This paper presented an experimental study on piezoelectric impedance based cubic and axial compressive strength gain
monitoring in concrete during curing process. The piezoceramic (PZT) patch was attached on the concrete specimen to
collect the monitoring signal. The electro-mechanical impedance (EMI) spectra of surface bonded PZT patch were
collected using an impedance analyzer by sweeping the frequency. A regression analysis is conducted to establish the
empirical relationship between the relative strength gain of concrete and the monitored relative resonant frequency
change of the EMI spectra. The established empirical formula is used for concrete strength monitoring via EMI spectra.
The results tell that the EMI technique is a practical and reliable nondestructive test method for concrete strength gain
This paper presents a numerical simulation study on electromechanical impedance technique for structural damage
identification. The basic principle of impedance based damage detection is structural impedance will vary with the
occurrence and development of structural damage, which can be measured from electromechanical admittance curves
acquired from PZT patches. Therefore, structure damage can be identified from the electromechanical admittance
measurements. In this study, a model based method that can identify both location and severity of structural damage
through the minimization of the deviations between structural impedance curves and numerically computed response is
developed. The numerical model is set up using the spectral element method, which is promised to be of high numerical
efficiency and computational accuracy in the high frequency range. An optimization procedure is then formulated to
estimate the property change of structural elements from the electric admittance measurement of PZT patches. A case
study on a pin-pin bar is conducted to investigate the feasibility of the proposed method. The results show that the
presented method can accurately identify bar damage location and severity even when the measurements are polluted by
Proc. SPIE. 7292, Sensors and Smart Structures Technologies for Civil, Mechanical, and Aerospace Systems 2009
KEYWORDS: Principal component analysis, Image processing, Video, Distortion, Photogrammetry, Finite element methods, System identification, Digital video recorders, Structural dynamics, 3D image processing
In this paper, a non-contact dynamic displacement measurement method based on video motion detection (VMD)
technique and a structural modal identification technique based on the principal component analysis (PCA) is proposed
for vibration tests and modal identification of frame structures. Relying on the instant digitized image acquiring using a
digital video recorder and image processing based on the close-range photogrammetry theory, the dynamic deformation
of a structure can be measured. The PCA is then employed to decompose the correlated structural deformation
measurements into statistically uncorrelated ones. Under the condition of small damping, these uncorrelated data can be
shown to be related to modal responses and can be used to estimate the modal parameters of a structure. To demo the
process and validate its accuracy, a dynamic test on a scaled frame structure is conducted in the lab. Dynamic responses
at given target point were obtained and structural modal parameters were estimated. Compared with the modal
parameters obtained from the eigenvalue analysis of a FEM model, the proposed method is of enough precision for
vibration tests and modal identification of frame structures.
Recent disease surveys on some cable-supported bridges show that cable corrosion is one of the main dangers for bridge safety, serviceability and durability. Since cables are the main supporting components for these bridges, this type of damage must be detected at the earliest possible stage for further maintenance. Acoustic monitoring technique shows an efficient way for this purpose. This paper presents such a research on modeling and wavelet analyzing the acoustic emission signal in seven-wire strands for damage diagnosis. In order to demonstrate the accuracy of the proposed technique, the propagation of the guided waves in a cylindrical bar is examined firstly. These modeling results are compared to some analytical results. The comparisons clearly illustrate the effectiveness of the guided wave propagation modeling technique and verify the potential of the modeling technique on solving those problems whose analytical solution is not available due to the complexity of the component geometry. The modeling technique is then used to generate the wave samples for two damage conditions of the seven-wire strands and a wavelet based pattern extraction technique is adopted to extract the baseline time-frequency characteristics of the wave.
Thanking to its distinguishing advantages including wavelength multiplexing capability, miniature size, high sensitivity, immunity from electro-magnetic interference and etc, the fiber Bragg grating (FBG) sensing technologies are regarded as a competent candidate for the bridge long-term health monitoring. According to the shifted Bragg wavelength of the light reflected by a fiber grating, the FBG sensors can accurately measure various physical properties such as strain, temperature, displacement, acceleration and corrosion. One special advantage of the FBG sensing technology is that only one demodulation device is required to acquire various physical properties simultaneously. Compared with the bridge health monitoring system using conventional sensors, this advantage makes the quasi-distributed sensing possible and data transmission more convenient because many FBG sensors can be connected in series by a single fiber. In this paper, an integrated FBG sensing system is presented for monitoring the physical state of a real bridge, the main-navigation channel cable-stayed bridge of the Donghai Bridge. The strain variation of two selected sections in the construction stage and during the load trial test are continuously monitored. The results of this study will supply a good guidance for the use of FBG sensors on the health monitoring of real bridges. Finally, the paper present the design and fabrication of an accelerometer based on the FBG technology for structure vibration monitoring.
