1,720,976 research outputs found
Neural Network Novelty Filtering for Anomaly Detection
No full textA sophisticated long-term monitoring system is devised by the Hong Kong SAR government authorities to monitor the structural health and performance of the suspension Tsing Ma Bridge and the cable-stayed Kap Shui Mun Bridge and Ting Kau Bridge. The sensing system comprises about 900 permanently installed sensors including accelerometers, strain gauges, displacement transducers, anemometers, level sensors, temperature sensors and weigh-in-motion sensors. Based on this system, the Hong Kong Polytechnic University is devoted to developing a neural network based damage alarming system by use of the measurement data of modal properties, strain and fatigue properties, static displacement and deflection, and cable static force respectively. This paper describes how to establish a neural network novelty filter for anomaly detection of Tsing Ma Bridge cables from the measured multi-mode frequencies of the cables. An auto-associative neural network is developed for this purpose. Only a series of measured modal data in structural healthy state are required in training the neural network. Another series of measured modal data in testing phase are fed into the trained network to obtain a novelty index sequence that signals whether anomaly occurs. A salient feature of this approach is that it needs neither structural model nor damage model in both training and testing phases. Moreover, it is intrinsically tolerant of measurement noise and uncertainty in ambient conditions. Numerical simulation using noise-corrupted analytical data of the Tsing Ma Bridge cables is performed to demonstrate the effectiveness of the proposed novelty filter and its robustness to measurement and structural uncertainty
Evaluation of typhoon induced fatigue damage using health monitoring data for the Tsing Ma bridge
No full textThis paper aims to evaluate the effect of typhoons on fatigue damage accumulation in steel decks of long-span suspension bridges. The strain-time histories at critical locations of deck sections of long-span bridges during different typhoons passing the bridge area are investigated by using on-line strain data acquired from the structural health monitoring system installed on the bridge. The fatigue damage models based on Miner's Law and Continuum Damage Mechanics (CDM) are applied to calculate the increment of fatigue damage due to the action of a typhoon. Accumulated fatigue damage during the typhoon is also calculated and compared between Miner's Law and the CDM method. It is found that for the Tsing Ma Bridge case, the stress spectrum generated by a typhoon is significantly different than that generated by normal traffic and its histogram shapes can be described approximately as a Rayleigh distribution. The influence of typhoon loading on accumulative fatigue damage is more significant than that due to normal traffic loading. The increment of fatigue damage generated by hourly stress spectrum for the maximum typhoon loading may be much greater than those for normal traffic loading. It is, therefore, concluded that it is necessary to evaluate typhoon induced fatigue damage for the purpose of accurately evaluating accumulative fatigue damage for long-span bridges located within typhoon prone regions
Damage detection of long-span cable-supported bridges
No full textIn Hong Kong, a sophisticated long-term monitoring system called Wind and Structural Health Monitoring System (WASHMS) has been devised by the Highways Department of the Hong Kong SAR Government to monitor the structural health and performance of three long-span cable-supported bridges after their construction. This on0-structure instrumentation system consists of about 800 permanently installed sensors, including vibration transducers which makes it possible to monitor deterioration and detect potential structural damage from vibration measurement.\ud
The basic premise of vibration-based damage identification is that damage will alter the mechanical properties of a structure, which, in turn, alters the dynamic response of the structure. In the present study, in order to understand the effect of structural damage on the dynamic properties in the three brides, precise three-dimensional finite element models for the bridges have been formulated for simulation study. Various damage scenarios and the corresponding modal sensitive analyses are pursued. A neural network based multi-stage diagnosis strategy is then applied to identify damage occurrence, location and type for the three bridges, in accordance with the WASHMS. Finally, the potential application of some innovative techniques for damage detection of large-scale structures and future perspective in this field are briefly addressed
Fatigue Evaluation and Detection of Critical Fatigue Location for Bridge Deck Sections
No full textThis paper presents an effective approach for fatigue evaluation and detection of deck sections for bridges with online structural health monitoring system, The strain-time history recorded by the structural health monitoring system under actual traffic loading is investigated, and the strategy for fatigue evaluation of bridge decks on basis of the structural health monitoring data is provided for blocked repealed cycles of strain history, The effective stress range is used to evaluate the fatigue strength at different location of the bridge deck and to detect the critical location for possible fatigue failure, Calculated results of the fatigue evaluation and detection of critical locations arc given for a deck section of the Tsing Ma Bridge
Evaluation of typhoon induced fatigue damage for Tsing Ma Bridge
No full textThis paper aims to evaluate the effect of a typhoon on fatigue damage in steel decks of long-span bridges. The strain-time histories at critical locations of deck sections of long-span bridges during a typhoon passing the bridge area are investigated by using on-line strain data acquired from the structural health monitoring system permanently installed on the bridge. The fatigue damage models based on Miner's law and the continuum damage mechanics are applied to calculate increment of fatigue damage due to the action of a typhoon. The analytical results for the Tsing Ma Bridge show that the stress spectrum generated by a typhoon is much different than that by the normal traffic and its histogram shapes can be described approximately as a Rayleigh distribution. The influence of typhoon loading on accumulative fatigue damage is more significant than that due to normal traffic loading. The increment of fatigue damage generated by hourly stress spectrum for the maximum typhoon loading may be much greater than that by daily stress spectrum for normal traffic loading. The results suggest that it is necessary to evaluate typhoon induced fatigue damage for the purpose of accurately evaluating accumulative fatigue damage for the long-span bridge located at the typhoon prone region
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Studies of Overload Effect on Fatigue Damage of Steel Bridges
No full textPossible accidental overloading on a bridge occurs when an unexpected disaster happens. This paper studies the overloading effect on the fatigue damage of bridges on the basis of a nonlinear fatigue damage model. The model is applied to evaluate the fatigue damage and service life of the Tsing Ma Bridge (TMB), under normal traffic loading and possible accidental overloading. The calculated results under simulated con¬ditions for TMB showed the significant effect of overloading on the fatigue accumulation and residual life of the bridge. Typhoons are a significant factor in the design of bridges in Hong Kong. With the help of the data acquired by the Wind and Structural Health Monitoring System (WASHMS) installed in TMB, it is possible to investigate whether a typhoon will generate an overstress range in the local members ofTMB. It is concluded that typhoons do not usually generate local overstress inside bridges like TMB
Health Monitoring and Fatigue Damage Assessment of the Bridge Deck Sections
No full textBased on the real-time monitoring data, a fatigue damage model using continuous damage mechanics and a methodology and strategy for evaluating fatigue damage and possible critical locations of local fatigue on bridge-deck sections are developed. The proposed local damage model to evaluate the fatigue damage of bridge-deck sections allows\ud
fatigue damage to be considered at a continuum scale as a deteriorating process with its physical mechanism such as fatigue crack initiation and growth. Therefore the fatigue damage variable associates not only cycles of stress range on the accumulating process of fatigue, but also directly associates the state of deterioration and the mechanics behavior. The effective stress range for the variable-amplitude stress spectrum due to traffic load is used to evaluate the fatigue strength of the bridge-deck section at different locations, by which possible location of critical fatigue failure can be primarily determined. As a typical case to use the method and strategy proposed in this paper, fatigue damage assessment and the detection of possible critical location of fatigue in a deck section of the Tsing Ma Bridge are carried out by using strain-time history acquired by the bridge structural health monitoring system
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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