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The paper delivers a short report about the modal identification carried out on a historical masonry palace in the city centre of L’Aquila, Palazzo Pica Alfieri, retrofitted after the 2009 earthqua...

Purpose Using the da Vinci Research Kit (dVRK), we propose and experimentally demonstrate transfer learning (Xfer) of dynamics between different configurations and robots distributed around the world. This can extend recent research using neural networks to estimate the dynamics of the patient side manipulator (PSM) to provide accurate external end-effector force estimation, by adapting it to different robots and instruments, and in different configurations, with additional forces applied on the instruments as they pass through the trocar. Methods The goal of the learned models is to predict internal joint torques during robot motion. First, exhaustive training is performed during free-space (FS) motion, using several configurations to include gravity effects. Second, to adapt to different setups, a limited amount of training data is collected and then the neural network is updated through Xfer. Results Xfer can adapt a FS network trained on one robot, in one configuration, with a particular instrument, to provide comparable joint torque estimation for a different robot, in a different configuration, using a different instrument, and inserted through a trocar. The robustness of this approach is demonstrated with multiple PSMs (sampled from the dVRK community), instruments, configurations and trocar ports. Conclusion Xfer provides significant improvements in prediction errors without the need for complete training from scratch and is robust over a wide range of robots, kinematic configurations, surgical instruments, and patient-specific setups.

The development of realistic numerical models able to replicate as closely as possible the actual structural behaviour of heritage buildings is crucial for a thorough assessment of their structur-al performance against exceptional scenarios. In this regard, higher accuracy can be achieved by leveraging a multidisciplinary approach that integrates multiple contributions from different fields, such as geomatics, dynamics and computational modelling. In the present paper, this strategy is applied to the tower keep of the Guimarães castle, in Por-tugal, a masonry fortified structure dating back to the X century. Starting from an accurate la-ser scanner survey, a detailed numerical model has been created resorting to efficient algo-rithms able to represent complex situations. Furthermore, by exploiting the dynamic properties extracted from the processing of vibration data collected during field dynamic testing, the me-chanical characteristics of the constituent materials of the tower have been estimated by means of a model updating technique embedded in a trust-region scheme implemented in the NOSA-ITACA code. The results obtained so far allowed to establish valuable baseline information that will be of pivotal importance to catch possible changes in the tower's response and to perform more in-depth structural analyses.

Despite the use of rammed earth became marginal in the second half of the past century, Portugal still holds an important built heritage. Recently, a growing use of rammed earth has been observed in modern constructions, but it is putting aside the roots of traditional rammed earth construction. The seismic behaviour of rammed earth buildings is still insufficiently comprehended, constituting a matter of great concern, since most of the traditional dwellings are built on regions with important seismic hazard. Moreover, the complex architecture of modern rammed earth buildings is expected to make their seismic behaviour even more fragile. This paper intends to provide a better comprehension on the seismic behaviour of rammed earth constructions from Portugal. For this purpose, twenty traditional dwellings were evaluated on the basis of a simplified approach, while a modern construction was investigated by means of destructive and non-destructive testing approaches. The main findings of these approaches are discussed in detail, but it can be highlighted that the architectural features of traditional rammed earth buildings benefit their seismic behaviour, while the complex architecture of modern rammed earth buildings demands using advanced engineering tools for their seismic assessment., This work was partly financed by FEDER funds through the Competitivity Factors Operational Programme - COMPETE and by national funds through FCT Foundation for Science and Technology within the scope of projects POCI-01-0145-FEDER-007633 and POCI-01-0145-FEDER-016737 (PTDC/ECM-EST/2777/2014). The support from grant SFRH/BPD/97082/2013 is also acknowledged. The authors wish also to express gratitude to Eng. Sergio Morgado and Mr. Francisco Seixas for providing access to the house of Forjales and conditions to perform the destructive and non-destructive tests., info:eu-repo/semantics/publishedVersion

