土木工程外文參考文獻

1、Engineering Structures 26 (2004) 1647–1657 www.elsevier.com/locate/engstructReview articleRecent applications of fiber optic sensors to health monitoring in civil engineeringHong-Nan Li a,?, Dong-Sheng Li a, Gang-Bing So

2、ng a,ba State Key Laboratory of Coastal and Offshore Engineering, Department of Civil and Hydraulic Engineering, Dalian University of Technology, Ganjingzi district, Linggong Road 2, Dalian 116024, China b Department of

3、Mechanical Engineering, University of Houston, Houston, TX 77204-4006, USAReceived 10 January 2003; received in revised form 11 May 2004; accepted 25 May 2004AbstractThis paper presents an overview of current research an

4、d development in the field of structural health monitoring with civil engineering applications. Specifically, this paper reviews fiber optical sensor health monitoring in various key civil structures, including buildings

5、, piles, bridges, pipelines, tunnels, and dams. Three commonly used fiber optic sensors (FOSs) are briefly described. Finally, existing problems and promising research efforts in packaging and implementing FOSs in civil

6、structural health monitoring are discussed. # 2004 Elsevier Ltd. All rights reserved.Keywords: Structural health monitoring; Fiber optic sensor; Civil health1. IntroductionStructural health monitoring has attracted much

7、attention in both research and development in recent years. This reflects continuous deterioration conditions of important civil infrastructures, especially long-span bridges. Among them, many were built in the 1950s wit

8、h a 40- to- 50-year designed life span. The collapses and failures of these deficient structures cause increas- ing concern about structural integrity, durability and reliability, i.e. the health of a structure throughou

9、t the world. Currently, there are no foot proof measures for structural safety. A structure is tested for deteriorations and damages only after signs that result from fault accumulations are severe and obvious enough. Wh

10、en the necessity of such tests becomes obvious, damages have already exacerbated the system’s reliability in many cases and some structures are even on the verge of collapse. Though routine visual inspection is manda-tor

11、y for important structures in some countries, for instance, bridges in the US, its effectiveness in finding all the possible defects is questionable. A recent survey by Moore et al. [1] of the US Federal Highway Admin- i

12、stration revealed that at most 68% of the condition ratings were correct and in-depth inspections could not find interior deficiencies considering the fact that visual examination by inspectors barely exists. Structural

13、health monitoring (SHM) refers to the use of in-situ, continuous or regular (routine) measurement and analyses of key structural and environmental para- meters under operating conditions, for the purpose of warning impen

14、ding abnormal states or accidents at an early stage to avoid casualties as well as giving mainte- nance and rehabilitation advice. This tentatively pro- posed definition of SHM complements that given by Housner [2]. This

15、 definition emphasizes the essence of the advance alert ability of SHM. In general, a typical SHM system includes three major components: a sensor system, a data processing system (including data acquisition, transmissio

16、n and storage), and a health evaluation system (including diagnostic algorithms and information management). The sensors utilized in SHM are required to monitor? Corresponding author. Tel.: +86-411-8470-8512x8208; fax: +

17、86- 411-8470-8501. E-mail address: hnli@dlut.edu.cn (H.-N. Li).0141-0296/$ - see front matter # 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.engstruct.2004.05.018chemical parameters. As a consequence, fiber opti

18、c based measurement systems have made the transition from research laboratories to practical engineering applications, and have found wide applications in aero- space, composites, medicine, chemical products, con- crete

19、structures, and in the electrical power industry. The market volume of FOSs is hypothesized to rise from US$ 305 millions in 1997 to this year’s US$ 550 millions [18], among which temperature, strain and pressure sensors

20、 account for about 40% of the total FOS products [19]. Extensive efforts are now engaged to realize economic FOSs and associated interrogation systems and to explore wider engineering applications. Optical fibers, which

21、usually consist of three layers: fiber core, cladding and jacket, are dielectric devices used to confine and guide light. The majority of optical fibers used in sensing applications have silica glass cores and claddings,

22、 and the refractive index of the cladding is lower than that of the core to satisfy the condition of Snell’s law for total internal reflection and thus confine the propagation of the light along the fiber core only. The

23、outer layer of a FOS, called jacket, is usually made of plastic to provide the fiber with appro- priate mechanical strength and protect it from damage or moisture absorption. In some sensing applications, a specialized j

24、acket is required to enhance the fiber’s measurement sensitivity and to accommodate the host structure. In general, an FOS is characterized by its high sensi- tivity when compared to other types of sensors. It is also pa

25、ssive in nature due to its dielectric construction. Specially prepared fibers can withstand high tempera- ture and other harsh environments. In telemetry and remote sensing applications, it is possible to use a seg- ment

26、 of the fiber as a sensor gauge and a long length of the same or another fiber to convey the sensed infor- mation to a remote station. Deployment of distributed and array sensors covering extensive structures andgeograph

27、ical locations is also feasible. With many sig- nal processing devices (splitter, combiner, multiplexer, filter, delay line, etc.) being made of fiber elements, an all-fiber measuring system can be realized.Table 1 lists

28、 the FOSs available to civil engineering applications and their categories. One method of classifying FOSs is based on its light characteristics (intensity, wavelength, phase, or polarization) that is affected by the par

29、ameter to be sensed. Another method classifies an FOS by whether the light in the sensing segment is modified inside or outside the fiber (intrinsic or extrinsic). FOSs can also be classified as local (or point), quasi-d

30、istributed and distributed sen- sors depending on the sensing range. This method of classification is adopted here to organize the rest of this section.2.1. Local fiber optic sensorsMany intensity based sensors, such as

31、microbend sensors, and most of the interferometric FOSs are local sensors, which can measure changes at specified local points in a structure. Interferometric FOSs are by far the most commonly used local sensors since th

32、ey offer the best sensitivity. This sensing technique is based primarily on detecting the optical phase change induced in the light as it propagates along the optical fiber. Light from a source is equally divided into tw

33、o fiber-guided paths (one is a reference path). The beams are then recombined to mix coherently and form a ‘‘fringe pattern’’ which is directly related to the optical phase difference experienced between the two optical

34、beams. The most common configurations of such inter- ferometric sensors are the Mach-Zehnder, Michelson and Fabry–Perot FOSs [20,21]. Among them, the Fabry–Perot (F-P cavity) FOS and the so-called long gage FOS (LGFOSs)

35、are the two types of local sensors commonly utilized in civil engineering. Fabry–PerotTable 1 Fiber optic sensors for civil structural health monitoringSensors Mesurands Linear response Resolution Range Modulation method

36、 Intrinsic/ extrinsicLocal Fabry–Perot Straina Y 0.01% gage lengthc 10,000 le Phase Both Long gage sensor Displacement Y 0.2% gage lengthd 50 m Phase IntrinsicQuasi- distributed Fibre Bragg grating Strainb Y 1 l strain 5

37、000 le Wavelength IntrinsicDistributed Raman/Rayleigh (OTDR) Temperature/strain N 0.5 m/1 vC 2000 me Intensity IntrinsicBrillouin (BOTDR) Temperature/strain N 0.5 m/1 vC 2000 m Intensity Intrinsica Can be configured to m

38、easure displacement, pressure, temperature. b Can be configured to measure displacement, acceleration, pressure, relative fissure and inclination, etc. c Resolution as high as 0.1 l strain. d Resolution as high as 0.2 l