Browsing by Author "Chang, Kuo-Chun"

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A bridge safety monitoring system for prestressed composite box-girder bridges with corrugated steel webs based on in-situ loading experiments and a long-term monitoring database
(2016-11-01)
Sung, Yu-Chi
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Lin, Tzu-Kang
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Chiu, Yi-Tsung
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Chang, Kuo-Chun
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Chen, Kuo-Long
In order to reduce the self-weight of Highway No. 4 in the Taichung living circle in Taiwan, a corrugated steel web, with a span of 145 m, is used to replace the conventional concrete web. To appraise the structural safety and operating conditions of a prestressed composite box-girder bridge with a corrugated steel web, which is the first bridge of its kind in Taiwan, a bridge monitoring system is developed based on in-situ experiments, numerical modeling, and long-term monitoring. In order to determine the initial static and dynamic behaviors of a real bridge, a series of experiments are first carried out on a newly constructed bridge. Before entering service, a bridge is subjected to forced vibration experiments and static loading experiments to establish its initial condition. In this study, a numerical model of the bridge is constructed based on the finite element method. The results of the structural analysis are compared with experimental data, and the two sets of results are found to show good agreement. Moreover, thermometers, strain gages, displacement gages, and inclinometers are installed on the bridge to measure changes in the physical quantities, and the monitored temperature gradient profile over a year is fed back to the numerical model for further analysis. Results have indicated that the in-situ linear variable differential transformer (LVDT) and inclinometer monitoring data can be effectively simulated by the numerical model. Finally, based on the material properties, numerical model, and long-term monitoring data from inclinometers, the safety threshold of the bridge is determined to provide a useful reference for bridge management agencies. Prediction of the extreme inclination angles by the Generalized Extreme Value Distribution (GEVD) method for the 50-year life cycle of the monitored bridge also falls within the envelopes of the warning and critical thresholds, which support the long-term safety of bridges. (C) 2016 Elsevier Ltd. All rights reserved.
Analysis of Nonlinear Distortion and SSII Cancellation in EAM-Based IMDD OFDM Transmission
(2015-07-15)
Wei, Chia-Chien
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Cheng, Hsuan-Lin
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Chen, Hsing-Yu
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Chen, Yu-Chao
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Chu, Hsuan-Hao
In terms of second-order nonlinearity, nonlinear distortion in an EAM-based IMDD OFDM system is deterministically modeled as subcarrier-to-subcarrier intermixing interference ( SSII), such that DSP-based nonlinear compensation can be provided by decision-aided SSII cancellation at the receiver. The effectiveness of SSII cancellation heavily relies on the accuracy of SSII calculation, which is determined mainly by the modulation model adopted. This study made comprehensive comparisons of three small-signal models (constant-chirp, dynamic-chirp, and nonlinear-E/O models). We then combined theory and experiment results to examine the characteristics of SSII estimation and cancellation using various models, such as SSII spectra, regression coefficients, and correlation coefficients between the SSII and the total received errors, as well as the relationship between improvements in performance and the correlation coefficient. The nonlinear-E/O model is the most comprehensive, and as a result presents the flattest regression coefficient and highest correlation coefficient, which results in the most pronounced improvement in performance.
Analytical and experimental studies on building mass damper system with semi-active control device
(2018-06-01)
Liu, Yu-Fang
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Lin, Tzu-Kang
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Chang, Kuo-Chun
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土木工程學系
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Department of Civil Engineering
A concept of improving an optimum building mass damper (OBMD) system through a semi-active control method for enhancing the efficiency of controlling structural responses is proposed. The proposed concept entails replacing the passive fluid viscous dampers used in an OBMD system with semi-active magnetorheological dampers, thus transforming the system into a novel semi-active OBMD (SOBMD) system for better seismic performance. A numerical model based on the Bouc-Wen model with the interpolation technique was established to represent the behavior of the semi-active magnetorheological dampers. The SOBMD system was then developed on the basis of linear-quadratic regulator method and a continuous-optimal control concept. The damping force in the SOBMD system can be manipulated according to the structural response; therefore, the SOBMD system affords the possibility of improving the displacement or acceleration response compared with the original OBMD system. Both of the numerical analysis and the experimental verification demonstrated the superior seismic mitigation ability of the SOBMD system. Several earthquake events with different characteristics were simulated in a series of numerical analysis to further verify the performance of the proposed SOBMD system. In short, the benefits of both the active and passive control system are successfully combined in the proposed SOBMD system.