Most structural responses can be considered as the superposition of some monotonic components. These monotonic components contain modal information that can be used for structural damage detection and health monitoring. This paper presents a comparative study of three techniques for signal decomposition and analysis. These techniques are the wavelet transform (WT) technique, the empirical mode decomposition (EMD) technique, and the principle component analysis (PCA) technique. These techniques are all capable of decomposing multi-component signals into a summation of mono-components without resorting to the traditional frequency-domain approach. All three techniques can estimate natural frequencies, damping ratios and mode shapes of a structure from its time-domain vibration responses and hence can be used to monitor structural condition. A numerical study on a three-story shear-beam building frame is performed and presented to show the accuracy of these techniques.
In this study, a technique that integrates the wavelet transform with a covariance-driven modal analysis scheme, is proposed to address the output-only modal analysis problem. Under the assumption that the ambient excitation can be modeled as a white-noise process, the output covariance is computed firstly to separate the effect of random excitation from the response measurement. The wavelet transform is then employed to convert the covariance vector in the time domain to the power scalogram in the time-scale plane. The wavelet coefficients along the energy concentrated curve are extracted and the structural modal parameters including the resonant frequency, modal damping and mode shape vector can then be estimated based on the amplitude and the phase of the extracted wavelet coefficients. As the wavelet transform has a capacity to capture both stationary and transient information from the original measurement, the proposed technique provides a promising approach for identifying modal properties of both linear and nonlinear structures. Both numerical and experimental studies are performed to demonstrate the proposed technique and verify its accuracy. The results show the proposed method works very well in identifying modal parameters of structures with multiple degrees of freedom.
A novel structural damage assessment technique based on the principal component analysis (PCA) and the flexibility matrix approach is proposed in this paper. The technique is a model free method and can be used for detecting damage occurrence and location. The PCA is adopted firstly to decompose a set of correlated structural response measurements into statistically uncorrelated ones. Under the condition of small damping, these uncorrelated data can be shown to be related to modal responses and can be used to estimate the modal properties of a structure. The structural flexibility matrix can then be constructed using the estimated modal parameters. The change in the flexibility matrix gives an indication of the occurrence and location of structural damage. A numerical study on a 7-storey shear beam building model is performed to illustrate the applicability of the proposed technique. The results show that the proposed technique can accurately identify the occurrence and location of structural damage when the building is subjected to various earthquake excitations.
The use of dynamic response to identify damage location and extent of civil engineering structures has been an increasing research focus in recent years. Most of the vibration-based damage assessment methods developed till now require modal properties that are obtained via the traditional Fourier transform. Unfortunately, these Fourier-based modal properties, such as natural frequencies, mode shapes, etc., have been reported to be insensitive to structural damage and hence are not regarded as good damage indicators. In this paper, a novel structural condition index, wavelet packet signature (WPS), is proposed for locating and quantifying structure damage. After extracting the WPS from the response measured at various locations, the spatial distribution curvature of the WPS is used for locating damage. A numerical study on a simply supported beam shows that, according to the difference of the spatial WPS distribution curvature, the damage position can be accurately located and the damage severity can be qualitatively assessed. One special advantage of the proposed method is it does not require an accurate analytical model of the structure been monitored and is very suitable for practical application.
In this paper, study on a new 0-3 type cement-based PZT (Lead Zirconate Titanate) composities is presented. Using a normal mixing and compacting method, up to 50vol% PZT ceramic powder could be incorporated into cement-based composites. The behaviors of the composites under different polarizing conditions are investigated. And the piezoelectric properties of cement-based PZT composites are evaluated both theoretically and experimentally. Moreoever, the impedence spectrum of composites is studied to approve the electromechanical coupling behavior. It shows that cement-based PZT composities have some advantage to the polyer-based PZT composites. There is good potential for application of 0-3 type cement-based piezoelectric composites in civil engineering.
Wavelets analysis is a mathematical tool that can represent a signal in terms of a set of basis functions and thus can describe the signal on various levels of resolutions or scales corresponding to different frequency bands. They have advantages over traditional Fourier methods in analyzing nonstationary signal. In this study, a method based on wavelet packet decomposition (WPD) is proposed to process vibration signals of a structure that undergoes characteristic changes due to damage. The method decomposes the vibration signals into a data set with various levels of resolutions, hence small changes caused by structural damage become visible in some levels. The wavelet packets are used since they can produce narrower and more improved frequency resolutions as compared to the original wavelet. Based on this decomposition, component energy indices are chosen as indicators for structure health condition assessment. For illustration, a numerical simulation is performed on a three-span continuous bridge deck with different characteristic changes under impact loads. The case study shows that the component energy indices obtained from the WPD are excellent indicators for structure health condition assessment. When they are fed into well-trained neural network classifiers, structural conditions such as damage occurrence, location and severity can be identified quite accurately.