Papers by Keyword: Damage Detection

Abstract: This paper presents a two-stage method for damage identification in cantilever beam structures using the incomplete measured static and dynamic paramenters. The first stage locates damages preliminary by using the static displacement changes, which is obtained by the static test of structure. It has been shown that the point from which the static displacement difference starts increasing linearly is the location of damage. After the suspected damaged elements are determined in the first stage, the first order sensitivity of the structural natural frequency is used to identify damages more precise in the second stage. The significant advantage of the proposed method is that it is economical in computation and is simple to implement. A cantilever beam structure is analyzed as a numerical example to verify the present method. Results show that the proposed method performs well even if the measurement errors inevitably make the damage assessment more difficult. It has been shown that the presented two-stage methodology may be a promising tool to be used by research groups working on experimental damage detection.

Abstract: A new kind of embedded acoustic emission (AE) sensor has been developed and it was made up of 1-3 cement-based piezoelectric composites. Compared with those sensors which were traditionally affixed to concrete structures, the embedded AE sensors could minimize the leakage of AE hits and improve the accuracy of data acquisition. The AE thresholds of the sensors are 45dB and they can perceive the position of source and crack extending areas in concrete. Because of the low operation cost, the admirable compatibility with concrete and the excellent durability, the sensors could be widely used in the monitoring of civil structure.

Abstract: A new method of measurement of the cable force in cable-stayed bridge model test is introduced. Pressure ring sensor is used as the main component in this method and the tension of the stay cables can be measured real-time and in time. It is vertified that this method is exact and credible by model test and can be used in actual cable-stayed bridge. The static measurements for the test model are conducted. The testing results are compared with the numerical results of finite element model developed for the test model. A platform is established for the future researchs.

Abstract: Structural damage detection using vibration modes has become a very important research area in recent years. In this paper, an improved generalized flexibility sensitivity method is presented for structural damage identification. The existing generalized flexibility method is firstly reviewed and then an improved technique is proposed. In this contribution, a simple accelerated formula is developed to improve the accuracy of the generalized flexibility method. With the introduction of the accelerated formula, the proposed method is able to achieve more accurate results than that obtained by the original generalized flexibility method without any high-order analysis or multi-iterations. The effectiveness of the proposed method is illustrated using simulated data on a published numerical example. From the numerical results, it can be conclued that the proposed new method is very efficient with only the first frequency and its corresponding mode shape. It has been shown that the proposed procedure is simple to implement and may be useful for structural damage identification.

Abstract: Damage of shear connectors in slab-on-girder structures will result in shear slippage between slab and girder, which significantly reduces the load-carrying capacity of the bridge. This paper proposes a dynamic damage detection approach to identify the damage of shear connectors in slab-on-girder bridges with power spectral density transmissibility (PSDT). PSDT formulates the relationship between the auto-spectral density functions of two responses. Measured impact force and acceleration responses from hammer tests are analyzed to obtain the frequency response functions at the slab and girder sensor locations by experimental modal analysis. When measurement data from the undamaged structure are available, PSDT from the slab response to the girder response is derived with the obtained frequency response functions. PSDT matrices in the undamaged and damaged states are directly compared to identify the damage of shear connectors. When the measurement data from the undamaged structure are not available, PSDT matrices from measured response at a reference sensor response to those of the slab and girder in the damaged state can also be used to detect the damage of shear connectors. Experimental studies with a concrete slab supported by two steel girders are conducted to investigate the accuracy and efficiency of the proposed approach. Identification results demonstrated that damage of shear connectors can be identified accurately and efficiently with and without measurement data from the undamaged structure.

