Subject matter

Sensors and transducers are widely used in civil engineering for the measurement of parameters such as displacement, strain, acceleration, load and temperature. Traditionally, sensing instruments are mostly used in the laboratory to study structural behaviour or measure material properties. Recently, due to the growing interests in the condition assessment and monitoring of structures, field installation of sensors is becoming increasingly common. Conventional transducers and sensors are mostly based on electrical or magnetic principles. In comparison, optical fiber sensors possess a number of advantages, including
(i) low signal loss, therefore being suitable for remote sensing,
(ii) immunity to electromagnetic noises common in sensing applications
(iii) not vulnerable to damage by lightning, which is important to structures in open areas such as bridges or dams,
(iv) small size and lightweight; hence unobstructive when installed in a structure,
(v) possibility of multiplexing, i.e., having a number of sensing points along a single fiber,
(vi) feasibility of distributed sensing, as any point along the fiber can act as a sensor. With these advantages, optical fiber sensors have been employed (though in limited extent) to replace conventional sensors in structural monitoring applications. They have also been used in experimental research as tools to provide accurate and stable measurements in the laboratory. Actually, by exploiting the special properties of optical fibers, novel sensors can be designed to provide sensing capabilities not achievable with existing instruments, and hence make possible the acquisition of new information useful to the engineer. Examples include the distributed sensing of strain or cracking with time domain reflectometry, as well as the sensing of moisture change and steel corrosion. These novel applications have been demonstrated in the laboratory, and there is potential for field application in the near future.

While optical fiber sensors can exhibit improved performance and capabilities over electromagnetic counterparts, the costs of optical fiber sensing systems are also higher. They should therefore only be used if (i) conventional sensor fails to satisfy performance requirements (e.g., stability, accuracy, durability, etc) under specific conditions, or (ii) the optical sensor can provide useful information not obtainable with conventional sensors. To identify suitable applications of the optical fiber sensor, a good understanding of the principles and advantages of such sensors is required. Such understanding, however, is often lacking for civil engineers. We therefore propose a form a committee to review the current state-of-the-Art of fiber optic sensing and its application in civil engineering. Based on this information, reports and application guidelines will be developed to facilitate the use of this new technology in civil engineering practice.

Fiber optic sensing is a very broad field, and the proposed committee will only focus on principles and applications that are of direct relevance to civil engineering. Also, the design of light sources and signal processing units will be not covered. In the application guidelines to be developed, common optoelectronic components will be introduced as background information for civil engineers who have little experience with optical instrumentation.

Proposed terms of reference
The general objective of the committee is to promote the proper use of fiber optic sensors in civil engineering applications where their advantages can be fully exploited. To achieve the objective, the following tasks will be performed:

(1) The state-of-the-Art of fiber optic sensing will be reviewed, with particular focus on applications related to civil engineering. A State-of-the-Art report will then be published
(2) We will compile case studies related to the practical applications of optical fiber sensors, for in-situ monitoring of real structures, and as high precision and accurate measuring tools in laboratory studies. A document of case studies will be prepared
(3) A workshop on “Practical Applications of Optic Fiber Sensors in Civil Application” will be organized, to summarize existing status of sensor development, industrial needs of the technology, and how such needs can be fulfilled with available fiber optic sensing technologies.
(4) After the workshop, we will start to develop an application guideline for optical fiber sensors in civil engineering, with practical examples to demonstrate situations where optical fibers can have significant advantages over conventional sensors and transducers.
(5) A website focusing on “Fiber Optical Sensing in Civil Engineering” will be created for further communication of information after the completion of the committee’s work.

Members of the committee will be invited from universities, research institutes and companies from various parts of the world. It is important that the committee covers a wide range of expertise including (i) sensing principles, (ii) sensor design, fabrication and installation, (iii) sensor network design and instrumentation, (iv) behavior of structural system and components, (v) structural damage and material degradation mechanisms, and (vi) practical sensing needs and limitations of existing technologies. Knowledge in the first three areas is required for the development of useful sensors and their proper implementation in practice. Expertise in the last three areas is crucial for determining the type of information to be obtained, and how they should be interpreted to reflect the current condition of the structure or the material. With each member having strong technical background in one or more of the above areas, we expect to create a synergism within the committee that will facilitate the achievement of the various goals.

