Rocco Ditommaso

Nowadays, Structural Health Monitoring is certainly a topic of great interest both in the research and in the professional field as evidenced by the large number of applications and systems installed all over the world. A permanent monitoring system could be installed in order to identify a possible damage occurred on framed structures after moderate/destructive earthquake. Furthermore, it could be an useful tool for evaluating the service condition and the remaining service life of a structure. Most of simplified methods for structural damage detection are based on the evaluation of the dynamic characteristics evolution associated to the fundamental mode of vibration of a monitored structure. Particularly, the variation of parameters such as eigenfrequencies, equivalent viscous damping factors and modal and/or operational mode shapes has been evaluated and analyzed in order to identify structural damage. Methods based on frequency variation can be applied to detect damage, but they are not able to localize structural damage. Instead, to this aims, methods based on the evolution of modal shapes and/or of their derivatives such as mode curvatures could be more effective. Aim of this work is the improvement of an existing method for damage localization on framed structures based on the evaluation of the mode curvature change associated to the fundamental mode of vibration during an earthquake. The approach is based on the use of a nonlinear filter, the band-variable filter, able to extract the nonlinear response of each mode of vibration. The paper focuses also on the possibility to quantify the damage occurred on the monitored structure by considering the correlation among maximum value of mode curvature variation and the maximum inter-story drift. The regression model between these two parameters has been defined through nonlinear numerical models for different reinforced concrete framed structures designed for gravity loads only, with and without the presence of infill panels.

In this paper two methods of damage localization previously proposed by the authors are combined to smooth the possible drawbacks and boost the advantages each of them. The Modal Interpolation Method (IM), recently proposed, is based on a damage feature defined in terms of the loss of smoothness (that is local increases of curvature) of the modal shapes induced by a local reduction of stiffness. Herein the combination of the IM with the Curvature Evolution Methods (CEM) is proposed. The CEM is based on the use of a Band-Variable Filter able to extract from recorded responses the nonlinear response of one mode of vibration enabling the detection of possible changes of a properly defined damage feature, during a single earthquake. In the CEM the modal curvature is assumed as damage feature. The combination of the two methods CEM and IM is carried out using the Band-Variable Filter to extract the nonlinear response of the structure and assuming as a damage feature the variation of the interpolation error computed at different times during the strong motion. The validation of the combined approach, named Interpolation Evolution Method (IEM), is carried out on a full scale experimental benchmark tested on the UCSD-NEES shake table.

<p>In the last years, existing structures and transport infrastructures, especially those made using reinforced concrete, have experienced significant safety criticalities implying also a relevant social and economic impacts. Structural Health Monitoring techniques represent a reliable response to the problem available to scientists and engineers. A multidisciplinary approach combing knowledge from several research fields and using different kind of technologies would be preferable for this type of application. Most of developed methods for structural damage detection on civil structures and infrastructures is generally based on the evaluation of displacements, eigenfrequencies, damping factors, mode shapes, etc., and their variation over time, by means of on-site installed sensors. In recent years, thanks to the rapid evolution of interferometric SAR processing techniques, a large amount of “satellite measurements” are available for both geophysical phenomena and building monitoring in terms of displacement rate over time. This paper presents an overview on the 2019-2021 WP6 Reluis Project aiming to contribute to the discussion about the opportunity and the modalities to merge information retrieved both by on-site and remote sensing measurements and to define a shared strategy to detect damage on existing structures and infrastructures in operational conditions.</p>

In the last years, there is an increasing attention to the management and monitoring of critical infrastructure with a particular focus on the transport ones. In fact, several infrastructures have experienced (especially bridges) significant safety criticalities, which in few cases led to collapse with significant social and economic impacts. In this context, Structural Health Monitoring (SHM) is necessary in order to provide information, which can support the strategies for increasing the life-time of the structure, correctly planning maintenance interventions, so to ensure safety conditions of the infrastructure under any environmental condition and hazard occurrence. At the sight of the above considerations, at present, significant research efforts are on-going towards development of SHM systems able to get the opportunity of technological advances in sensing and, at the same time, to be economically sustainable. In particular, there is the necessity to design and implement integration strategies, where the modern sensing technologies, coming from several research fields, are combined with the usual tools and models exploited in civil engineering. Therefore, the present contribution deals with a unified approach to the design and development of systems for early warning, monitoring and quick damage assessment of the built environment and critical infrastructures and networks. In this context, the integration is the key factor for exploiting the synergy among different kind of sensing/diagnostics technologies (including new concept of operation, such as the citizen as a sensor and sensors no sensors) and advanced Spatial Data infrastructure and ICT architectures . It is also important to assimilate monitoring data and indicators coming from the sensing into civil engineering; this is crucial to identify actions and strategies for an effective and economically sustainable management of the infrastructure. In addition, the integrated SHM has to be designed and implemented according to several stages exploiting different sensing technologies, which are organized according to a temporal and logical workflow characterized by different levels of observation and knowledge, where the information gained at a level is used to decide whether to activate the next level. At conference, several examples of the proposed integrated SHM approach will be presented, with a focus on transport infrastructure and built environment.

