ISSN:1122-8385    

DOI:10.1002/stc.4300070101

出版商:John Wiley&Sons, Ltd    

年代:2000

数据来源: WILEY

摘要:

AbstractIn this paper we present a fiber optic sensor that is designed for embedded applications and long term health monitoring of structures. The sensor design uses an induced phase discontinuity in the fiber Bragg grating to create a narrow pass‐band within the reflection spectrum of the grating. The position of this narrow window within the Bragg spectrum is used to monitor the sensor's health. Theoretical analysis and experimental results are presented for this class of self‐monitoring sensors. Related signal demodulation scheme is also discus

ISSN:1122-8385    

DOI:10.1002/stc.4300070102

出版商:John Wiley&Sons, Ltd    

年代:2000

数据来源: WILEY

摘要:

AbstractWe describe an experimental set‐up designed for detection of impending structural failure in large‐scale structures such as bridges or dams. Strain applied on any 2 metres section along a 25km standard telecommunication fibre can be detected. We demonstrate sufficient signal to noise ratio with a very limited number of acquisitions, which could be performed in less than 3 seconds with custom‐build electronics. All electrical instrumentation is located on one end of the sensing fibre, permitting an easy install

ISSN:1122-8385    

DOI:10.1002/stc.4300070103

出版商:John Wiley&Sons, Ltd    

年代:2000

数据来源: WILEY

摘要:

AbstractAn optical fibre sensor for bridge monitoring is presented. It pursues the sensing of heavy traffic loads, and in particular vibration monitoring.A simpleintensitydevice is conceived; it is calibrated under laboratory static loading.The paper reports and discusses the results of dynamic tests aimed at measuring the oscillations of a steel bar whose bottom end is fixed to a shaking‐table. The table is driven by a hydraulic actuator capable of providing an assigned horizontal movement of different amplitude and frequency conten

ISSN:1122-8385    

DOI:10.1002/stc.4300070104

出版商:John Wiley&Sons, Ltd    

年代:2000

数据来源: WILEY

摘要:

AbstractFiber‐optic strain sensors to be used in materials research and for long‐term monitoring the state of chemically stressed concrete, e. g. sewer pipes, cooling towers, have to be intimately embedded in cement matrices. They should be coated with very thin alkaline‐resistant coatings. This is necessary to achieve a reliable strain transfer from the matrix to the fiber sensor.In order to clarify possible ways to replace thick coatings, which are unstable in cement environment, optical fibers have been modified and investigated with regard to their chemical compatibility, their strength behavior after alkaline attacks and their adhesion behavior to the matrix. The surface state of differently treated optical fibers intended for embedding has been characterized; additional strength estimation of alkaline attacked fibers was carried out. All estimations have been compared with those of bare alkaline attacked fibers.The real adhesion behavior was determined using the fiber push‐in test technique (indentation). Recent results suggest that fibers coated with very thin organic layers have remarkable adhesion properties. However, the fiber strength after exposing to alkaline pore solution (pH = 13.9) is worse than that of bare fibers. Optimum fiber/cement bond strength showed fibers, which were coated with a crosslinked polymer, produced in gas

ISSN:1122-8385    

DOI:10.1002/stc.4300070105

出版商:John Wiley&Sons, Ltd    

年代:2000

数据来源: WILEY

摘要:

AbstractFiber optic sensors capable of measuring chloride ion concentrations within concrete structures have been developed. The sensors rely on a modification of Fajan's method for chemical reagent identification resulting in spectral changes occurring when a predetermined concentration level has been exceeded. While not a reversible process, the sensor housing has been designed such that components with different chloride concentration thresholds may be exchanged in a field setting once the unit has been embedded into the concrete structure. These sensors have been embedded into three bridges in Vermont. Details of the sensors, the installation process, and measurements from these instrumented structures are presented.

ISSN:1122-8385    

DOI:10.1002/stc.4300070106

出版商:John Wiley&Sons, Ltd    

年代:2000

数据来源: WILEY

摘要:

AbstractCondition Monitoring of civil structures is best accomplished by way of distributed sensors. Sensors capable of making distributed measurements allow for monitoring the entire structure. Optical fiber sensors are especially very attractive for this purpose, since they are geometrically versatile and they can be readily integrated within various types of structures and materials. The research presented here describes the development of a new optical fiber sensor system for measurement of structural strains based on white light interferometry. Individual sensors are linked in series and an optical switch provides for multiplexing of strain signals from various locations in the structure. Bragg grating type fiber optic sensors as well as strain gauges were employed for comparison and verification of strain signals as measured by the new system. The system provides capability for distributed sensing of strains in large structures.

ISSN:1122-8385    

DOI:10.1002/stc.4300070107

出版商:John Wiley&Sons, Ltd    

年代:2000

数据来源: WILEY

摘要:

AbstractPreliminary experiments leading to the development of an optical fiber acoustic emission sensor is described. The objective was to develop a single sensor for simultaneous detection of acoustic emission events, from many locations within a large structure. The optical fiber sensor can be adhered to the surface of structural materials, i.e. steel or concrete. There are no individual sensor arrays or components built into the fiber. This characteristic provides simplicity and renders the system practical for applications in bridge structures. Alternatively, the optical fiber could be embedded in new concrete construction. Acoustic emissions from micro‐cracks or defects from various locations in the structure create stress wave perturbations in the optical fiber that are detected by a portable interferometer. Time‐domain measurements are instantaneous, in real‐time, and the entire structure is interrogated through a one‐time operation. The time domain signal acquired from the optical fiber discerns the number and locations of damage zones i.e., weld cracks, bolt‐hole cracks, corrosion activity, or brittle fracture of fibers in composite

ISSN:1122-8385    

DOI:10.1002/stc.4300070108

出版商:John Wiley&Sons, Ltd    

年代:2000

数据来源: WILEY

ISSN:1122-8385    

DOI:10.1002/stc.4300070109

出版商:John Wiley&Sons, Ltd    

年代:2000

数据来源: WILEY

ISSN:1122-8385    

DOI:10.1002/stc.4300070110

出版商:John Wiley&Sons, Ltd    

年代:2000

数据来源: WILEY