The dynamic monitoring of multi-leaf masonry wall is here proposed. The results of nondestructive tests carried out in this work are a first part of a wider testing campaign aimed at verifying the structural performance of masonry walls. Multi-leaf masonry walls constitute the composite construction typology most widely adopted in historic buildings. This aspect, together with the intrinsic structural complexity, heterogeneity and irregularity, directs the present research towards a topic not yet sufficiently investigated by the scientific community. In this paper, the case of multi-leaf masonry wall has been investigated, and with the aim of reproducing historical buildings structural elements, three different typologies of multi-leaf masonry walls have been considered: (i) full infill, (ii) damaged infill, (iii) consolidated infill. Several masonry specimens of the above-described typologies have been built and tested in lab. The dynamic parameters, such as frequencies, modal shapes and damping ratios have been identified through the output-only procedure and the data were processed through the Least Square Complex Frequency (LSFC) estimator; the analysis of results allowed to evaluate the structural integrity, the efficacious of consolidating intervention and the potential performance mechanisms of different complex multi-leaf masonry walls. Experimental results are compared with numerical Finite Elements models. Composite multi-leaf masonry is modelled as an equivalent continuum obtained through a full 3D homogenization procedure. The mechanical properties of component materials have been obtained in lab by tests and then used to model the masonry at the micro-scale in order to derive the mechanical properties to be adopted at macro-scale. A parametric natural frequencies analysis is performed in order to calibrate the model by the comparison whit the experimental measures.

The perceptible vibration of concrete box girders under traffic loads is an important topic in existing bridges, on which vehicle movement often cause vibrations too strong from the viewpoints of travelers. In this paper, the results of an extensive program of full-scale ambient vibration tests involving a 380 m concrete box girder bridge, the Cannavino bridge in Italy, are presented. The human safety assessment procedure of the bridge includes ambient vibration testing, identification of modal parameters from ambient vibration data, comparison with a detailed finite element modeling as validation of experimental measurements, comparison of peak accelerations to reference values from technical standards/literature in order to estimate the vibration level, and evaluation of safety by the use of histograms. A total of nine modal frequencies are identified for the deck structure within the frequency range of 0–10 Hz. The results of the ambient vibration survey are compared to the modal frequencies computed by a detailed three-dimensional finite element model of the bridge, obtaining a very good agreement. It emerges that a linear finite element model appears to be capable of capturing the dynamic behavior of concrete box girder bridges with very good accuracy. For each direction, experimental peak accelerations are compared to acceptable human levels available in technical standards/literature, showing that traffic loads mainly induce a vertical component of vibration on the bridge deck. Finally, the elaboration of histograms allows to assess that the bridge is exposed to clearly perceptible vertical vibrations, requiring the adoption of suitable vibration reduction devices.

The papers focusing on dynamic identification of structural damages usually rely on the comparison of two or more responses of the structure; the measure of damage is related to the differences of the vibration signals. Almost all literature methods assume damping proportionality to mass and stiffness; however, this is acceptable for new, undamaged structures, but not for existing, potentially damaged structures, especially when localised damages occur. It is well-known that in non-proportionally damped systems the modes are no longer the same of the undamped system: thus, some authors proposed to use modal complexity as a damage indicator. This contribution presents a perturbation approach that can easily reveal such a modal complexity.

Compared with other diagnostic techniques, which are limited to the local investigation, the structural dynamic monitoring allows to obtain information about seismic response and vulnerability of structures, in their whole. The experimental modal analysis evaluates the dynamic parameters such as frequencies, vibration modes and damping coefficients. For historic buildings, due to their heterogeneity and complexity, these data are not yet readily available. The possibility of applying the simplified procedures for the dynamic identification of the different historic structural typologies is, therefore, strategic to obtain useful information to apply the design criteria and the structural verifications in the seismic field. Besides the simplified procedures allow an optimization both on the execution time and on the costs. The paper provides some hypothesis of simplified dynamic monitoring procedures through the reduction/optimization of the accelerometric sensors used for three case studies, which differ in structural typology such as Churches, Towers and Palaces.

This paper presents the analysis of the dynamic performances of a simple model related to a squat masonry tower situated in the Swabian Castle of Trani (Italy). The main objective of this paper is to introduce a novel strategy based on a simple model validated by experimental data for defining the influence of the excitation frequency on the structural damping dynamic transmission. To this aim, first, the accelerations have been acquired simultaneously in 23 points of the tower at different levels, both due to environmental vibrations and due to a series of sinusoidal forced vibrations applied at the base by using an electro‐hydraulic shaker device specifically designed for the tests. Four different excitation frequencies have been then selected for exciting the structure. An operational modal analysis has been carried out by the environmental recordings and with the different forcing loads obtaining a very good correlation of the identified frequencies in all the cases. Then a digital filtering process has been applied over all the recorded signals to evaluate the specific contribution for each frequency generated by the shaking device at each level of the tower. Increments of damping ratio have been detected with these forced vibrations at the base. Finally, a simple frame numerical model has been developed to reproduce the dynamic amplification at the most significant locations of the tower. It has been updated not only to have the same main frequencies and modal shapes but also to get a similar response under forced vibrations at the base. A good correlation has been obtained between the model and the real structure for the base forced vibrations at different excitation frequencies in order to correctly predict the dynamic behaviour of the structure. Authors acknowledge the Italian project PRIN 2015: “Mitigating the impacts of natural hazards on cultural heritage sites, structures and artefacts” and the Spanish project BIA2015‐69952‐R.

