This study presents a bridge monitoring system implementation for a test-bed structure, the Geumdang bridge which is a 122 (m) long, PSC box-girder highway bridge in operation in Korea. 3.5 Generation mobile telecommunication technology, HSDPA was used to make the bridge monitoring system in a remote site ready to access internet with little efforts. HSDPA Modem also enabled bridge monitoring system to carry out simple operations through short message service of mobile phone. Remote desktop software was used to make the monitoring system remotely controllable and maintainable through Internet. In the Geumdang bridge monitoring system, smart sensors such as optical fiber strain sensors and piezoelectric sensors were installed as well as convention accelerometers. Total four types of sensors including 3 temperature sensors, 25 accelerometers, 11 optical fiber strain sensors and 3 piezoelectric sensors were implemented to monitor system level behavior and element level behavior. Strain and acceleration measurement was used to monitor global behavior of the bridge subjected to environmental temperature change. Piezoelectric sensors were used to monitor an important structural element, which is a bridge bearing. The influence of environmental temperature change was eliminated from the measured electrical impedances acquired by the piezoelectric sensors. Dynamically measured acceleration and strain were used to carry out experimental modal analysis. Reference-based data-driven stochastic subspace identication algorithm was adopted due to its preciseness and powerful post-processing capability. Modal transfer norm was introduced to achieve automation of subspace algorithm.
본 연구는 3.5세대 이동통신을 이용한 교량 모니터링 시스템 구축에 관한 것이다. 3.5세대 이동통신인 HSDPA를 이용한 모니터링 시스템을 시험교량인 금당교에 설치하였다. 이동통신망을 활용함으로써 손쉽게 현장을 인터넷에 연결하도록 하였고, 관리자는 현장의 모니터링 시스템을 원격제어, 관리할 수 있도록 하였다. 휴대전화 문자메시지를 이용하여 현장의 인터넷 접속 제어를 수행하였고, 원격제어를 위해 범용의 원격 데스크탑 소프트웨어를 사용하였다. 금당교에는 25개의 가속도계와 11개의 광섬유 FBG 변형률계, 3개의 압전센서, 3개의 온도계가 설치되었다. 가속도계와 동적 변형률의 계측치는 교량의 전체적인 거동을 모니터링 하는데 사용되었고, 압전센서는 교량의 주요 부재인 교량 받침을 모니터링 하는데 사용되었다. 환경적인 온도 변화에 따른 교량의 거동의 변화를 관찰하였고, 임피던스 측정에 있어서 온도 변화에 영향을 보상하였다. 가속도 신호와 동적 변형률 계측 신호는 Data Driven Stochastic Subspace Identification을 사용하여 모드해석을 수행하였고, Modal Transfer Norm을 도입하여 Subspace Alogorithm의 자동화에 활용하였다.
