ABSTRACT:Improving the efficiency of bridge inspection and minimizing the impact of dynamic load on the long term deterioration of the bridge structure reduces maintenance and upkeep costs whilst also improving bridge longevity and safety. This paper presents the results of an on-going project whose ultimate goal is the real-time photogrammetric monitoring the structural deformations of the second Bosphorus Bridge of Istanbul.
INTRODUCTIONBridges are exposed to intensive and dynamic loads, unsteady weather conditions, material fatigue and aging process. All these factors cause deformations on the construction parts. The importance of the monitoring and early identifying the bridge deformations is essential once the maintenance, repair and even the reconstruction costs are considered.Monitoring campaigns of long bridges are becoming more and more common as the research fields of structural health monitoring and performance monitoring grow.A very first photogrammetric bridge monitoring project, including a condition survey and vertical deflection measurement, was carried out by Bales and Hilton in 1985. The bridge has a 3-span continuous structure with a total length of 139 m. The length of the center span was measured as 51 m. The camera was positioned at three locations under mid-span facing up at a distance of about 10.8 m. The average difference between photogrammetric measurements and level readings was approximately 3 mm (Bales and Hilton, 1985).Kim (1989) performed a long-term deformation monitoring of a 526 m long highway bridge using photogrammetry. The project utilized a camera with a 150 mm lens. The distance between the bridge and the camera was 122 m. Images were recorded on conventional 230 x 230 mm film and were analyzed using a program developed specifically for the project. It was concluded that the precision of the deformation measurement using photogrammetry was within ±14 mm in the length and height directions, and ±30 mm in the width direction (Kim, 1989).Leitch (2002) and Jauregui et al. (2003) conducted a comprehensive study on bridge deflection measurement using close-range photogrammetry. Studies were performed on a laboratory steel beam and on two field bridges. The first bridge tested was a single-span, prestressed concrete bridge with a length of 32.2 m. The second was a simple-supported steel girder bridge, under truck loading and having 7-spans. In the experiments of the first bridge, photogrammetric measurements of the initial camber were compared with level rod readings.The maximum deviation of the two measurements was within ±17 mm for four of the girders, and 28 mm for the remaining girder (Leitch, 2002). For the second experiment; the photogrammetric measurement results were compared with those obtained from finite element analysis, level rod readings, and curvature-based measurements derived from strain gages.The maximum deflection was about 8 mm. The differences in deflection measurements from photogrammetry, curvature, and the level rod were within 0.5-1.5 mm for all girders a...