The study of the structural behaviour of damaged RC buildings during ground motion is a fundamental topic in the modern earthquake engineering. Many studies have been carried out in order to better understand the real evolution of the damage in RC buildings during a seismic event. In this work, a damaged RC building has been intensively investigated in terms of materials property and stiffness evolution in order to interpreting the structural and nonstructural surveyed damage. The peculiarity of this building is its damage sequence during the 2002 Molise earthquake. In fact, the town of Bonefro suffered moderate damage (MCS intensity VII), with the exception of the investigated reinforced concrete building. The October 31, 2002 event (M=5.4) caused some structural damage to this building. The second event (M=5.3), on November 1, 2002, increased substantially the damage level (grade 4 according to the 1998 European Macroseismic Scale). It occurred just while, due to fortuitous circumstances, a 5. min. seismic velocimetric recording was being taken. The working group has performed some frequency analyses based on the recording. Several non linear models have been defined to understand the damage evolution of the building and the local and global damage patterns through for static analyses. Finally, linear and non linear models have been developed with the main goal of identifying the characteristics of a reliable undamaged structural model. © 2014 Elsevier Ltd.

Historical towers, in particular medieval towers, are an important part of cultural heritage, and their preservation mandates monitoring and detailed analyses of vulnerability under seismic actions as well as of their long-term performance. Certain aspects of structural nature are linked to the masonry behavior as a unilateral material, and other are aspects related to the interaction with soft soil conditions. This study aims to contribute to the aspects of preservation by exploring the role of the soil-structure interaction in predicting the behavior of the structures, with specific reference to the well-documented case history of the medieval Ghirlandina Tower (Modena, Italy). A significant contribution comes from an experimental identification analysis, performed in the presence of ambient vibration. A novel finding is that the soil structure interaction cannot be neglected, in contrast to most published identification analyses that usually assume the structure to have rigid constraint at base.

The present paper focuses on the use of a 3D motion capture system for the dynamic identification and the damage monitoring of a 1:10 scaled mock-up (representing the large historic masonry structure of Hagia Irene, Istanbul) tested on shaking table at the ENEA Casaccia Research Center located near Rome, Italy. The dynamic identification of the structure during the shaking table tests was obtained by several techniques of Experimental Modal Analysis (EMA), such as FRF, FDD and EFDD. To such purpose Displacement Data Processing (DDP) of a large number of markers of the 3DVision (the passive 3D motion capture system installed at the ENEA laboratory) was performed. Markers were located on the tested mock-up accordingly to the indications of preliminary FEM analysis and modal shapes. Also conventional accelerometers were placed on the physical model and used as reference for the analysis of 3DVision data. In addition, the analysis of Markers Relative Displacements (MRDs) was useful to detect the occurrence and development of fractures during the tests, contributing to assessing the actual progress of the structural damage. The results from EMA techniques and MRDs analysis of 3DVision data are illustrated, showing the potentialities of this monitoring system in integrating the two complementary approaches.

The paper shows the results of monitoring activities to check the structural response and the level of damage of two historic monument of LAquila: San Pietro di Coppito and Santa Maria Paganica, that were damaged by the main earthquake of April 2009. The diagnostics operation was planned and carried out in situ and in laboratory to verify the integrity of the residual stiffness of the structures and to define the mechanical parameters of the material. The mechanical characterization of materials was carried out through destructive tests on samples, taken directly on site, and micro-destructive tests through single and double flat jacks. To give a first qualitative assessment of overall was used sonic test (non-destructive test) on the main macro-structure. The global structural health monitoring (SHM) was carried out through ambient vibrations to define the real dynamic behavior in serviceability state and to calculate - via a modal identification of output-only systems-the dynamic parameters (mode of vibration, frequencies, displacements and damping ratios). The aim of this research is to prove the reliability of different diagnostic methodologies, the real extent of global and local damage and the extent of the residual stiffness of the macro elements of the structures (façade, tower, walls of nave, transept) that are subjected to different mechanism of failure.

