1,721,044 research outputs found
On the estimation of the fundamental modal properties of Italian historical masonry towers
No full textThe preservation of historical structures is a very challenging problem that requires strong interdisciplinary efforts, in particular in those countries where seismic risk is relevant and the integration between conservation and protection can be very difficult. Recent Italian earthquakes hit many valuable masonry structures marking the urban and rural landscape. Among those, masonry towers are often impressive signs of past cultures and folks. Non-destructive testing of such structures has been widely investigated and discussed in the technical literature. In the present paper, some aspects related to output-only modal identification of tower-like masonry structures for their non-destructive characterization in view of seismic performance assessment are discussed. Specific attention is paid to the role of Operational Modal Analysis in the seismic analysis of masonry towers and the development of empirical predictive correlations
Structural Health Monitoring through automated OMA techniques in operation and during seismic events
No full textIntegrated seismic early warning and structural health monitoring of critical civil infrastructures in seismically prone areas
No full textA large part of Europe is exposed to medium/high seismic risk. Throughout the past decades serious structural damage and collapse have occurred in different countries. Examples of structures at risk are existing infrastructure and public buildings. Efficient seismic protection is especially required in these structures. In fact, an earthquake can lead to a high number of injury or death since these structures are often crowded. On the other hand, strategic structures have to be fully operational to manage the aftershock emergencies. This article deals with some results of a research focused on the development of optimized structural health monitoring (SHM) technologies and data processing techniques for critical structures in seismically prone areas. Specific solutions are proposed to take advantage of seismic early warning systems (SEWSs), which are becoming very popular and effective worldwide. The most relevant aspects of seismic early warning (SEW) and SHM systems are herein reviewed and the main issues related to their integration are discussed in order to properly design the final system. Attention is mainly focused on dynamic behavior in operational conditions and on earthquake effects. Hardware and software solutions adopted for the characterization and monitoring of the dynamic response of a sample building are illustrated pointing out the capability of the same architecture to host data and information provided by SEW applications. Finally, datasets in operational conditions are used to evaluate the fundamental modal parameters of the structure by output-only techniques, whose potentialities and limitations in the presence of weakly and heavily nonstationary signals have been also assessed. In particular, they have been applied, respectively, to the records collected during crowded football matches hosted at the stadium located nearby the sample building and during the recent L’Aquila earthquake mainshock
An approach to automated modal parameter identification for Structural Health Monitoring applications
No full textStructural Health Monitoring is an emerging technology in civil engineering. Several worldwide applications are reported in the literature and several methods able to assess the health state of a structure exist. Some techniques aim at tracking changes in structural response directly or indirectly related to the mechanical characteristics (natural frequencies, etc.) during service life and especially after damage due to exceptional loads. Alternative approaches are focused on postprocessing of measurement data to detect anomalies. In both cases, the trend is to develop methods able to automate detection process exploiting recent advances in information technologies (IT). As the first group of techniques is considered, one of the most relevant drawbacks is represented by the need of a user intervention during the structural modal parameters identification process. This specific aspect does not fulfil the requirements of SHM systems, which should be fully automated, in particular when several structures are monitored at the same time and distributed damage is expected, like in seismic regions. In the present paper, a proposal for automated modal parameters identification and tracking is reported. The algorithm herein described is set to tackle the above described drawbacks and can be integrated in a fully automated SHM system. The algorithm is under development in a LabView environment software program. It is based on a well-known technique of operational modal analysis, the so-called Frequency Domain Decomposition, in both cases of blind identification and tracking of modal parameters. In particular, the paper is basically focused on the first issue and on the link between this procedure and the other one for automated modal parameters tracking, pointing out the opportunities offered by such a system for performance evaluation. Finally, applications to a simulated and a real case study will be discussed, in order to identify potentialities and limits of the proposed solution. © Civil-Comp Press, 2008
Some remarks on experimental estimation of damping for seismic design of civil constructions
No full textExperimental estimation of damping is currently not a comprehensively solved problem. Although modal frequencies and mode shapes can be measured confidently and quite easily by means of dynamic tests on civil structures, an accurate identification of damping ratios needs further development. Experimental values can be characterized by large error bounds mainly because damping is strongly influenced by the magnitude of the dynamic response of a structure.
