducing the second-order approximation; nevertheless, robustness of DE algorithm for global minimum search of cost function is preserved, since mul-tiple search points are used simultaneously. A numerical examples is presented, concerning identification of mechanical parameters of a steel-concrete bridge with unknown values of concrete elastic modulus, mass, and bearing stiffnesses.

2009 - Identificazione dinamica di una passerella pedonale strallata mediante algoritmi nel dominio delle frequenze [Relazione in Atti di Convegno]
Vincenzi, Loris; C., Mazzotti
abstract

Nella memoria sono presentati i risultati e l’interpretazione di prove dinamiche effettuate su una passerella ciclo-pedonale strallata sita nel comune di Imola. Le prove dinamiche sono state effettuate con eccitazione risultante da salti, corse e marce di pedoni oltre ad eccitazioni di tipo ambientale e misure di vibrazione in seguito a rilasci di una massa appesa alla struttura. Le caratteristiche modali della struttura sono state ottenute utilizzando due differenti tecniche nel dominio delle frequenze: la Enhanced Frequency Domain Decomposition (EFDD) e il MDOF Circle-fit method. Sono quindi stati posti a confronto i risultati ottenuti in termini di frequenze proprie, deformate modali e indici di smorzamento.

2009 - Inverse analysis for the calibration of FRP - Concrete interface law [Articolo su rivista]
Savoia, M.; Ferracuti, B.; Vincenzi, Loris
abstract

Inverse analysis technique is used to derive a non linear mode II interface law for Fiber Reinforced Polymer (FRP) – concrete bonding starting from experimental data. The proposed interface law is based on a fractional formula and includes non linear compliance contributions of adhesive and concrete cover at high shear stresses. It depends on three parameters (maximum shear stress, corresponding slip and an exponent), which are calibrated from experimental results on delamination tests. Values of maximum loads and strains profiles along FRP plates for different bonding lengths are used. Parameter identification is performed by inverse analysis using a Direct Search algorithm. Considerations on well-posedness of the inverse problem adopting different cost functions to minimize the error between experimental and numerical data are given. After parameter identification, numerical results obtained with the proposed interface law are found to be in very good agreement with experimental results.

2009 - Miglioramento sismico mediante sistemi dissipativi: il caso studio della scuola di Bisignano [Relazione in Atti di Convegno]
Vincenzi, Loris; M., Savoia
abstract

Nel presente studio, viene condotta l’analisi di vulnerabilità sismica di un fabbricato ad uso scolastico oggetto di monitoraggio da parte del Dipartimento della Protezione Civile. Il fabbricato presenta tamponature esterne e pareti divisorie interne con distribuzione simmetrica in pianta, ma significativamente diverse nelle due direzioni, ed in particolare con minor rigidezza nella direzione dei telai portanti in c.a. del fabbricato. È stato dapprima condotto un processo di identificazione delle proprietà di rigidezza dei tamponamenti a partire dai risultati di prove dinamiche. La struttura risulta particolarmente vulnerabile per livelli d’azione tali da indurre il danneggiamento dei tamponamenti, a causa di una ridotta capacità portante della struttura intelaiata alle azioni orizzontali Successivamente sono state condotte analisi numeriche dinamiche non lineari allo scopo di verificare l’efficacia dell’utilizzo di sistemi di dissipazione di energia (dampers o in alternativa controventi dissipativi) per l’adeguamento sismico della struttura.

2008 - Differential Evolution Algorithm for Dynamic Structural Identification [Articolo su rivista]
M., Savoia; Vincenzi, Loris
abstract

In the present paper, Differential Evolution algorithm is used to perform structural identification of mass and stiffness properties of civil structures from dynamic test results. Identification is performed initially starting from exact values of modal parameters (frequencies and mode shapes). Robustness of the algorithm is then tested by adopting pseudo-experimental input data, obtained by adding to exact data some statistic scattering, representing experimental measurement error. Different objective functions are adopted in identification procedure, and results are compared with those obtained adopting classical gradient method. The method is used to identify masses, elastic moduli and stiffnesses of external constraints of a RC frame structure and a steel – concrete bridge. Numerical results confirm that adopting both frequencies and mode shapes instead of frequencies only strongly increases sensitivity of objective function to identification parameters. Scattering of identified parameters is much smaller, with coefficient of variation of the same order of magnitude of that of pseudo-experimental data used as input values in dynamic identification procedure.