The functionality maintenance of European infrastructures like bridges is acquiring more and more importance due to the huge economic losses related to the interruption of their regular service. In particular, fatigue represents one of the most common failure modes occurring in steel and steel–concrete composite bridges: most failures in steel structures are related to fracture and fatigue. Railway bridges endure millions of stress cycles during their life and they are expected to be highly vulnerable to such phenomena. Phenomena like ‘vibration induced’ and ‘distortion induced’ fatigue are still partially uncovered by actual design codes and they represent critical aspects for the assessment of existing bridge remaining life and for the design of new bridges. The European research project FADLESS ‘Fatigue damage control and assessment for railways bridges’, funded by the Research Fund for Coal and Steel, aims at defining innovative technical guidelines for the assessment and control of existing and new b...

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

Revista ciêntífica: Procedia Engineering, Volume 199, 2017, Pages 2178-2183, These last decades have seen an exponential increase in the amount of research related to structural health monitoring (SHM) due to its potential for significant life-safety and economic benefits. However, the success of this powerful tool strongly depends on the implemented damage identification strategy. Reliable and efficient damage identification algorithms enable to detect faults that lie beneath the surface of the structure and to spot system’s vulnerabilities at a very early-stage. This allows to adopt appropriate remedial measures in a timely fashion thereby minimizing the risk of unexpected collapses. The present paper describes a spectrum-driven damage identification method that investigates three levels of damage, i.e. detection, localisation and assessment. Peculiarity of the method is the use of spectral frequency-dependent Eigen-parameters estimated from the response Power Spectral Density (PSD) matrix, which is demonstrated to be very sensitive to damage-induced changes. The approach is detailed, including initial assumptions, scientific formulation of the problem and derivation of the algorithm. Finally, the effectiveness of the method is validated through a numerical simulation and verified on a case-study structure., FEDER funds through the Competitiveness Factors Operational Programme - COMPETE a n d by national funds through FCT – Foundation for Science and Technology within the scope of the project POCI-01 -0145-FEDER-007633., info:eu-repo/semantics/publishedVersion

The structural characterization of tie-rods is crucial for the safety assessments of historical buildings. The main parameters that characterize the behavior of tie-rods are the tensile force, the modulus of elasticity of the material and the rotational stiffness at both restraints. Several static, static–dynamic and pure dynamic nondestructive methods have been proposed in the last decades to identify such parameters. However, none of them is able to characterize all the four mentioned parameters. To fill this gap, in this work a procedure based on dynamic testing, added masses and genetic algorithms (GA) is proposed. The identification is driven by GA where the objective function is a metric of the discrepancy between the experimentally determined (by dynamic impact testing) and the numerically computed (by a fast and reliable finite element formulation) frequencies of vibration of some modified systems obtained from the tie-rod by adding a concentrated mass in specific positions. It is shown by a comprehensive numerical testing campaign in which several cases spanning from short, low-stressed, and almost hinged tie-rods to long, high-tensioned, and nearly clamped tie-rods, that the proposed strategy is reliable in the identification of the four unknowns. Finally, the procedure has been applied to characterize a metallic tie-rod located in Palazzo Paleotti, Bologna (Italy).

This work addresses the seismic safety of the remainings of one church in Famagusta (Cyprus), including also a historical survey, inspection and diagnosis. The seismic safety is studied in detail, using limit analysis of collapse mechanisms as preliminary safety assessment. Then, a finite element model was prepared and updated using dynamic identification results. The updated model was subjected to non-linear static (pushover) analysis in different directions (global and principal) using two lateral load patterns: proportional to the mass and proportional to the modal shapes of the structure. Finally, a time history analysis is also performed. The results allow to conclude that: (a) limit analysis of collapse mechanism can be adequately employed for the seismic assessment of masonry ruins, as they provide comparable results to more sophisticated analysis; (b) load patterns proportional to the mode shapes in pushover analysis of complex masonry structures should be carefully considered, as they can provide too conservative results; (c) the ruins of the church exhibit a low seismic safety., This work was partly funded by project FP7-ENV-2009-1-244123-NIKER of the 7th Framework Programme of the European Commission Project.

This work shows the results of monitoring of Santa Maria del Suffragio (Anime Sante) church, L’Aquila, Italy. The historical building was stricken and damaged by mainshock of April 6, 2009; the dome is the structural element that has been seriously hit by seismic event. The ambient response analysis of global structure and dome element enable to improve the FE model by model updating methodology using modal data. The identification techniques furnish useful information concerning the structural and mechanical properties of dome’s structure, these parameters are needed to evaluate the appropriate design of rebuilding and structural rehabilitation of dome. The geometric configuration and the self-weight of lantern induce to an independent dynamic response of macro-element against the behaviour of dome generating the first mechanism of collapse and the failure of dome shape. Different retrofitting configurations for the dome have been proposed in this paper.

