• Structural Monitoring and Maintenance
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• v.1 no.3
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• pp.309-322
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• 2014

Detection of fatigue cracks at an early stage of their development is important in structural health monitoring. The breathing of cracks in a structure generates higher harmonic components of the exciting frequency in the frequency spectrum. Previously, the residual operational deflection shape (R-ODS) method was successfully applied to beams with a single crack. The method is based on the ODSs at the exciting frequency and its higher harmonic components which consider both amplitude and phase information of responses to map the deflection pattern of structures. Although the R-ODS method shows the location of a single crack clearly, its identification for the location of multiple cracks in a structure is not always obvious. Therefore, an improvement to the R-ODS method is presented here to make the identification process distinct for the beams with multiple cracks. Numerical and experimental examples are utilised to investigate the effectiveness of the improved method.

• Smart Structures and Systems
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• v.11 no.4
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• pp.365-386
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• 2013

Monitoring systems currently applied to concrete bridges include strain gauges, inclinometers, accelerometers and displacement transducers. In general, vertical displacements are one of the parameters that more often need to be assessed because their information reflects the overall response of the bridge span. However, the implementation of systems to continuously and directly observe vertical displacements is known to be difficult. On the other hand, strain gauges and inclinometers are easier to install, but their measurements provide no more than indirect information regarding the bridge deflection. In this context, taking advantage of the information collected through strain gauges and inclinometers, and the processing capabilities of current computers, a procedure to evaluate bridge girder deflections based on polynomial functions is presented. The procedure has been implemented in an existing software system - MENSUSMONITOR -, improving the flexibility in the data handling and enabling faster data processing by means of real time visualization capabilities. Benefiting from these features, a comprehensive analysis aiming at assessing the suitability of polynomial functions as an approximate solution for deflection curves, is presented. The effect of boundary conditions and the influence of the order of the polynomial functions on the accuracy of results are discussed. Some recommendations for further instrumentation plans are provided based on the results of the present analysis. This work is supported throughout by monitoring data collected from a laboratory beam model and two full-scale bridges.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2008.04a
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• pp.761-765
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• 2008

This study presents an effective methodology on integrated monitoring system for a maglev guideway using WDM-based FBG sensors. The measuring quantities include both local and global quantities of the guideway response, such as stains, curvatures, and vertical deflections. The strains are directly measured from multiplexed FBG sensors at various locations of the test bridge followed by curvature calculations based on the plane section assumption. Vertical deflections are then estimated using the Bernoulli beam theory and regression analysis. Frequency contents obtained from the proposed method are compared with those from a conventional accelerometer. Verification tests were conducted on the newly-developed Korean Maglev test track. It has been shown that good agreement between the measured deflection and the estimated deflection is achieved. The difference between the two peak displacements was only 3.5% in maximum and the correlations between data from two sensing systems are overall very good. This confirms that the proposed technique is capable of tracing the dynamic behavior of the maglev guideway with an acceptable accuracy. Furthermore, it is expected that the proposed scheme provides an effective tool for monitoring the behavior of the maglev guideway structures without electro magnetic interference.

• Journal of the Korean Society for Railway
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• v.9 no.4 s.35
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• pp.467-472
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• 2006

This paper deals with the applicability of long-gauge deformation fiber optic sensors (FOS) to prestressed concrete structures. A main motivation is the desire to monitor the deflection of the railway bridges without intervenes of the signal intensity fluctuations. A 25 m long, 1.8 m deep PSC girder was fabricated compositely with 22 cm thick reinforced concrete deck. Two pairs of 3 m long-gauge sensors are attached to the prestressed concrete girder with parallel topology. Using the relationship between curvature and vortical deflection and the quadratic regression of curvatures at the discrete point, it is possible to extrapolate the deflection curve of the girder. The estimated deflection based on the developed method is compared with the results using conventional strain gauges and LVDTS. It has been demonstrated that the proposed instrumentation technique is capable of estimating the vertical deflection and neutral axis position of the prestressed concrete girder up to weak nonlinear region.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2013.11a
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• pp.102-103
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• 2013

The use of inclinometer to measure deflections of structures is tested through experiments. By placing sensors at the ends of specimens, which are easy to accessed, the maximum deflection of a beam at the center is measured. Upon changing load, the inclined angles are measured and then converted to deflection using mathematical relationship between the deflection and rotational angle. Through this research, it is expected to promote the use of inclinometers for structural health monitoring of buildings and civil structures.

