SEISMIC TESTING OF A ONE-FIFTH SCALE STRUCTURE WITH A FIBRE-OPTIC GYROSCOPE FOR ROTATION MEASUREMENT

The effect of the structural rotations has been traditionally neglected in the studies on the seismic response of structures. Because their influence was thought to be small and there were no suitable sensors available to measure the structural rotations properly. Different types of inertial rotation sensors have now reached the necessary sensitivity to be used to investigate the rotations of civil engineering structures. This paper presents experimental research on the feasibility of the use of a novel fibre-optic gyroscope (FOG) for measuring rotations in structural engineering. The FOG is a passive optical interferometer that uses the Sagnac effect to detect mechanical rotations such as tilts or torsions. The rotation rates measured by the FOG are absolute with respect to the local universe. Therefore, the measurement device does not require an external reference frame for operation. The FOG is light, compact and easy to install. To investigate the suitability of the FOG to measure rotations, a series of shake table tests were performed on a four-storey one-fifth scale structure equipped with the interferometer. Four different earthquake ground motions were used as input to the shake table. During the seismic testing, the FOG was attached to one of the first floor columns of the test structure to measure the rotation rates of the column. Relative displacements at the first floor were calculated from the rotation measurements provided by the FOG. The measurements were compared with those obtained by a conventional linear potentiometer. An excellent agreement was observed between both measurement techniques. The experimental results validated the accuracy of the measurements recorded by the FOG and the suitability of the sensor for applications in structural engineering.