The paper is related to the San Torcato Church, in Guimarães, Portugal. At the moment, the church has significant structural problems due to soil settlements. Cracks can be observed on the main and the lateral façades, the bell-towers are leaning, and the arches in the nave exhibit a failure mechanism with cracks and vertical deformations. Non-stabilized phenomena are present in the structure. To stabilize the damage, a structural intervention is planned to occur soon and the church is already monitored to follow the intervention. The paper clearly presents the problem with emphasis to the dynamic analysis carried out before the structural strengthening, namely: the experimental tests with output-only techniques for frequencies, damping and mode shapes estimation, FE model updating analysis and dynamic monitoring

The Tanaro Bridge, an 18 span masonry bridge built in 1866, has been investigated both in service conditions and at different stages of its demolition. A comparative characterization of the brickwork was performed by means of compressive tests on cylinders, flat jacks, sonic and sclerometer tests, while the natural frequencies and mode shapes of the bridge and the brickwork damping have been identified by dynamic tests on the bridge. Data from material testing were used to set up FEM models, so that the reliability of the material characterization procedures is demonstrated by comparison between the dynamic tests and FEM results. A rational comparative analysis of the results showed that: (i) a large part of the bridge needs to be monitored if the mode shapes are to be identified through dynamic tests; (ii) elastic FEM models can provide some information on the bridge response under service loads provided the mechanical parameters are adequately identified. Besides, some information has been deduced on the effectiveness, in service conditions, of some retrofitting technique: (i) transversal tie bars through the arch thickness have been proved almost ineffective; (ii) internal spandrels were found to be quite efficient in connecting adjacent spans.

The present study deals with dynamic identification and model updating of the Howa brick chimney to preserve brick chimneys. From the results of dynamic tests, the fundamental frequencies of the Howa brick chimney are estimated to be about 3.06Hz and 2.69Hz in north-south and east-west directions, respectively. The natural modes and damping factors are identified by ARMAV (auto-regressive moving average vectors) model. The numerical model updating based on IEM (inverse eigensensitivity method) is applied to two models with two updating procedures; using only frequencies and both frequencies and mode shapes. The updating results show the mode shapes are very important to obtain the good results for the numerical model updating. From the results of the numerical model updating, the damaged areas are identified; these are found to correspond well to the position of the cracks of the static collapse test.

The recent earthquakes in Italy demonstrated the extreme vulnerability of historical and cultural structures. Masonry vaults, which represent artistically valuable elements of these constructions, have been recognised among the most vulnerable elements. Traditional vault retrofit methods, such as buttresses or ties, are still widely adopted. These retrofit methods prevent differential displacements between vault supports (e.g., abutments, masonry piers and loadbearing walls). However, the pier differential displacement is not the only vulnerability source for vaults, and in many cases, further retrofit interventions are needed. Innovative retrofit methods based on inorganic matrixes, such as IMG, are aimed to prevent hinge mechanism failures. Such methods are suitable to be applied on vaults already retrofitted using traditional methods. The knowledge of the seismic behaviour of a vault, once the differential displacement between the supports is prevented, can be crucial to the assessment of potential further vulnerabilities of vaults already retrofitted with traditional methods. However, a deep knowledge of vault seismic behaviour is still lacking from an experimental point of view. Indeed, to date, few dynamic experimental studies have been conducted. Therefore, to investigate the seismic behaviour of masonry barrel vaults, several shaking table tests were performed on a full-scale specimen before and after the retrofit interventions. The tests investigated the main seismic properties of the tested structure and clarified the cracking mechanisms and capacity improvement due to the retrofit interventions. A comprehensive overview of the main results of the experimental tests has been presented.

This research demonstrates an integrated non-invasive assessment method of monumental structures based on dynamic monitoring through ambient vibrations as well as non destructive and microdestructive testing. The investigation involves the analysis of a very complex and extraordinary case study, i.e., the Rialto Bridge in Venice. Dynamic monitoring based on natural vibration sources as inputs from pedestrian traffic, wind and the waves of the Canal Grande – was exploited by dynamic identification process to determine damping coefficient, frequency and modal shapes. The non-destructive and microdestructive tests included sonic and georadar methods and the extraction of very small samples of masonry for destructive tests in laboratory. The experimental investigation on the whole was conceived to avoid any type of invasive action on the prestigious monument. The aim of this research is to propose a new integrated protocol potentially suitable and generalizable for the assessment of monumental structures. The new features in the combined method include two types of results – qualitative and quantitative types – through a flow chart to explain the methodology and generalize the different phases of the approach for historical constructions.