In this paper, the main issues concerning identification of modal damping ratios are discussed in order to define methods for their reliable estimation, to reduce uncertainties and characterize error bounds. According to this aim, a procedure for optimized modal parameter estimation via Stochastic Subspace Identification is also proposed. Then data collected from an extensive literature review are analyzed depending on the type of structure in order to point out the main factors affecting damping. Moreover, a comparison with provisions about structural damping given in National and International seismic codes for structural design of civil structures is reported. This process demonstrates that the development of a damping database based on homogeneous and reliable estimates is required for calibration of predictive formulations to be used in the framework of performance-based seismic design
Fully automated OMA: An opportunity for smart SHM systems
No full textAdvances in dynamic identification procedures and optimization of hardware performances play a relevant role in the development of Structural Health Monitoring in hazardous areas. Several worldwide applications are reported in the literature and several methods able to assess the health state of a structure exist, some of which are based on tracking the modal characteristics of the structure during service life and especially after damage due to exceptional loads. The most relevant drawbacks of such methods, however, is represented by the need of a user intervention during the modal parameter identification processes, that does not fit requirements of SHM systems. In this paper, an approach for automated modal parameters identification and tracking is described: the algorithm has been integrated in a fully automated SHM system and is based on a consolidated technique of operational modal analysis, the Frequency Domain Decomposition. The algorithm has been implemented into a specific software package developed in LabView 8 environment and it is still submitted to extensive tests. Some results obtained since its integration in the SHM system of the School of Engineering Main Building at University of Naples are reported and the potentialities of such algorithm as engine of smart SHM system are described. © 2009 Society for Experimental Mechanics Inc
Operational modal analysis and earthquake engineering
No full textOperational Modal Analysis (OMA) techniques are powerful and versatile and applications in technical literature are becoming frequent. In the present paper a number of case studies will be reviewed in order to point out the effectiveness of such procedures in the earthquake engineering area. Assessment of seismic performance of structures and characterization of their dynamic behaviour in operational conditions will be analyzed and the interaction between experimental tests and finite element modelling will be discussed. Moreover, attention will be focused on the role of modal parameter identification for damage assessment of structures. Potential of output-only technique in the field of Structural Health Monitoring (SHM) and damage assessment of structures will be discussed and its actual integration within fully automated SHM systems will be described
An automated procedure for modal parameter identification of structures under operational conditions
No full textStructural Health Monitoring are frequently reported in the literature and a number of techniques exist for the assessment of the health state of a structure. Some of them aim at tracking changes in structural response directly or indirectly related to the mechanical characteristics (such as natural frequencies, etc.) of the structure before and after damage. Conversely, other procedures are based on the post-processing of measurement data to detect anomalies from measurements (ARMAV modeling, wavelet decomposition, etc.). In both cases, the trend is in using methods able to automate the detection process by taking advantage of the recent advances in information technologies. Considering the first group of techniques, one of the main drawbacks is related to the need of a user intervention in order to identify the modal parameters of the structure. This aspect does not fulfill the requirements of SHM system, which should be fully automated, in particular when several structures are monitored at the same time and a post-earthquake scenario is required. In the present paper, a procedure, implemented in LabView environment and able to overcome some typical drawbacks of classical operational modal analysis, is described. Such software can work as a stand alone application, based on previously recorded data or on data obtained during test from a data acquisition hardware, or as a part of a fully automated Structural Health Monitoring system. The algorithm and the software are briefly discussed and a number of case studies are reported, pointing out potentialities and limits of the proposed procedure in identifying the modal parameters of different typologies of structures (moment resisting r.c. frames, masonry bell tower, tuff vault, and so on). Data come from all previously mentioned sources and a specific case study, related to the integration of the software into fully automated SHM systems, will be analyzed. © Institute of Materials Engineering Australasia Ltd
Automated modal identification for Structural Health Monitoring: A critical assessment
No full textAdvances in dynamic identification procedures and optimization of hardware performances play a relevant role in the development of Structural Health Monitoring in hazardous areas. Several worldwide applications are reported in the literature and several methods able to assess the health state of a structure exist. Some of these techniques aim at tracking changes in structural response directly or indirectly related to the mechanical characteristics (natural frequencies, etc.) during service life and especially after damage due to exceptional loads. One of the most relevant drawbacks of such methods is represented by the need of a user intervention during the structural modal parameter identification processes. This specific aspect does not fully fit requirements of SHM systems, which should be fully automated. In order to overcome this limitation, a number of algorithms have been proposed in recent years. In this paper, after a comprehensive literature review, a critical assessment of the available automated modal identification procedures will be carried out, pointing out advantages and limitations of each method. Finally, the main aspects of an automated FDD-based modal identification algorithm will be described and some sample case studies will be discussed in order to point out its effectiveness. The algorithm has been implemented into a specific software package, named LEONIDA, developed in LabView environment. Some peculiar aspects of software implementation will be shortly reviewed and some issues related to the integration within a fully automated Structural Health Monitoring system will be analyzed
Modal Identification of a CDW-Based Structure
No full textConstruction and demolition waste (CDW) arises from activities such as construction, maintenance, partial or total demolition of buildings and civil infrastructures. It consists of heterogeneous materials with high potential for recycling and re-use. For this reason, innovative technologies are being developed to produce prefabricated elements, for both structural and non-structural applications, with high degree of CDW recycled materials. The present paper deals with numerical and experimental investigations performed on a CDW-based structure. A Finite Element Model of the experimental mock-up is assembled to numerically predict its modal properties. Considering that the overall performance of structural assemblies with CDW-based components depends on the performance of mutual connections between precast components, output-only modal identification tests have been carried out to validate the numerical model. Moreover, an experimental campaign was performed by means of shaking table tests, using acceleration time histories according to AC156 requirements, with increasing intensity level. Natural frequencies and corresponding mode shapes have been estimated at each loading step to investigate the effect of increasing structural damage on the dynamic properties of the structure
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