Papers by Keyword: Damage Detection

Abstract: In this paper the IDDM (Interpolation Damage Detection Method), recently proposed as a speedy damage detection and localization technique, is applied to the numerical model of a cable suspended bridge derived from the ANSYS model of the Shimotsui-Seto Bridge in Japan (940m length of the main span). The wind excitation is simulated as a spatially correlated process acting in the horizontal direction, transversal to the deck. The bridge is assumed to be monitored by sensors located at the nodes of the model along the longitudinal axis, and recording the absolute acceleration of the bridge deck in the transversal direction Noise in recorded responses can reduce the sensitivity of the method to damage. The influence of noise on the results of the damage detection method is herein investigated by adding a white-noise signal to the structural responses. The mutual relationship between level of noise, intensity of damage and lengths of recorded signals is also investigated with reference to various damage scenarios.

Abstract: Fiber optic sensors become very popular for structural testing and monitoring in civil engineering nowadays, due to its advantage of high resolution and environment durability. In this paper, long-gauge fiber optic bragg grating sensors will be introduced. Structural damage detection stratagem using the micro-strain mode will be studied. Then its application to a structural testing and monitoring for a real long span truss bridge will be discussed in detail. In the testing, 23 long-gauge fiber optic bragg grating sensors were deployed on the mid span of the bridge. Testing were made under conditions either there is train on the bridge or no train on it. Corresponding dynamic characteristics were analyzed and discussed. Results of the testing show that long-gauge fiber optic sensors can work well for structural testing and also damage detection for truss bridges.

Abstract: Structural damage identification is basically a nonlinear phenomenon; however, nonlinearprocedures are not used currently in practical applications due to the complexity and difficulty forimplementation of such techniques. Therefore, the development of techniques that consider the nonlinearbehavior of structures for damage detection is a research of major importance since nonlineardynamical effects can be erroneously treated as damage in the structure by classical metrics. Thispaper proposes the discrete-time Volterra series for modeling the nonlinear convolution between theinput and output signals in a benchmark nonlinear system. The prediction error of the model in anunknown structural condition is compared with the values of the reference structure in healthy conditionfor evaluating the method of damage detection. Since the Volterra series separate the responseof the system in linear and nonlinear contributions, these indexes are used to show the importanceof considering the nonlinear behavior of the structure. The paper concludes pointing out the mainadvantages and drawbacks of this damage detection methodology.

Abstract: Modal filtration in the field of damage detection has many advantages, including: its autonomous operation (without the interaction of qualified staff), low computational cost and low sensitivity to changes in external conditions. However, the main drawback of this group of damage detection methods is its limited applicability to operational data. The modal filtration of the responses spectra (in place of FRFs), proposed in the literature, often does not give the expected results, working properly only for excitation in the form of white noise, or an ideal impulse. In other cases, for example in rotational machines, when in the response spectrum the rotational velocity harmonics dominate it can give wrong results. For such cases authors propose to use a new type of spatial filter, similar to modal filter with the difference that it has ability to filter the operational deflection shape components from the system response. Its application together with classical modal filter allows for damage detection using operational data with other type of excitation. The main assumption of the new spatial filter is the orthogonality of the filter coefficient vector to the operational deflection shape vector, it is then similar to the classical modal filter.

Abstract: This paper investigates the use of Moving Force Identification as a method of bridge damage detection. It identifies changes in the predicted axle force histories that occur as a result of loss in bridge element stiffness, i.e. as a result of bridge damage. A 2-dimensional Vehicle-Bridge Interaction model is used in numerical simulations to assess the effectiveness of the method in detecting changes in stiffness. Fleets of similar vehicles are simulated and the mean force pattern is used as the damage indicator. Results show that the method is more sensitive to damage than direct measurements of displacement. The paper also explores the use of the force history as an indicator of damage location.

Abstract: Weigh-In-Motion (WIM) and Bridge Weigh-In-Motion (B-WIM) are systems that allow obtaining the axle weights of road vehicles in motion, at normal traffic speeds. While WIM employs sensors embedded in the road pavement, B-WIM use the strain recordings of a bridge to infer the traversing vehicle axle weights. Both systems have been heavily improved over the past decades, and commercial versions are currently in operation. The two main applications of these systems are: (1) to assess the traffic loading on the infrastructure, and (2) to enforce the maximum weight limits. This paper suggests a novel application of these two systems to identify changes in bridge stiffness. It requires the bridge to be instrumented with a B-WIM system and a WIM system nearby. The principle is to use both systems to evaluate the gross weight of vehicles passing over the bridge and correlate their predictions. Changes in correlation of the predicted axle weights over time will indicate either structural damage or faulty sensor. A finite element model of a coupled vehicle-bridge system with different damage scenarios is used to test the approach numerically. Vehicle mechanical properties and speeds are randomly sampled within a Monte Carlo simulation. Results show how correlation changes as damage increases and how this correlation can be employed as a damage indicator.

Abstract: The paper consists of two parts. First, Electromechanical Impedance (EMI) method is proven to be able to determine some vibrational characteristics of the investigated structure. In order to verify this statement, Scannig Laser Vibrometry (SLV) is used to correlate frequency peaks of velocity (or displacement) operational deflection shapes with corresponding ones obtained by EMI method. Finally, the influence of moisture content in CFRP sample on resonance peaks is investigated using EMI method. Damage detection indicator in this case is based on shifts of resonant peaks.

Abstract: In this paper, the possibility and validity of damage detection based on velocity response of a simply supported beam under the moving load are examined theoretically and numerically. It includes the following parts: First, the theoretic background of the beam vibration subjecting to moving load is briefly described. And then, the velocity responses of a simple supported beam are calculated by software Ansys. Using wavelet transform, the damage location can be identified successfully. At last, the effects of noise and load speed are discussed in detail. Numerical studies show the validity of the proposed method and a good noise tolerance using the velocity response.

Abstract: This work constitutes a damage detection study of a glass plate using the statistical approach of outlier analysis, which is also referred to here as novelty detection. A glass plate instrumented with low-profile, surface-bonded transducers is used in the investigation. Ultrasonic Lamb waves are applied for detecting various crack length on the same plate. The study reveals a distinction between the damage and undamaged plate, and also assesses the severity of damage.

Abstract: This paper applies a methodology for damage detection in beams proposed by the authors. The methodology is based on a continuous wavelet analysis of the difference of mode shapes between a damaged state and a reference state. The wavelet transform is used to detect changes in the mode shapes induced by damage. The wavelet coefficients for each mode are added up and normalized to unity in order to obtain a clear and precise damage assessment. A curve fitting approach reduces the effect of experimental noise in the mode shapes. When only a small number of measuring points are available, a cubic spline interpolation technique provides additional “virtual” measuring points. The interpolation technique may also be used when measuring points are not equally spaced. It also serves as a softening technique of the mode shapes when applied, and no curve fitting approach is used in that case. An antisymmetric extension at both ends of the mode shapes is used to avoid the edge effect in the wavelet transform. The paper presents the results obtained for steel beams with an induced crack. Several sizes and locations of the crack have been considered. The paper addresses several issues affecting the accuracy of the proposed methodology, such as the number of measuring points and the effect of the extension, curve fitting and interpolation techniques.