Soil–structure interaction quite often plays a major role in the seismic response of masonry towers and this paper presents a simple but consistent framework for this kind of analysis. Using experimental data from a monitoring system installed on the Ghirlandina tower, it is shown that simple models can provide reliable estimates of the input motion and of the dynamic stiffness of the soil–foundation system. In this specific case, it is proved that the foundation input motion can be evaluated by neglecting the kinematic interaction between the foundation and the surrounding soil. Moreover, the classical computation approaches of the foundation dynamic stiffness lead to results in agreement with the response of the tower, if the effects of soil non-linearity are accounted for. The validation is provided considering three seismic events, which have been recorded by the monitoring system and by a free-field accelerometric station in the vicinity of the tower.

The purpose of this paper is to study the dynamic behavior of a pedestrian bridge in Alicante, Spain, which showed vertical and horizontal vibration problems. Moreover, the deck’s structural steel showed severe corrosion damage. Hence, two cases were analyzed: before retrofitting the structure using glass fiber-reinforced polymers (GFRPs) and after. While the GFRP was designed for aesthetic and durability purposes only—and not for structural retrofitting—it changed the mass and stiffness of the footbridge, affecting its dynamic characteristics. The natural frequencies, mode shapes, and modal damping factors of the bridge were calculated based on accelerations recorded at 11 points on the bridge under different conditions—i.e., ambient vibration and forced vibration produced by a fixed number of pedestrians walking on the bridge at a certain speed and frequency. A numerical model was also designed in order to compare the experimental and numerical results.

The seismic events in the last decades evidenced the vulnerability of the architectural heritage with respect to these phenomena. Therefore, timely provisional and permanent interventions are often required in post-seismic scenarios.In response to the call for more efficacious solutions, a great deal of interest has been given to glass fiber-reinforced polymers (GFRPs) composite. GFRP composites offer the advantage of high strength, low self-weight and durability.This research proposes some first evaluations on the dynamic behaviour of pultruded FRPs (Fiber Reinforced Polymers) strut and tie spatial structure for seismic protection of historical building heritage. The dynamic identification has been carried out using the ambient vibrations test to measure the mode of vibration, frequencies, displacements and damping ratios of the structures. The Operational Modal Analysis (OMA) has been carried out to identify the modal characteristics through poly-reference Least Square Complex Frequency-domain (pLSFC) estimator.Basing on the experimental results the dissipative capacity has been evaluated through the calculation of the behaviour factorq.The experimental dynamic parameters were used to calibrate a numerical finite element model employed under the hypothesis of kinematic equivalence to evaluate theqfactor considering the elastic-brittle behaviour of FRP material. The dissipative capacity of structure was assigned to the global geometric configuration - frame with concentric diagonal bracings - through the strength hierarchy criteria locating the dissipative zones in the tensile diagonals. The analysis was carried out considering some typological variations to investigate the variability of the behaviour factorq.

The dissipation capacity of a generic structure depends on its many characteristics – like material, shape of the cross-sections, structural scheme, regularity and typology of structures – and it is accomplished by means of the behavior factor q through a very strategic reduction of seismic action. This is the reason why this research shows an overview on the evaluation of the q factor, preparatory to an analysis related to a spatial frame structure of built-up members made of FRPs (Fiber Reinforced Polymers) pultruded profiles, FRP gusset plates and steel bolts. The factor q proposed starts directly from experimental data, in detail the outcomes due to the dynamic identification on site carried out. Subsequently, a finite element model under the hypothesis of kinematic equivalence for the measurement of q was calibrated. The adopted structure investigated is a spatial frame with concentric diagonal bracings for which its dissipation capacity by means of the strength hierarchy criteria was assigned. To exalt the overall behavior of the all-GFRP structure a case of rigid connection is assumed with a comparison with semi-rigid conditions. The analysis was carried out also on the variability of the q factor, considering some typological variants of the basic structure.

Damage detection in civil engineering structures using changes in measured modal parameters is an area of research that has received notable attention in literature in recent years. In this paper two different experimental techniques for predicting damage location and severity have been considered: the Change in Mode Shapes Method and the Mode Shapes Curvature Method. The techniques have been applied to a simply supported finite element bridge model in which damage is simulated by reducing opportunely the flexural stiffness EI. The results show that a change in modal curvature is a significant damage indicator, while indexes like MAC and COMAC – extensively and correctly used for finite element model updating - lose their usefulness in order to damage detection.

of the motor is provided by applying Operational Modal Analysis (OMA) methodologies able to estimate the modal parameters of the structure undergoing its operative conditions. The sensitivity of the OMA approaches to deal with structures characterized by time-dependent parameters is evaluated through a numerical simulation. Moreover, a comparison between the estimates from dierent state-of-the-art approaches in OMA (operating in both time and frequency domain) are provided. The capabilities of the OMA methods to track the changes in the natural frequencies, damping ratios and mode shapes of the rst stage of the Vega lunch vehicle will be investigated in order to asses the overall eciency of such approaches.

