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Subject: search.filters.subject.Bridge scour

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    Item type:Item,
    Applicability and limitations of time domain reflectometry bridge scour monitoring system in general field conditions
    (1970-01-01)
    Wang, Kai
    ;
    Lin, Chih-Ping
    ;
    土木工程學系
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    Department of Civil Engineering
    A real-time and durable system for scour process monitoring with sufficient spatial precision is in pressing need for bridge safety management. In light of this, an innovative bundled time domain reflectometry sensing cable was recently proposed to enhance the time domain reflectometry technique for scour monitoring. However, current development only dealt with the construction of bundled sensing cable and the corresponding new data reduction method. Before it can be put into practical use, issues related to the effect of hydrological conditions, long-distance measurement, and actual field implementation are yet to be investigated. This study used both numerical simulations and laboratory experiments to examine the time domain reflectometry signals in response to both scour and deposition in different water-level conditions. As a result, the first guideline of waveform classification and interpretation is newly proposed to validly determine scour depth under various field conditions. Since field measurements often come with significant signal attenuation from resistance loss of long cable and dielectric and conductive loss in the sensing section, numerical simulations and a series of full-scale experiments were also conducted to assess the time domain reflectometry scour measurement range. The maximum measurement range of the latest time domain reflectometry scour sensing cable was found to be about 6 m. Within this range, the maximum error of scour estimation is within 0.2 m. Considering the new findings, a field time domain reflectometry scour monitoring system using the bundled time domain reflectometry sensing cable was designed accordingly and implemented at a bridge for the first time. The monitoring system successfully captured the scour process during a storm event and revealed some practical issues for future improvement as well.
  • Thumbnail Image
    Item type:Item,
    Development of a real-time scour monitoring system for bridge safety evaluation
    (2017-01-01)
    Lin, Tzu-Kang
    ;
    Chang, Yu-Shian
    ;
    土木工程學系
    ;
    Department of Civil Engineering
    The fact that hydraulic problems are major factors in bridge collapse has made bridge scour monitoring an important research topic. In view of the complex nonlinear behavior of bridge structure/soil/water interactions, the fundamental frequency of the bridge may gradually change as the height of the bed drops during scour. With an insufficient embedded depth, the bridge may collapse or sink unexpectedly without warning. As experimental investigation in past research has shown that bridge failure may be governed by rigid body motion, a real-time bridge scour monitoring system to distinguish the influence of rigid body motion from the vibration frequency of the bridge is proposed. The signal measured from the superstructure of the bridge is decomposed into a structural vibration set controlling the fundamental frequency change and a rigid body motion set controlling the rigid body motion, and an instability index to examine the safety condition of the bridge is further proposed. Following a successful preliminary single-pile scour experiment, the method is applied to a series of full-bridge testing. According to analysis result, the instability index deviated considerably from its original range before the bridge piles began tilting significantly, allowing an early warning alert for bridge safety evaluation. (C) 2016 Elsevier Ltd. All rights reserved.