Plastic optical fibres have been employed to detect initial cracks, monitor post-crack vertical deflection and detect failure cracks in concrete beams subjected to flexural loading conditions. The intensity-based sensor system relies on monitoring the modulation of light intensity within the optical fibre as the sensor is loaded. The sensor design offers good signal stability and sensitivity to the monitored parameter and represents a cost-effective alternative to other more sophisticated health-monitoring systems currently used in civil engineering structures.Here, a series of three-and four-point bend tests was conducted on a range of structures. Initially, the optical fibres were attached to scale-model concrete samples (without reinforcement) to evaluate their ability to monitor beam deflection and detect cracks. Similar tests were subsequently conducted on life-size concrete beams containing reinforcing steel bars. The location and subsequent trajectory of cracks during the loading regime were marked and then compared to the sensor signal to assess the sensor's ability to monitor crack development.The results demonstrate the possibility of using optical fibres to detect hairline cracks and ultimate failure crack in civil engineering structures and highlight their ability to monitor crack propagation up to ultimate failure. In addition to detecting the initiation of a crack, good agreement between the sensor output and crack progression during loading was also obtained in these concrete beams.

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The purpose of this study was to find out how the principal's strategy in leading teachers and employees in the utilization of various educational resources and the effortprincipals In overcoming obstacles to improve the quality of graduates at SMA N 12 Banda Aceh.This research used qualitative approach with descriptive method. The subjects in this study were principals, teachers, employees and the administration. School supervisors and school committees.The technique of collecting the data wereinterview,observation and documentation.The results of this study showed (1) the principal's strategy in improving the quality ofgraduates in SMA N 12 Banda Acehincluding performing the principal's task as EMASLIM, involving teachers in RPS, MGMP development, conduct teacher professional development and curriculum through workshop activities,study seminars and others. (2) In an effort to improve the quality of graduates at SMA N 12 Banda Aceh, the principal had made the use of various resources that exist professionally, strengthening teacher tasks / professionalism, and involving the community in order to successing the 12-year compulsory education program and the improvement of faith and piety to God Almighty. (3) The principal's strategy in overcoming barriers to quality improvement of graduates at SMA N 12 Banda Aceh, such as, by involving the community in school programs through school committees both quality improvement and fund handling, developing and improving teachers' understanding of the curriculum substance.

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