The FADLESS research project aims to define innovative technical guidelines for the assessment and control of existing and new bridges with regard to fatigue phenomena induced by vibrations and distortions produced by the passage of trains. The project will employ the most recent experimental and numerical techniques in order to identify the most typical details frequently subjected to high fatigue effects and to draft technical guidelines suitable of controlling such effects during bridge design or assessment. As part of the research project, this paper describes some results concerning the fatigue assessment of the Lagoscuro railway viaduct. The Lagoscuro viaduct is composed of two parallel steel railway viaducts crossing the Po river. The first viaduct was built in 1948 and is composed of nine single span truss-girder bridges; the upper and the lower chord, diagonals and struts of the main truss girders are composed of four L-shaped steel elements, riveted together by means of plates; stringers and additional elements supporting the railway lines are also riveted. The new Lagoscuro viaduct was recently built in order to improve the railway line; the same geometry has been adopted but, different to the old viaduct, the truss girders are composed of H-shaped elements welded or bolted together in the joints. First, the results of the experimental dynamic tests [1] are performed in order to identify the modal properties of both viaducts. Then, global finite element models are corrected according to the model updating procedures, where the uncertain model properties are adjusted in order to obtain numerical predictions as close as possible to the measured data, in terms of modal frequencies and mode shapes. An evolutionary algorithm [2] is used. After having identified the members potentially subject to fatigue or local vibrations, a substructure finite element model containing the specific member has been studied. The detailed substructure model has been then excited by prescribing at the boundaries the displacement time histories obtained in the corresponding nodes of the global model. From the stresses obtained in the detailed finite element model, the fatigue assessment is carried out following the procedure defined in EN1993 - Eurocode 3 (part 1-9) and the results are compared to those obtained with the procedure proposed in [3]. In order to obtain the stress ranges on each element, dynamic analyses are performed with traffic mixes defined according to EN 1991 - Eurocode 1. Stress range spectra are then determined and the damage indexes are evaluated according to the Miner role.

The article focuses on dynamic identification strategies for complex bridge structures equipped with passive vibration control systems. In detail, a recently built curved twin-deck cable-stayed footbridge was analysed, whose structural complexity required wind tunnel tests and a specific design for vibration reduction. A passive control system was deemed necessary in order to: (i) meet wind safety requirements owing to premature aeroelastic instability, and (ii) mitigate pedestrian vibrations. Uncertainties in numerical modelling and changes during its construction suggested a modal testing campaign in order to check the effectiveness of the vibration absorption system. Different excitation sources related to output-only techniques were exploited, including ambient noise and free-decay oscillations through released masses. Several sensor set-ups were deemed necessary in the view of the structure complexity that exhibits numerous close modes and modal couplings between the two decks. The effect of the dampers was analysed by performing the testing campaign for two distinct configurations: (i) disconnected dampers, and (ii) connected dampers. The dynamic properties of the cables were also investigated in order to complete the whole dynamic characterization of the structure. Two time-domain techniques were applied and compared under different excitations. The dynamic identification procedure provided consistent results and highlighted that full functionality of the damping system was realized only for high vibration levels. Finally, time-frequency instantaneous estimators were applied in order to analyse both the modal frequency and the damping time-variation. These results revealed amplitude dependent behaviours as well as dynamic deck-cable interactions

International audience; — Usually, the joint transmission friction model for robots is composed of a viscous friction force and of a constant dry sliding friction force. However, according to the Coulomb law, the dry friction force depends linearly on the load driven by the transmission, which has to be taken into account for robots working with large variation of the payload or inertial and gravity forces. Moreover, for robots actuating at low velocity, the Stribeck effect must be taken into account. This paper proposes a new inverse dynamic identification model for n degrees of freedom (dof) serial robot, where the dry sliding friction force is a linear function of both the dynamic and the external forces, with a velocity-dependent coefficient. A new sequential identification procedure is carried out. At a first step, the friction model parameters are identified for each joint (1 dof), moving one joint at a time (this step has been validated in [23]). At a second step, these values are fixed in the n dof dynamic model for the identification of all robot inertial and gravity parameters. For the two steps, the identification concatenates all the joint data collected while the robot is tracking planned trajectories with different payloads to get a global least squares estimation of inertial and new friction parameters. An experimental validation is carried out with an industrial 3 dof robot.

