A 64-channel data acquisition system (M/s Dewetron) was used for acquiring the data continuously from all the sensors. The sensors used with this acquisition system consisted of a LVDT to measure displacements, namely, vertical crown displacements and horizontal springing displacements; electrical resistance strain gauges to measure surface strains in a particular direction, either along the circumferential direction of the arch or the arch barrel- at the crown, quarter, and three-quarter point and springing levels and on the rails; vibrating wire strain gauges mounted on the arch and parapet; and uniaxial and triaxial accelerometers to measure the acceleration levels in terms of g levels at the track level (sleepers) and corresponding locations on the arch surface. A temperature sensor was fixed on the bridge to measure variations in the temperature. A tilt sensor was placed on the vertical surface of the pier. The LVDTs were located to measure the movement in arch surface, and strain gauges were located on the arch intrados, parapet, and rail. To check whether any activity in the form of movement or cracking takes place on the outside or inside of the arch, eight acoustic sensors were installed underneath on the right half portion (Castle Rock-CR) of Span 1.
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