Compressive Column Load Identification in Steel Space Frames Using Second-Order Deflection-Based Methods
(2018-07-01)
Bonopera, Marco
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Chang, Kuo-Chun
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Chen, Chun-Chung
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Lin, Tzu-Kang
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Tullini, Nerio
This paper presents a comparison of two static nondestructive methods used to assess compressive loads in columns of steel space frames. The first method requires knowledge of the flexural rigidity of the column under investigation, whereas the second method requires knowledge of the column's buckling load. In each method, short-term displacements are measured at given cross-sections along the member under examination, which is subjected to an additional transverse load. The two methods were verified in this study through experimental and numerical tests on a column of a small-scale space frame prototype with generic connections and end conditions. Estimations of compressive forces were generally reliable when second-order effects were accurately considered. In conclusion, the two methods can be successfully used to test steel space frames in a laboratory or under real conditions.
Continuous structural health monitoring of the Sayano-Shushenskaya Dam using off-site seismic station data accounting for environmental effects
(2020-01-01)
Hsu, Ting-Yu
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Valentino, Arygianni
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Liseikin, Aleksei
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Krechetov, Dmitry
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Chen, Chun-Chung
Damage to a huge dam can cause great loss of human life and property, but disasters and their consequences can be minimized by implementing effective dam safety monitoring strategies. However, establishing a permanent monitoring system on a huge darn is costly. Additionally, for reasons of national security, many darns and information about them may not be able to be accessed by researchers. Accordingly, continuously monitoring the structural health of a dam by measurement may be difficult. This study presents a way to continuously monitor the health of a dam using vibration signals that are measured not on the dam but close to it. The Sayano-Shushenskaya Dam in Russia is used to demonstrate the idea. Intensive ambient vibration measurements were firstly made once to determine the natural frequencies of the dam. Then the natural frequencies of the dam under varying environmental effects are obtained from the spectra of the seismic records obtained at Cheryomushki seismic station, which is located 4.4 km northeast of the darn. To account for the effects of varying environmental conditions on the natural frequencies, an autoencoder in the form of an unsupervised learning neural network, was employed. The autoencoder was trained using the natural frequencies without using any environmental factors to learn the intrinsic behavior of the darn under varying environmental conditions. The errors between input data to the trained autoencoder and the regenerated data from the autoencoder can be used to determine whether the dam is under normal conditions. A finite element model of the dam was constructed to simulate changes of natural frequencies due to cracks in the dam structure. The results demonstrate that the proposed method can feasibly monitor the structural health of the dam.
Early Warning System Development for Highway Bridge Scouring
(2015-01-01)
Chang, Kuo-Chun
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Lin, Yung-Bin
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Chou, Wei-Ting
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交大名義發表
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National Chiao Tung University
Scour problem plays a key role in many bridge failures that occur around the globe. More than 1000 bridges have collapsed over the past 30 years in the U.S.A., with 60% of the failures due to scour. This serious problem also happens in many East-Asian countries such as Taiwan and Japan, owing to the fact that these areas are subject to several typhoon, hurricanes and flood events each year during the summer and fall seasons. Therefore, it is necessary to have a reliable estimation of scour hole around bridge piers to ensure that adequate measures are taken to prevent erosion related failure throughout the service life of the structure. Collaborated with the interdisciplinary institute of the National applied Research Laboratories (NARLabs), we have developed and successfully demonstrated the bridge multi-hazards early warning system in the field of Taiwan river basins.