In this paper, the latest identification techniques both in the time and in the frequency domains, are applied to the data obtained from the dynamic monitoring of the reinforced concrete tower of the Provincial Administration Building of Bari (Italy). The tower, dating back to the thirties of the 20th century and about 60 m tall, is not only a typical example of the fascist architectural style, but it is an important symbol of the city itself. The extraction of the modal parameters from ambient vibration data has been carried out by using the ARTeMIS Extractor Pro 2010 software. Three different Operational Modal Analysis (OMA) methods have been utilized: EFDD, SSI and Crystal Clear-SSI. The first two couples of bending mode shapes are also estimated and shown.

San Torcato Church is located near the city of Guimarães, Portugal. The construction of the church started in 1871 and completed in recent years. The church combines several architectonic styles, like Classic, Gothic, Renaissance and Romantic. This “hybrid” style is also called in Portugal as “Neo-Manuelino”. At the moment, the church has significant structural problems due to soil settlements of the main façade. Cracks can be observed in the main and lateral facades. The cracks are visible from the outside and inside of the temple. The bell-towers are leaning, and the arches in the main nave present vertical deformations. Non-stabilized phenomena are present in the structure. To stabilize the damage, a structural intervention is planned to occur soon and the church is already monitored to assist the intervention. The paper clearly presents the problem with emphasis to the dynamic analysis carried out before the structural strengthening, namely: the experimental tests with output-only techniques for frequencies, damping and mode shapes estimation, and FE model updating analysis., (undefined)

International audience; Usually, the joint transmission friction model for robots is composed of a viscous friction force and of a constant dry friction force. However, according to the Coulomb law, the dry friction force depends linearly on the load driven by the transmission. It follows that this effect must be taken into account for robots working with large variation of the payload or inertial and gravity forces, and actuated with transmissions as speed reducer, screw-nut or worm gear. This paper proposes a new inverse dynamic identification model for n degrees of freedom (dof) serial robot, where the dry friction force is a linear function of both the dynamic and the external forces. A new identification procedure groups all the joint data collected while the robot is tracking planned trajectories with different payloads to get a global least squares estimation, in one step, of inertial and new friction parameters. An experimental validation is carried out with a 1 dof prismatic joint composed of a Star high precision ball screw drive positioning unit, which allows large and easy variations of the inertial and gravity forces.

This paper deals with the dynamic characterization and the evaluation of the seismic response of the medieval civic tower of Soncino (Cremona, Italy). The dynamic characteristics and the mechanical properties of the masonry tower are evaluated through ambient vibration tests, which provide results in a fast and non destructive way with respect to the traditional methods such as forced vibration tests. Nonlinear static and dynamic analyses are performed on a finite element model of the tower calibrated on the results of the dynamic identification. The damage levels and the seismic capacity of the structure are also evaluated. The obtained results allow to predict the seismic behaviour of the tower and to define possible strengthening and restoration interventions.

An in-depth survey was carried out in situ on the masonry bell tower of the Santa Maria del Carmine Church in the city of Naples, Italy. The analyses followed a multidisciplinary approach to identify its architectural and structural features, to identify the materials used and the state of damage and interventions made in various periods, to assess the stress state in the masonry under gravity loads, and to define its dynamic behavior. The information gathered represents the starting point for designing a seismic upgrade to meet the standards applied to historic monuments.

The Tanaro Bridge, an 18-span 225-m long bridge on the Tanaro River in northwestern Italy, presented the following elements of interest: (1) the barrel divided into adjacent arches; and (2) transverse tie bars and internal spandrels connecting the three parts of the barrels. Its demolition, in 2003, gave the opportunity of performing dynamic tests on a couple of spans at two stages of demolition: (1) fill removed; and (2) fill and internal spandrels removed. Without the uncertain contribution of the fill, some features of the mechanical response of masonry bridges are discussed and the efficiency of tie bars and internal spandrels is addressed. The data provided can be useful for safety assessment procedures.

The paper presents an integrated approach aimed at assessing the seismic safety of Mallorca cathedral. This cathedral is an extraordinary historical construction dating back to the middle-ages. The experimental modal parameters of the cathedral were identified using Ambient Vibration Testing (AVT). The cathedral numerical model was updated using the identified modal parameters. This updated model was then used to study the seismic response of the cathedral using non-linear static (pushover) analysis. A sensitively analysis was carried out to reveal the dependency of the seismic capacity on the input materials properties. To assess the seismic performance and the safety of the cathedral, the N2 method was employed. It was found that the cathedral is safe when subjected to the earthquakes expected in Mallorca Island.