2008 - Il ruolo delle tamponature nel comportamento dinamico e sismico delle strutture intelaiate in c.a. [Relazione in Atti di Convegno]
Vincenzi, Loris; M., Savoia
abstract

Nel presente studio, viene condotta l’identificazione delle proprietà di rigidezza dei tamponamenti di un fabbricato ad uso scolastico oggetto di monitoraggio da parte del Dipartimento della Protezione Civile. Il fabbricato presenta tamponature esterne e pareti divisorie interne con distribuzione simmetrica in pianta, ma significativamente diverse nelle due direzioni, ed in particolare con minor rigidezza nella direzione dei telai portanti in c.a. del fabbricato. Nella procedura di identificazione, sono utilizzate le frequenze dei primi tre modi di vibrare, ed è impiegato il Modal Assurance Criterion (MAC) per associare correttamente le frequenze sperimentali e numeriche in funzione della correlazione tra i modi. È inoltre studiato il comportamento strutturale al variare del danneggiamento delle tamponature, modellato come una riduzione della rigidezza elastica delle bielle. È mostrato come, in una verifica agli stati limite di danno, i modi siano completamente differenti da quelli di una verifica agli stati limite ultimi, nella quale il contributo irrigidente delle tamponature viene tipicamente trascurato.

2008 - Stabilità in fase I del traliccio metallico delle travi reticolati miste [Relazione in Atti di Convegno]
Vincenzi, Loris; C., Mazzotti; M., Savoia
abstract

The results of a numerical and analytical in-vestigation on hybrid steel truss RC beams are described. Hybrid steel truss RC beams are beams where, during the construction phase and the concrete casting (Phase I), the steel truss sys-tem only carries the vertical loads. In this con-struction phase, the verification against failure due to the instability of the upper steel bars or diagonal elements is the most important design require-ment.In the present study, four different beams are considered, with different steel trusses in Phase I condition. Finite Element modelizations of the structure are made and failure loads are obtained, taking into account second-order effects due to large displacements. It is shown that the stability of the steel truss strongly depends on the lateral stiffness of the diagonal elements of the truss. Analytical models for the prediction of the fail-ure load are proposed, based on the instability of a beam on elastic foundation and the lateral buck-ling due to bending moment. Starting from the proposed analytical model, some design criteria are illustrated and discussed.

2007 - A second-order cost function approximation in differential evolution algorithm for structural identification [Relazione in Atti di Convegno]
Vincenzi, Loris; M., Savoia
abstract

In the present paper, dynamic identification problem of a FE structure with unknown parameters is solved by global search method. Response surface methodology is introduced in Differential Evolution algorithm to improve the performance of the algorithm. Differential evolution (DE) is a evolutionary algorithm where N different vectors collecting the parameters of the system are chosen randomly or by adding weighted differences between vectors obtained from two populations. In the modified algorithm, the new parameter vector is defined as the minimum of a second-order polynomial surface, approximating the cost function. Performance in term of speed rate is strongly improved by introducing the second-order approximation; nevertheless, robustness of DE algorithm for global minimum search of cost function is preserved, since multiple search points are used simultaneously. A numerical examples is presented, concerning identification of mechanical parameters of a steel-concrete bridge with unknown values of concrete elastic modulus, mass, and bearing stiffnesses.

2007 - Calibration of a mode II FRP-Concrete interface law by inverse analysis [Relazione in Atti di Convegno]
Savoia, M.; Ferracuti, B.; Vincenzi, Loris
abstract

Inverse analysis technique is used to derive a non linear mode II interface law for Fiber Reinforced Polymer (FRP) – concrete bonding starting from experimental data. The proposed interface law is based on a fractional formula and includes non linear compliance contributions of adhesive and concrete cover at high shear stresses. It depends on three parameters (maximum shear stress, corresponding slip and an exponent), which are calibrated from experimental results on delamination tests. Values of maximum loads for different bonding lengths and strains profiles along FRP plates are used. Parameter identification is performed by inverse analysis using a Direct Search technique. Considerations on well-posedness of inverse problem adopting different cost functions are given. After parameter identification, numerical results obtained with the proposed interface law are found to be in very good agreement with experimental results.

