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Monitoring systems for masonry tunnels
Published in Hiroshi Yokota, Dan M. Frangopol, Bridge Maintenance, Safety, Management, Life-Cycle Sustainability and Innovations, 2021
Alfred Strauss, Hans Neuner, Corinna Harmening, Christian Seywald, Michael Österreicher, Elisabetta Pistone
Four sensor types were investigated with regard to the detection of strains. (1) Electrical resistance gauges have proven to be a good choice, as they score particularly for their comparatively simple assembly, low price and high accuracy. In case higher measuring frequencies are required, (2) fibre-optic sensors, which allow a high-accurate and high-frequent strain detection, are a well suited alternative. However, they require the largest financial expense of the four sensors under investigation. (3) Vibrating wire sensors are characterized by a comparatively large measuring range. However, as they are very sensitive with regard to vibrations, and can be disturbed by passing trains as well as the construction works, they are only suitable to a limited extent. As a fourth option, (4) MEMS sensors were investigated. However, they were excluded because of their drift and their comparatively low accuracy.
The experimental investigation of defects
Published in A. M. Sowden, The Maintenance of Brick and Stone Masonry Structures, 2020
The acoustic or vibrating-wire strain gauge is essentially a thin wire tensioned between end blocks which is plucked electromagnetically so that it vibrates. The electromagnetic circuit then counts the number of cycles of vibration in a given time and thus obtains the frequency of vibration. This frequency is related to the tension in the wire, and so if the end blocks are rigidly attached to a body undergoing strain, the tension in the wire and therefore the frequency of vibration will change. For a given gauge length, the strain change can be found from the frequency change. Provided that the anchorages at the ends of the wire do not move and the wire does not corrode, long-term stability is assured. An example of this device is shown in Fig. 6.4 and further discussion can be found in Tyler (1974).
Geotechnical instrumentation for in-situ measurements in deep clays
Published in B. Côme, P. Johnston, A. Müller, Design and Instrumentation of In Situ Experiments in Underground Laboratories for Radioactive Waste Disposal, 2022
D. Bruzzi, F. Gera, S. Piccoli, E. Tassoni
Vibrating-wire sensors have various advantages such as low cost, good repeatability, low hysteresis and high resolution and are easily connectable even in the case of long distance data transmission. The disadvantages of these sensors are their sensitivity to temperature change and to shocks and vibrations, large non-linearity, and a low frequency response.
Structural effects of temperature gradient on a continuous prestressed concrete girder bridge: analysis and field measurements
Published in Structure and Infrastructure Engineering, 2020
Tanvir Hossain, Seth Segura, Ayman M. Okeil
In this study, the temperature variation at a particular bridge segment of the recently completed John James Audubon Bridge Project in Louisiana is investigated analytically and through a field study. The case study segment is part of Bridge #2, which is a precast prestressed concrete girder bridge built using standard AASHTO Bulb-T girders (BT-72). A monitoring system has been installed on this bridge to study the effectiveness of a newly proposed continuity detail. All of the installed sensors are based on the vibrating wire technology and are capable of measuring the physical strain as well as the temperature at each monitored point (Okeil, Cai, Chebole, & Hossain, 2011). Each sensor was probed for a reading every 2.5 minutes and the hourly average temperature readings from these sensors were recorded and used for validation of the analytical method.
Lattice Boltzmann simulation for grout filling process during simultaneous backfill grouting of shield in tunnel construction
Published in European Journal of Environmental and Civil Engineering, 2020
Chang-ming Hu, Jian-xia Guo, Zhi-yu Wang
The vibrating wire earth pressure gauges with 165 mm in diameter and 0 ∼ 1000 kPa in measurement range, are used to measure the pressure acting upon the tunnel segment. The pressure acting on the pressure sensing plate makes the sensing plate deform. The deformation can be transferred to the vibrating wire and changes the vibrational frequency of the wire. The pressure can be obtained by measuring the vibrational frequency. The pressure gauges are mounted on the outer surface of the tunnel segment. The installation method of the earth pressure gauge is shown in Figure 3. The pressure gauge is fixed onto steel frame during the fabrication of the tunnel segment. A steel box surrounding the pressure gauge is mounted onto the segment to prevent detachment. A cover plate, which is made from Polyvinyl chloride (PVC) resin, is applied to overlay the face of sensing plate to prevent damage. The cable is penetrated to the inner face of the lining along the steel skeleton, and the end is fixed in pre-formed holes.