After a bridge was completed, a faulting at supporting point may occur because of the unexpected loads to bridge bearing. Serviceability of bridges could be impaired by the faulting which had caused structural damage. Therefore, it is needed for a smart bridge bearing which can observe the supporting points continuously. Some of bridge bearings have been developed for measuring vertical load and vertical displacement by installing sensors in the bearing. However in those systems, it is not easy to be replaced with new sensors when repairs are needed. In this study, the smart bridge bearing of which sensors can be replaced has been developed to overcome such a problem. In this study, strain signals were used for measuring both vertical displacements and loads. Smart bridge bearings based on FBG sensors consist of EQS(Eradi Quake System) which has been commercially used for seismic bridge bearings. Experiments were carried out to prove applicability of the smart bridge bearing based on FBG sensors that can measure vertical displacements and loads.
Namhae Bridge, completed in May 1973, connects Namhae Island with mainland Korea in the province of Kyongsangnamdo. It is a three-span suspension bridge with a main span length of 404 m, and side spans of 128 m each. A geometric survey and static loading test was carried out and the deck geometry obtained from the survey was compared with the intended geometry of the original design. On the other hand, a long-term monitoring system for Namhae Bridge was employed in December 1996. The objective is to monitor the structural responses of the bridge with a view to identifying the deterioration rate over a long- term period. The monitoring system consists of 110 channels of both static and dynamic sensors such as strain gages accelerometers, tiltmeters, jointmeters and anemometers. A vehicle loading test was carried out in order to obtain the initial values of Namhae Bridge. An ambient vibration test for the whole bridge was carried out in 1999. Mode shapes as well as natural frequencies were found to give a more precise description of the current stage. These results will be used as a reference for the future monitoring.
Crack detection technique for concrete structures is developed in this paper. This method utilized Optical Time Domain Reflectormetry (OTDR) method that broadly used in the field of optical science. Currently several crack detection techniques, such as visual inspection, crack gage, ultrasonic detection test, are used. But these methods are not economical and are time-consuming issue. Therefore, easy and economical method of detecting cracks on the surface of concrete structure or welded part of steel structure have been developed in this research, this technique utilizes optical fiber and OTDR equipment. Concrete beam model tests are performed to verify the usefulness of this technique. Results of these tests show that developed technique can detect the location of the cracks easily and correctly. Further task is to testify the method of detecting cracks on welded part of steel structure with a performance of model test and apply it to a real structure.
In this study, the method to estimate the bridge deflection is developed using the fiber optic Bragg-grating strain sensors. Most of the evaluation of structural integrity, it is very important to measure the geometric profile, which is the major factor standing for the global behavior of civil structures, especially bridges. In the past, for the lack of the appropriate method to measure the deflection curve of bridge on site, the measurement was restricted to just a few of discrete points along the span length, which were also limited to the locations installed with the displacement transducer in advance. Hereby, with an application of classical beam theory, a formula is established estimating the continuously deflected profile from the measurement of strains at several points. In addition, strains could be measured by the use of fiber optic strain sensors, which are electro-magnetic noisy-free, and into which several points of sensing could be installed. With the strain data acquired, the proper strain curve is fitted, and finally, deflection curve would be estimated. The experimental test was carried out to verify the developed algorithm.