2007 - Identificazione dinamica di un viadotto della autostrada Salerno-Reggio Calabria mediante vibrazioni indotte dal traffico veicolare [Relazione in Atti di Convegno]
Vincenzi, Loris; C., Ceccoli; C., Mazzotti; M., Savoia
abstract

Nella presente nota si riportano i risultati di una prova dinamica effettuata su un ponte dell’autostrada Salerno-Reggio Calabria mediante vibrazioni indotte dal traffico veicolare. Frequenze proprie, deformate modali e smorzamenti sono stati ottenuti con un metodo a sottospazi che agisce nel dominio del tempo. Essi sono in grado di estrarre i parametri modali della struttura direttamente dai segnali ottenuti dalle registrazioni sperimentali provenienti da sensori posti sulla struttura (accelerometri nel caso in esame), senza dover misurare l’entità della forza eccitante. Successivamente si è confrontata la risposta con quella ottenuta con un modello agli elementi finiti allo scopo di verificare l’attendibilità dei risultati ottenuti.

2007 - Inverse analysis for calibration of FRP-Concrete interface law [Relazione in Atti di Convegno]
M., Savoia; B., Ferracuti; Vincenzi, Loris
abstract

Inverse analysis technique is used to derive a non linear mode II interface law for Fiber Reinforced Polymer (FRP) – concrete bonding starting from experimental data. The proposed interface law is based on a fractional formula and includes non linear compliance contributions of adhesive and concrete cover at high shear stresses. It depends on three parameters (maximum shear stress, corresponding slip and an exponent), which are calibrated from experimental results on delamination tests. Values of maximum loads for different bonding lengths and strains profiles along FRP plates are used. Parameter identification is performed by inverse analysis using a Direct Search technique. Considerations on well-posedness of inverse problem adopting different cost functions are given. After parameter identification, numerical results obtained with the proposed interface law are found to be in very good agreement with experimental results.

2007 - Investigation of ultimate capacity of beam-column joints of precast system [Capitolo/Saggio]
Vincenzi, Loris; C., Mazzotti; M., Savoia; C., Ceccoli; M., Ferrari
abstract

Results of an experimental campaign on precast reinforced concrete columns are described; multi-story columns are considered where, in the construction phase, vertical steel bars are designed to carry the full vertical load in beam-column joints. Under axial force and bending moment, failure of nodes is due to instability of steel bars. An analytical models for prediction of failure load is also proposed, where second-order effects and elasto-plastic behaviour of steel bars are taken into account. Axial force vs. horizontal displacement curves are provided, in good agreement with experimental findings. Experimental results are also compared with numerical results obtained from a non-linear FE model. Starting from the proposed analytical model, some design criteria are illustrated and discussed.

2006 - Identificazione dinamica attraverso algoritmi di ottimizzazione evolutiva [Relazione in Atti di Convegno]
Vincenzi, Loris; M., Savoia
abstract

In questa memoria sono presentati i risultati ottenuti dall’identificazione dinamica di un modello agli Elementi Finiti di un ponte in struttura mista acciaio-calcestruzzo. I valori ottimi di massa e rigidezze sono stati ottenuti mediante un algoritmo evolutivo, il Differential Evolution Algorithm.

2006 - Modal identification of a TAV viaduct using subspace models [Relazione in Atti di Convegno]
Vincenzi, Loris; C., Mazzotti; M., Savoia
abstract

In the present paper, the dynamic behaviour of a TAV viaduct of Italian high-speed railway close to Modena (IT) is investigated. The viaduct consists of precast single C concrete beams with span 31.50 meters long and 9.00 meters wide (Fig. 1A). Clean span is 29.00 meters long. Beams are simply-supported to cantilever circular piers with 3.50 meters diameter. Beam cross section consists of a concrete deck 0.60 meters thick and lateral wings 0.7 to 0.8 meters thick. The main purpose of this study is the characterization of dynamic behaviour of the viaduct using both time domain and frequency domain methods. Identified parameters are modal frequencies, mode shapes and damping ratios. Results obtained adopting different time and frequency domain methods are compared.Experimental natural frequencies, modes and damping ratios have been evaluated starting from Frequency Response Function (FRF) by using the MDOF Circle Fit Method and Auto-Regressive Moving Average Vector (ARMAV) models.

