In this study, a structural health monitoring system for cable-stayed bridges is developed. In the system, condition assessment of the structure is performed based on measured records from seismic accelerometers. Response indices are defined to monitor structural safety and serviceability and derived from the measured acceleration data. The derivation process of the indices is structured to follow the transformation from the raw data to the outcome. The process includes noise filtering, baseline correction, numerical integration, and calculation of relative differences. The system is packed as a condition assessment program, which consists of four major processes of the structural health evaluation: (i) format conversion of the raw data, (ii) noise filtering, (iii) generation of response indices, and (iv) condition evaluation. An example set of limit states is presented to evaluate the structural condition of the test-bed and cable-stayed bridge.

Wireless sensors are more favorable in measuring structural response compared to conventional sensors in terms of them being easier to use with no issues with cables and them being considerably cheaper. Previous tests have been conducted to analyze the performance of MEMS (Micro Electro Mechanical Systems) sensor in sinusoidal excitation tests. This paper analyzes the performance of in-built MEMS sensors in devices by comparing with an ICP sensor as the reference. Earthquake input amplitude excitation in shaking table tests was done. Results show that MEMS sensors are more accurate in measuring higher input amplitude measurements which range from 100gal to 250gal than at lower input amplitudes which range from 10gal to 50gal. This confirms the results obtained in previous sinusoidal tests. It was also seen that natural frequency results have lower error values which range from 0% to 3.92% in comparison to the response spectra results. This also confirms that in-built MEMS sensors in mobile devices are good at estimating natural frequency of structures. In addition, it was also seen that earthquake input amplitudes with more frequency contents (Gyeongju) had considerably higher error values than Pohang excitation tests which has less frequency contents.

가속도로부터 변위를 계산 방법 중 상대적으로 사용이 간단한 변위재구성기법이 Lee et al.(2010)과 Hong et al.(2010)에 의해 제안되었다. 목표주파수는 변위재구성기법을 사용할 때 사용자가 결정해야 할 중요한 변수 중 하나로 이것을 결정하기 위해선 주파수영역 분석에 대한 경험이 필요하다. 이 논문은 지진하중을 받는 사장교에 한정된 변위재구성기법의 목표주파수 결정 방법을 제시한다. 사장교가 지진에 의해 가진될 경우 목표주파수는 유효한 모드의 고유주파수 중 가장 낮은 주파수로 결정된다. 여기서 유효한 모드라 함은 가속도의 자유도에 유의미한 영향을 주는 모드형상을 가진 모드를 의미한다. 제안된 목표주파수 결정방법의 타당성을 검증하기 위해 포항지진 발생 당시 측정된 3개 실 교량의 주경간 중앙에서 측정된 가속도와 변위 시간이력을 분석했다. 또한 제안된 방법을 포항지진 발생 당시 측정된 실교량의 주탑 상단 가속도에 적용해 계산된 변위를 분석했다.