Chapter Electromagnetic Sensing Techniques for Non-Destructive Diagnosis of Civil Engineering Structures

Environmental policy & protocol

Electromagnetic Sensing Techniques for Non-Destructive Diagnosis of Civil Engineering Structures

Environmental policy & protocol

Advanced Video-Based Processing for Low-Cost Damage Assessment of Buildings under Seismic Loading in Shaking Table Tests

This paper explores the potential of a low-cost, advanced video-based technique for the assessment of structural damage to buildings caused by seismic loading. A low-cost, high-speed video camera was utilized for the motion magnification processing of footage of a two-story reinforcedconcrete frame building subjected to shaking table tests. The damage after seismic loading was estimated by analyzing the dynamic behavior (i.e., modal parameters) and the structural deformations of the building in magnified videos. The results using the motion magnification procedure were compared for validation of the method of the damage assessment obtained through analyses of conventional accelerometric sensors and high-precision optical markers tracked using a passive 3D motion capture system. In addition, 3D laser scanning to obtain an accurate survey of the building geometry before and after the seismic tests was carried out. In particular, accelerometric recordings were also processed and analyzed using several stationary and nonstationary signal processing techniques with the aim of analyzing the linear behavior of the undamaged structure and the nonlinear structural behavior during damaging shaking table tests. The proposed procedure based on the analysis of magnified videos provided an accurate estimate of the main modal frequency and the damage location through the analysis of the modal shapes, which were confirmed using advanced analyses of the accelerometric data. Consequently, the main novelty of the study was the highlighting of a simple procedure with high potential for the extraction and analysis of modal parameters, with a special focus on the analysis of the modal shape’s curvature, which provides accurate information on the location of the damage in a structure, while using a noncontact and low-cost method

Identifying Damage in Structures: Definition of Thresholds to Minimize False Alarms in SHM Systems

In recent years, the development of quick and streamlined methods for the detection and localization of structural damage has been achieved by analysing key dynamic parameters before and after significant events or as a result of aging. Many Structural Health Monitoring (SHM) systems rely on the relationship between occurred damage and variations in eigenfrequencies. While it is acknowledged that damage can affect eigenfrequencies, the reverse is not necessarily true, particularly for minor frequency variations. Thus, reducing false positives is essential for the effectiveness of SHM systems. The aim of this paper is to identify scenarios where observed changes in eigenfrequencies are not caused by structural damage, but rather by non-stationary combinations of input and system response (e.g., wind effects, traffic vibrations), or by stochastic variations in mass, damping, and stiffness (e.g., environmental variations). To achieve this, statistical variations of thresholds were established to separate linear non-stationary behaviour from nonlinear structural behaviour. The Duffing oscillator was employed in this study to perform various nonlinear analyses via Monte Carlo simulations

Automatic evaluation of the fundamental frequency variations and related damping factor of reinforced concrete framed structures using the Short Time Impulse Response Function (STIRF)

Structural Health Monitoring (SHM) aims to improve knowledge of the safety and maintainability of civil structures and infrastructures. This paper presents an innovative strategy for automatic evaluation of the variable fundamental frequency and related damping factors of nonlinear structures during strong motion phases. In fact, most of methods for damage detection are based on the assessment of the variations related to dynamic parameters characterizing the monitored structure. In this case, a crucial aspect is a correct estimation of both structural eigenfrequencies and related damping factor also during the nonlinear behavior of a monitored structure. In this paper, nonlinear interferometric analyses combined with the Fourier Transform (FT) are proposed to evaluate the Short-Time Impulse Response Function (STIRF) able to characterize frequencies and damping variations of a monitored structure. Two application of the STIRF are proposed on both numerical and experimental models

Short Time Impulse Response Function (STIRF) for automatic evaluation of the variation of the dynamic parameters for reinforced concrete framed structures during strong earthquakes.

This study presents an innovative strategy for automatic evaluation of the variable fundamental frequency and related damping factors 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 based on the nonlinear interferometric analysis combined with the Fourier Transform (FT) (Short-Time Impulse Response Function - STIRF) is here proposed in order 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

Short Time Impulse Response Function (STIRF): an operative tool for the automatic evaluation of the main eigenfrequencies of structures subjected to relevant earthquakes

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

Advanced Research in Seismic Resilience of Structures and Infrastructures

Dear Colleagues, In recent years, several countries have experienced heavy damages produced by earthquakes on existing structures designed considering only gravity loads. In some cases, new structures designed according to recent international seismic codes have also exhibited inadequate levels of seismic performance, especially in terms of serviceability limit state. Moreover, most economic loss associated to earthquakes is often strongly correlated to damage of nonstructural elements. As structural vulnerability contributes to raising the seismic risk, a comprehensive model to quantify seismic resilience of structures is needed in order to estimate the capacity of integrated systems to rebound after severe earthquakes. This Special Issue aims to collect high-quality papers on advanced research on seismic resilience of structures and infrastructures (including buildings, bridges, cultural heritage, strategic life lines, etc.) dealing with different topics. In particular, recent research on seismic input definition, influence of dynamic soil–structure interaction, structural retrofit, passive control of structures, structural health monitoring, damage detection, and new structural systems toward earthquake-resilient structures is welcome for this interdisciplinary Special Issue. Prof. Dr. Felice Carlo Ponzo Dr. Antonio Di Cesare Dr. Rocco Ditommaso Guest Editor