2005 - Differential evolution algorithm in dynamic structural identification [Relazione in Atti di Convegno]
M., Savoia; Vincenzi, Loris
abstract

In the present paper, a Differential Evolution algorithm is used to perform a structural identification of mass and stiffness properties of a frame structure. Identification is performed starting from exact data and, alternatively, from pseudo-experimental data, obtained by adding some statistic scattering to exact data. Different object functions are adopted and results are compared with those obtained adopting classical gradient method. Numerical results confirm that adopting both frequencies and modal shapes instead of fre-quencies only strongly increases the sensitivity of object function to identification parameters. Results ob-tained are then much less scattered, with coefficient of variation of the same order of magnitude of that of pseudo-experimental data.

2005 - Identificazione dei parametri modali autoregressivi di un modello ARMA Vettoriale attraverso algoritmi evolutivi [Relazione in Atti di Convegno]
Vincenzi, Loris; M., Savoia
abstract

In questa memoria viene presentato l’utilizzo di un algoritmo evolutivo per l’identificazione dei parametri autoregressivi di modelli ARMA vettoriali per la caratterizzazione dinamica di strutture sottoposte a eccitazione ambientale. Per valutare le proprietà modali della struttura occorre risolvere il modello ARMA ricercando i coefficienti autoregressivi propri del modello. Il metodo di identificazione parametrica conosciuto come Prediction Error Method (PEM) consente di stimare tali parametri, attraverso la minimizzazione della funzione errore di predizione. A causa della non linearità del problema di minimizzazione, soprattutto quando il numero di segnali in uscita è elevato, i metodi di identificazione che si basano sul gradiente risultano inaccurati in quanto presentano problemi di convergenza nei casi di bassa sensitività della funzione errore nei riguardi dei parametri da identificare. Nel presente studio è stato adottato, per l’identificazione dei parametri autoregressivi di un modello ARMA Vettoriale, un algoritmo evolutivo, il Differential Evolution Method, indicato per la ricerca di minimi anche quando la funzione costo è definita implicitamente.

2005 - Identificazione dinamica di una struttura di acciaio mediante vibrodina [Relazione in Atti di Convegno]
C., Mazzotti; Vincenzi, Loris
abstract

Nella presente nota si riporta un esempio applicativo di una metodologia di identificazione basata su prove vi vibrazione forzata. Vengono descritti i risultati di una prova dinamica con vibrodina effetuata su una porzione dell’ampliamento del Politecnico di Torino a struttura metallica: dai dati sperimentali si sono calcolate le funzioni di risposta in frequenza che hanno fornito frequenze proprie e deformate modali. Successivamente si è confrontata la risposta con un modello agli elementi finiti correlando modi propri e frequenze.

2005 - Structural identification of a steel structure by forced vibrations [Relazione in Atti di Convegno]
C., Mazzotti; Vincenzi, Loris
abstract

In the present paper, an application of a dynamic identification process in the frequencies domain, is presented. A steel structure 90 meters long, 22 meters high and simply supported by four pair of concrete piles is considered. The structure has been dynamically loaded by using a mechanical shaker, giving si-nusoidal excitation at prescribed frequency values. Experimental modal frequencies, deformations and damping ratios are evaluated starting from inertance function by using the MDOF Circle Fit Method. A finite element model of the structure has been developed and Modal Assurance Criterion (MAC) is, then, used to compare experimental and numerical vibration modes; good correlation is obtained both for global flexural modes, global torsional modes and longitudinal modes.

2004 - Identificazione di una struttura da ponte acciaio-calcestruzzo mediante prove di vibrazione forzata [Relazione in Atti di Convegno]
C., Mazzotti; Vincenzi, Loris; M., Savoia; R., Poluzzi
abstract

Nella presente nota si riportano i risultati di una prova dinamica effettuata mediante vibrodina su un ponte in struttura mista acciaio-calcestruzzo: dai risultati sperimentali si sono calcolate le funzioni di risposta in frequenza poi interpolate per ricavarne frequenze e deformate modali. Successivamente si è confrontata la risposta con un modello agli elementi finiti e sono stati ottenuti i valori ottimi di parametri meccanici (modulo elastico del calcestruzzo e rigidezza dei vincoli) correlando modi propri e frequenze.