This study presents an innovative strategy for automatic evaluation of the variable fundamental frequency and related damping factor of nonlinear structures during strong motion phases. Most of methods for damage detection are based on the assessment of the variations of the dynamic parameters characterizing the monitored structure. A crucial aspect of these methods is the automatic and accurate estimation of both structural eigen-frequencies and related damping factors also during the nonlinear behaviour. A new method, named STIRF (Short-Time Impulse Response Function - STIRF), based on the nonlinear interferometric analysis combined with the Fourier Transform (FT) here is proposed in order to allow scientists and engineers to characterize frequencies and damping variations of a monitored structure. The STIRF approach helps to overcome some limitation derived from the use of techniques based on simple Fourier Transform. These latter techniques provide good results when the response of the monitored system is stationary, but fails when the system exhibits a non-stationary, time-varying behaviour: even non-stationary input, soil-foundation and/or adjacent structures interaction phenomena can show the inadequacy of classic techniques to analysing the nonlinear and/or non-stationary behaviour of structures. In fact, using this kind of approach it is possible to improve some of the existing methods for the automatic damage detection providing stable results also during the strong motion phase. Results are consistent with those expected if compared with other techniques. The main advantage derived from the use of the proposed approach (STIRF) for Structural Health Monitoring is based on the simplicity of the interpretation of the nonlinear variations of the fundamental frequency and the related equivalent viscous damping factor. The proposed methodology has been tested on both numerical and experimental models also using data retrieved from shaking table tests. Based on the results provided in this study, the methodology seems to be able to evaluate fast variations (over time) of dynamic parameters of a generic reinforced concrete framed structure. Further analyses are necessary to better calibrate the length of the moving time-window (in order to minimize the spurious frequency within each Interferometric Response Function evaluated on both weak and strong motion phases) and to verify the possibility to use the STIRF to analyse the nonlinear behaviour of general systems.

The Fourier transform is certainly one of the main tools used to study the dynamic response of systems. This integral transformation is very useful and reliable if one wants to investigate the response of a stationary system, i.e. a system that doesn't changes its characteristics over time. On the contrary, when the study on the evolution of the dynamic response of a system whose characteristics vary with time is required, the Fourier transform is no longer reliable. In this regard, several mathematical tools to analyze time-variable dynamic responses were developed. Soil and buildings, subject to transient forcing such as an earthquake, may change their characteristics over time with initiation of non-linear phenomena. In most of cases, both for soil and buildings, abandoning the linear elastic field could represent a problem. This paper proposes a new methodology to approach the study of non-stationary response of soil and buildings: a band-variable filter based on the S-Tran...

The demand of a widespread health monitoring of strategic buildings in seismic areas has emphasized the need to realize studies in order to verify the feasibility of economic and fast procedures to detect anomalous vibrations on a large number of buildings, to perform post earthquake monitoring and to define first damage scenarios. Structural health monitoring systems are usually realized with a large number of sensors, suitably distributed on the structure, often involving complex elaborations of big amounts of data. When applied on a large number of buildings these systems can hardly result to be realizable for the necessary long time and the high cost to extract useful information. Within the Italian research RELUIS project, funded by the Italian Department of Civil Protection, a specific task deals with the possibility of applying a fast procedure to determine the damage evolution on a large number of structures after seismic events. The method developed and presented in this pa...

