Contribution of anthropogenic consolidation processes to subsidence phenomena from multi-temporal DInSAR: a GIS-based approach

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

Dynamic Assessment of Masonry Towers Based on Terrestrial Radar Interferometer and Accelerometers

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

Human-structure interaction effects on the maximum dynamic response based on an equivalent spectral model for pedestrian-induced loading

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

Mitigation of model error effects in neural network-based structural damage detection

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

Ottimizzazione multi-obiettivo di modelli a elementi finiti: criteri per la scelta della soluzione ottimale

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

Dynamic behaviour of the San Felice sul Panaro Fortress: Experimental tests and model updating

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

Bayesian Model Updating and Parameter Uncertainty Analysis of a Damaged Fortress Through Dynamic Experimental Data

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

Dynamic Identification and Model Updating of a Masonry Chimney

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

Human-induced vibrations of a curved cable-stayed footbridge

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

Dynamic identification of an ancient masonry bell tower using a MEMS-based acquisition system

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