• Smart Structures and Systems
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• v.31 no.2
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• pp.183-197
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• 2023

For long-span bridges with a structural health monitoring (SHM) system, environmental temperature-driven responses are proved to be a main component in measurements. However, anomalous structural behavior may be hidden incomplicated recorded data. In order to receive reliable assessment of structural performance, it is important to study therelationship between temperature and monitoring data. This paper presents an application of the cointegration based methodology to detect anomalies that may be masked by temperature effects and then forecast the temperature-induced deflection (TID) of long-span suspension bridges. Firstly, temperature effects on girder deflection are analyzed with fieldmeasured data of a suspension bridge. Subsequently, the cointegration testing procedure is conducted. A threshold-based anomaly detection framework that eliminates the influence of environmental temperature is also proposed. The cointegrated residual series is extracted as the index to monitor anomaly events in bridges. Then, wavelet separation method is used to obtain TIDs from recorded data. Combining cointegration theory with autoregressive moving average (ARMA) model, TIDs for longspan bridges are modeled and forecasted. Finally, in-situ measurements of Xihoumen Bridge are adopted as an example to demonstrate the effectiveness of the cointegration based approach. In conclusion, the proposed method is practical for actual structures which ensures the efficient management and maintenance based on monitoring data.

• Journal of the Korea institute for structural maintenance and inspection
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• v.16 no.1
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• pp.99-109
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• 2012

This study aimed to develop a Structural Health Monitoring System for steel beams in the manner of suggesting and verifying a theoretical formula for displacement estimation using strain gauges, and estimating the loading points and magnitude. According to the results of this study, it was found that when a load of 160kN (56% of the yield load) was applied, the error rate of the deflection obtained with a strain gauge at the point of maximum deflection compared to the deflection measured with a displacement meter was within 2%, and that the estimates of the magnitude and points of load application also showed the error rate of not more than 1%. This suggests that the displacement and load of steel beams can be measured with strain gauges and further, it will enable more cost-effective sensor designing without displacement meter or load cell. The Structural Health Monitoring System program implemented in Lab VIEW gave graded warnings whenever the measured data exceeds the specified range (strength limit state, serviceability limit state, yield strain), and both the serviceability limit state and strength limit state could be simultaneously monitored with strain gauge alone.

• Smart Structures and Systems
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• v.25 no.2
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• pp.169-181
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• 2020

Sensor placement is a crucial aspect of bridge health monitoring (BHM) dedicated to accurately estimate and locate structural damages. In addressing this goal, a sensor placement framework based on the deflection influence line (DIL) analysis is here proposed, for the optimal design of damage detection-oriented BHM system. In order to improve damage detection accuracy, we explore the change of global stiffness matrix, damage coefficient matrix and DIL vector caused by structural damage, and thus develop a novel sensor placement framework based on the Fisher information matrix. Our approach seeks to determine the contribution of each sensing node to damage detection, and adopts a distance correction coefficient to eliminate the information redundancy among sensors. The proposed damage detection-oriented optimal sensor placement (OSP) method is verified by two examples: (1) a numerically simulated three-span continuous beam, and (2) the Pinghu bridge which has existing real damage conditions. These two examples verify the performance of the distance corrected damage sensitivity of influence line (DSIL) method in significantly higher contribution to damage detection and lower information redundancy, and demonstrate the proposed OSP framework can be potentially employed in BHM practices.

• Smart Structures and Systems
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• v.14 no.3
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• pp.419-444
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• 2014

Within this paper a new approach for early damage detection in rotor blades of wind energy converters is presented, which is shown to have a more sensitive reaction to damage than eigenfrequency-based methods. The new approach is based on the extension of Gasch's proportionality method, according to which maximum oscillation velocity and maximum stress are proportional by a factor, which describes the dynamic behavior of the structure. A change in the proportionality factor can be used as damage indicator. In addition, a novel deflection sensor was developed, which was specifically designed for use in wind turbine rotor blades. This deflection sensor was used during the experimental tests conducted for the measurement of the blade deflection. The method was applied on numerical models for different damage cases and damage extents. Additionally, the method and the sensing concept were applied on a real 50.8 m blade during a fatigue test in the edgewise direction. During the test, a damage of 1.5 m length was induced on the upper trailing edge bondline. Both the initial damage and the increase of its length were successfully detected by the decrease of the proportionality factor. This decrease coincided significantly with the decrease of the factor calculated from the numerical analyses.

• 한국방재학회:학술대회논문집
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• 2008.02a
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• pp.473-476
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• 2008

Currently the number of bridge, large or small, throughout the nation reaches at least 20,000 which tend to increase year by year. Now some of the special bridges are professionally managed through the maintenance monitoring system and the number of bridges under the maintenance monitoring system will be increase. The deflection-measure of spans among the measuring items is important item for checking bridge-condition. This study made an investigation into the management reference and estimated the safety-factor of the management reference