Evaluation of bridge instability caused by dynamic scour based on fractal theory
(2013-07-01)
Lin, Tzu-Kang
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Wu, Rih-Teng
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Chang, Kuo-Chun
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Chang, Yu Shian
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土木工程學系
Given their special structural characteristics, bridges are prone to suffer from the effects of many hazards, such as earthquakes, wind, or floods. As most of the recent unexpected damage and destruction of bridges has been caused by hydraulic issues, monitoring the scour depth of bridges has become an important topic. Currently, approaches to scour monitoring mainly focus on either installing sensors on the substructure of a bridge or identifying the physical parameters of a bridge, which commonly face problems of system survival or reliability. To solve those bottlenecks, a novel structural health monitoring (SHM) concept was proposed by utilizing the two dominant parameters of fractal theory, including the fractal dimension and the topothesy, to evaluate the instability condition of a bridge structure rapidly. To demonstrate the performance of this method, a series of experiments has been carried out. The function of the two parameters was first determined using data collected from a single bridge column scour test. As the fractal dimension gradually decreased, following the trend of the scour depth, it was treated as an alternative to the fundamental frequency of a bridge structure in the existing methods. Meanwhile, the potential of a positive correlation between the topothesy and the amplitude of vibration data was also investigated. The excellent sensitivity of the fractal parameters related to the scour depth was then demonstrated in a full-bridge experiment. Moreover, with the combination of these two parameters, a safety index to detect the critical scour condition was proposed. The experimental results have demonstrated that the critical scour condition can be predicted by the proposed safety index. The monitoring system developed greatly advances the field of bridge scour health monitoring and offers an alternative choice to traditional scour monitoring technology.
Integration of in-situ load experiments and numerical modeling in a long-term bridge monitoring system on a newly-constructed widened section of freeway in Taiwan
(2014-06-01)
Chiu, Yi-Tsung
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Lin, Tzu-Kang
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Hung, Hsiao-Hui
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Sung, Yu-Chi
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Chang, Kuo-Chun
The widening project on Freeway No.1 in Taiwan has a total length of roughly 14 kilometers, and includes three special bridges, namely a 216 m long-span bridge crossing the original freeway, an F-bent double decked bridge in a co-constructed section, and a steel and prestressed concrete composite bridge. This study employed in-situ monitoring in conjunction with numerical modeling to establish a real-time monitoring system for the three bridges. In order to determine the initial static and dynamic behavior of the real bridges, forced vibration experiments, in-situ static load experiments, and dynamic load experiments were first carried out on the newly-constructed bridges before they went into use. Structural models of the bridges were then established using the fmite element method, and in-situ vehicle load weight, arrangement, and speed were taken into consideration when performing comparisons employing data obtained from experimental measurements. The results showed consistency between the analytical simulations and experimental data. After determining a bridge\'s initial state, the proposed in-situ monitoring system, which is employed in conjunction with the established fmite element model, can be utilized to assess the safety of a bridge\'s members, providing useful reference information to bridge management agencies.
Visible Light Communication System for Offshore Wind Turbine Foundation Scour Early Warning Monitoring
(2019-07-01)
Lin, Yung-Bin
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Lin, Tzu-Kang
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Chang, Cheng-Chun
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Huang, Chang-Wei
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Chen, Ben-Ting
Offshore wind farms have a superior wind source to terrestrial wind farms, but they also face more severe environmental conditions such as severe storms, typhoons, and sea waves. Scour leads to the excavation of sediments around the foundations of structures, reducing the safe capacity of the structures. The phenomenon of pier scour is extremely complex because of the combined effects of the vortex system involving time-dependent flow patterns and sediment transport mechanisms. A real-time scour monitoring system can improve the safety of structures and afford cost-effective operations by preventing premature or unnecessary maintenance. This paper proposes an on-site scour monitoring system using visible light communication (VLC) modules for offshore wind turbine installations. A flume experiment revealed that the system was highly sensitive and accurate in monitoring seabed scour processes. This arrayed-VLC sensory system, proposed in this paper, has considerable potential for safety monitoring and also can contribute to improving the accuracy of empirical scour formulas for sustainable maintenance in the life cycle of offshore structures.