doi:10.3850/978-981-08-7619-7_P037

ABSTRACT

Despite of increasing popularity of 7-wire strand tendon for a cable-stayed bridge and geo-reinforcement system such as rock or soil anchor, no accurate or simple method is available for directly measuring the prestress force of those systems. The measurement of introduced prestress force is important for monitoring excessive wind or traffic loading, failure foreboding of retaining wall or soil slope, gauging the redistribution forces present after seismic event, and detecting corrosion via loss of the cross section on both geo-reinforcement system and cable-stayed bridge system. FBG Sensor, which is smaller than conventional strain gauge and has better durability and does not have a noise from electromagnetic waves, was embedded into the center king cable of 7-wire strand tendon. Ground anchor was simply made by using developed tendon, which embeds FBG sensors to measure the change of strain and anchor force. A series of laboratory tests were performed to verify the feasibility of FBG sensor as a measuring sensor of strain along the tendon. FBG sensor is proven very sensitive to the strain change of the tendon and strains measured from FBGs are comparable to those measured from conventional strain gauges. Prototype anchors were made by using FBG sensor embedded tendons and installed into the ground. Tension forces of each loading-unloading step are monitored using FBG sensors, which are located along free length area and fixed length area of the anchor, and conventional load cell. It was found that the prestress force which is monitored from FBG sensor located at free length area is comparable to that measured from conventional strain gauge type load cell. Through those pullout tests, FBG sensor embedded tendon is proven as the effective alternative monitoring tool of load cell from the introducing stage of prestress force to the long-term period for health monitoring of the geotechnical structure.

Keywords: FBG sensor, Ground anchor, Prototype anchor, Tension force.

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