Abstract: The flexibility can be approximately synthesized with the first several measured modal parameters, i.e. the so called modal flexibility. The modal flexibility matrix will change with damage in a structure, and the change of modal flexibility should contain the information of damage. It is important to find a damage index that can pick up damage from the change of modal flexibility. To address this issue, the mathematical tool LU decomposition is introduced to deal with the modal flexibility matrix in order to find damage clearly. After decomposition, the modal flexibility is decomposed into a lower triangular matrix L and an upper triangular matrix U. Numerical results of both single and multiple damage cases under white noise excitation indicate that the matrix U has enough information of damage; and the proposed new technique can be utilized to locate the damage accurately. The present numerical study will lay a foundation for the application of real-time structural health monitoring in experiments and engineering.

Abstract: Belt conveyors are one of the most popular methods of material transport in many branches of industry, especially in mining. The average length of mining belt conveyor is about 1000 m. Taking into account that total length of transportation ways in averaged mine can approach several dozen of kilometers and network of several conveyors may cover large area, maintenance of such specific transportation system is very difficult. In this work we propose an automatic multi-channel system for data acquisition and processing for damage detection in belts. Belts with steel cords are considered here, they consist of top and bottom rubber covers and steel cords in between them. Due to many reasons (mainly sharpness of transported materials) covers may be damaged and it may initiate degradation process or straight damages in steel cords. Properties of steel cords are therefore crucial for overall strength of belts, if they are damaged, it may cause catastrophic failure of the whole conveyor. So, monitoring of belts conditions is a crucial issue. We proposed a monitoring system that measure and process data from array of magnetic sensors. The system allows to acquire up to 24 channels of NDT signals and uses automatic algorithms to process them in order to get information about begin of the belt loop, location of joints of particular belt segments and the final location and size of damages related to corrosion or cuts of steel cords inside belts. These techniques will be presented in the paper. Our approach has been validated in a lignite mine for several conveyor belts.

Abstract: Current maintenance of concrete civil infrastructure such as buildings, bridges, dams and highways, is based on scheduled inspection consisting in visual and/or local inspection techniques (i.e. acoustic/ultrasonic methods, radiography, eddy-current methods). A major trend in the field is the development of automated on-line monitoring systems. The current study is focused on the use of ultrasonic wave propagation techniques based on embedded piezoelectric transducers for the on-line monitoring of the damage state in concrete. The technique is based on the use of an ultrasonic emitter-receiver pair and the construction of a damage indicator focused on the early wave arrival. The proposed simple monitoring system is implemented during several pull-out tests on concrete blocks. The results demonstrate the excellent performance of the system which is able to detect the initiation and follow the evolution of the cracking until complete failure.

Abstract: The paper deals with the local damage detection in rolling element bearings in presence of a high level non-Gaussian noise. In many theoretical signal processing papers and engineering application related to damage detection, a simple model of the vibration is assumed. Basically it consists of signal of interest (SOI) and some unwanted (deterministic and/or random) components masking SOI in acquired observation. So, damage detection problem has to concern filtering, decomposition or extraction issue. Unfortunately, in the most of the industrial systems mentioned unwanted sources are in fact not Gaussian, so many of de-noising techniques cannot be applied directly or at least might give unexpected results. In this paper an industrial example will be discussed and novel approach based on advanced cyclostationary-based technique will be proposed. In the paper disturbances include periodic impacts in reciprocating compressor on an oil rig. Existing classical detection techniques (statistics in time domain, analysis of envelope spectrum, time-frequency decompositions) are insufficient to perform the task due to high power of disturbance contribution in comparison to damage signature. In the proposed technique, the Spectral Coherence Density Map (SCDM) is estimated first. Next step is related to analysis of SCDM contents and selection of informative part. If informative and non-informative components lay in separate frequency regions, such selection should fix the problem immediately

Abstract: This paper investigates the effect of low-frequency vibration and the related temperature field on nonlinear vibro-acoustic wave modulations. Experimental modal analysis was used to find natural frequencies and mode shapes of a composite laminate plate with seeded delamination. Temperature distribution was analyzed with a thermographic camera in the vicinity of damage for the identified vibration modes. These frequencies of these vibration modes were then used for low-frequency excitation in nonlinear acoustic tests. The correlation between the thermal field and the observed wave modulations was analyzed.