The following paper presents the seismic performance of a two storey post-tensioned Laminated Veneer Lumber (LVL) building during the aftershock sequence following the 6.3 MW 22nd February 2011 Canterbury earthquake. Composed of walls in one direction and frames in the other, the structure under analysis was originally tested quasi-statically in the structural laboratories of the University of Canterbury (UoC), Christchurch, New Zealand. Following testing the building was demounted and reassembled at the offices of the STIC research consortium on the campus of UoC with several significant changes being made to convert the building from its initial use as a test specimen into a functioning office structure. Close to the beginning of construction the 7.1 MW 2011 Darfield earthquake occurred in the Canterbury area however construction went ahead as planned with the building being almost complete when the more devastating 2011 February event occurred. An array of 3 dimensional accelerat...

This work presents the first results obtained by applying in situ and remote-sensing methodologies to monitor the Ponte della Musica-Armando Trovajoli located in Rome, within the activities of the WP6 “Structural Health Monitoring and Satellite Data” 2019-21 Reluis Project. In particular, the use of remote-sensing Differential Synthetic Aperture Radar (SAR) Interferometry (DInSAR) measurements provided a spatial map of the displacement of the investigated infrastructure and the corresponding time-series, with the aim of monitoring deformation phenomena, focusing on the local scale analysis, which produces suitable results for urban monitoring and damage assessment. The DInSAR results have been integrated with the identification of the dynamic characteristics of the bridge, performed through an experimental campaign of ambient vibration measurements carried out in October 2020 and with the local-scale definition of the engineering geological setting of the foundation soil. The subsoi...

In recent years, structural health monitoring (SHM) has received increasing interest from both research and professional engineering communities. This is due to the limitations related to the use of traditional methods based on visual inspection for a rapid and effective assessment of structures and infrastructures when compared with the great potential offered by newly developed automatic systems. Most of these kinds of systems allow the continuous estimation of structural modal properties that are strictly correlated to the mechanical characteristics of the monitored structure. These can change as a result of material deterioration and structural damage related to earthquake shaking. Furthermore, a suitable configuration of a dense sensor network in a real-time monitoring system can allow to detect and localize structural and non-structural damage by comparing the initial and a final state of the structure after a critical event, such as a relevant earthquake. In this paper, the m...

Il ponte sul Basento a Potenza, progettato da Sergio Musmeci e realizzato nel periodo compreso tra il 1969 e il 1972, con la sua ardita struttura costituisce uno straordinario esempio di scultura moderna in calcestruzzo armato, in cui i classici elementi di sostegno verticale (piloni) sono sostituiti da un’unica volta a curvatura variabile che sorregge l’intero impalcato. La particolare forma fa dell’opera un imponente e raffinato oggetto d’arte a scala urbana. L’eta del ponte e il suo continuo ed incessante utilizzo hanno determinato l’esigenza di approfondire la conoscenza del suo grado di sicurezza nei confronti delle sollecitazioni di esercizio (traffico) e di tipo sismico, queste ultime non considerate all’epoca della progettazione della struttura. L’elevata complessita dell’opera in esame ha comportato un’attenta pianificazione delle indagini in situ,mirata al raggiungimento del livello di conoscenza piu elevato possibile. La fase conoscitiva, iniziata con l’analisi della docu...

In this paper, several nonlinear numerical models of reinforced concrete framed structures have been defined in order to evaluate the effects of non-structural elements and soil–structure interaction on the elastic dynamic behaviour of buildings. In the last few years, many and various studies have highlighted the significant effects derived from the interaction between structural and non-structural components on the main dynamic characteristics of a building. Usually, structural and non-structural elements act together, adding both masses and stiffness. The presence of infill panels is generally neglected in the design process of structural elements, although these elements can significantly increase the lateral stiffness of a structure leading to a modification in the dynamic properties. Particularly, at the Damage Limit State (where an elastic behaviour is expected), soil-structure interaction effects and non-structural elements may further affect the elastic natural period of bu...

Damage detection approach based on dynamic monitoring of structural properties over time has received a considerable attention in recent scientific literature. In earthquake engineering field, the recourse to experimental research is necessary to better understand the mechanical behaviour of various structural and non-structural components. Aim of this paper is the optimisation of a methodology based on the evaluation of the mode curvature to detect and localize a possible damage occurred on a framed structure after an earthquake. The methodology is based on the use of accelerometric sensors, one station for each floor, to record accelerometric time-histories and directly evaluate the fundamental mode shape variations from filtered signals. In order to reduce costs and computation, this paper focuses on the possibility to reduce the number of stations installed on the monitored structures. In this study, the attention has been concentred to minimize the number of sensors, as a funct...