Abstract
Measurement of sub-millimetre-level deformations of structures in the presence of ambient temperature changes can be challenging. This paper describes the measurement of a structure moving due to temperature changes, using two ShapeAccelArray (SAA) instruments, and verified by a geodetic monitoring system. SAA is a geotechnical instrument often used for monitoring of displacements in soil. SAA uses micro-electromechanical system (MEMS) sensors to measure tilt in the gravity field. The geodetic monitoring system, which uses ALERT software, senses the displacements of targets relative to control points, using a robotic total station (RTS). The test setup consists of a central four-metre free-standing steel tube with other steel tubes welded to most of its length. The central tube is anchored in a concrete foundation. This composite “pole” is equipped with two SAAs as well as three geodetic prisms mounted on the top, in the middle, and in the foundation. The geodetic system uses multiple control targets mounted in concrete foundations of nearby buildings, and at the base of the pole. Long-term observations using two SAAs indicate that the pole is subject to deformations due to cyclical ambient temperature variations causing the pole to move by a few millimetres each day. In a multiple-day experiment, it was possible to track this movement using SAA as well as the RTS system. This paper presents data comparing the measurements of the two instruments and provides a good example of the detection of two-dimensional movements of seemingly rigid objects due to temperature changes.
Highlights
Automated geodetic and geotechnical monitoring systems are playing a rapidly-increasing role in risk-reduction efforts concerning structures and their interaction with soils
Geodetic monitoring systems originated in the measurements and representation of the surface of the Earth, while the geotechnical systems originated in the study of behaviour of earth materials ([5])
Geodetic monitoring systems are represented in this paper by an automated deformation monitoring system developed by the Canadian Centre for Geodetic Engineering at the University of New Brunswick
Summary
Automated geodetic and geotechnical monitoring systems are playing a rapidly-increasing role in risk-reduction efforts concerning structures and their interaction with soils. The test setup described in this paper is located in Hanwell, New Brunswick, Canada It consists of two 4-metre vertical SAAs (with eight 50 cm long segments) inserted in 2.5 cm diameter steel pipes. The data for this experiment were collected on September 18-20, 2013. The data collected by the two SAAs for about two months prior to the experiment indicate that there is about 2 mm movement observed on the top of the pole, in mostly the North-South direction This knowledge led to the selection of a RTS with a one arc second angular resolution. The precision of the 4 m long SAA is specified to be 0.53 mm ([4])
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