Terms of reference

The general objective of the committee is to promote the proper use of fiber optic sensors in civil engineering applications where their advantages can be fully exploited. To achieve the objective, the following tasks will be performed:

(1) The state-of-the-Art of fiber optic sensing will be reviewed, with particular focus on applications related to civil engineering. A State-of-the-Art report will then be published
(2) We will compile case studies related to the practical applications of optical fiber sensors, for in-situ monitoring of real structures, and as high precision and accurate measuring tools in laboratory studies. A document of case studies will be prepared
(3) A workshop on “Practical Applications of Optic Fiber Sensors in Civil Application” will be organized, to summarize existing status of sensor development, industrial needs of the technology, and how such needs can be fulfilled with available fiber optic sensing technologies.
(4) After the workshop, we will start to develop an application guideline for optical fiber sensors in civil engineering, with practical examples to demonstrate situations where optical fibers can have significant advantages over conventional sensors and transducers.
(5) A website focusing on “Fiber Optical Sensing in Civil Engineering” will be created for further communication of information after the completion of the committee’s work.

Members of the committee will be invited from universities, research institutes and companies from various parts of the world. It is important that the committee covers a wide range of expertise including (i) sensing principles, (ii) sensor design, fabrication and installation, (iii) sensor network design and instrumentation, (iv) behavior of structural system and components, (v) structural damage and material degradation mechanisms, and (vi) practical sensing needs and limitations of existing technologies. Knowledge in the first three areas is required for the development of useful sensors and their proper implementation in practice. Expertise in the last three areas is crucial for determining the type of information to be obtained, and how they should be interpreted to reflect the current condition of the structure or the material. With each member having strong technical background in one or more of the above areas, we expect to create a synergism within the committee that will facilitate the achievement of the various goals.

Detailed working programme

The work of the committee mainly involves the collection and synthesis of information to produce relevant documents and reports. While most of the communications can be conducted over the internet, it is crucial to hold committee meetings for discussions of the detailed work plan, determination of specific tasks and the assignment of responsibilities. There are two ideal venues for the committee meetings to be held. The first one is the SPIE Conference (organized by the International Society for Optical Engineering), held every March in San Diego. The second one is the Stuctural Health Monitoring Conference, held every summer or fall with its location alternating between the U.S. (at Stanford University) and Europe. As many of the committee members would be interested in attending one or both of these conferences, it will be convenient to have our committee meetings held in conjunction with these functions.

It is hoped that the first committee meeting can be held during the Structural Health Monitoring Conference in 2006. In this kick-off meeting, the scope of the committee’s work described in the present proposal will be reviewed and refined. The content of the State-of-the-Art report will be determined. While we expect all committee members to provide information for the report, several members will be assigned to take care of the coordination and writing of specific chapters. Also, for the document of case studies, we will decide on a specific template for the description of each case study. Each member can then provide information according to the template, and one of the committee members will serve as the coordinator to compile all the information into a comprehensive document.

We hope to have the State-of-the Art report completed within about 2 years’ time. At the time when the State-of-the Art report is completed, a workshop will be organized to focus on “Practical Applications of Fiber Optic Sensors in Civil Engineering”. In this workshop, presentations will be made to summarize the current state-of-the Art, and highlight applications where fiber optic sensors have been demonstrated to have clear advantages over conventional approaches. The paper presentations will be followed by discussions on specific sensing needs in civil engineering, and the potential of optical sensing in addressing such needs. The outcome of the workshop will be preliminary recommendations for the use of fiber optic sensors in practice. Based on these recommendations, we will start to work on the development of an Application Guideline for potential users of this technology. The Application Guideline should consist of two major parts. In the first part, we will address issues related to ‘When’ and ‘Why’ fiber optic sensors should be used. An introduction to various kinds of fiber optic sensors will be presented first (Note: the descriptions will be relatively brief here – for details, the reader can always refer to the State-of-the-Art report). Then, sensing needs in civil engineering are highlighted. Situations or applications where fiber optic sensors can beneficially replace conventional sensors will be discussed. After reading the first part of the guideline, the potential user should have an idea of whether fiber optic sensors are suitable for his/her particular application. The second part of the guideline will then cover more technical issues. For users who do not have much experience with this technology, we will present an introduction to major optoelectronic components required for optic fiber sensing, and the integration of these components into a practical sensing network. Issues such as precision, accuracy and reliability will be addressed. A number of examples will be given to illustrate how optical fiber sensing networks are set up for real structures. The development of the Application Guideline should involve significant discussions. Besides the meeting during the workshop, another committee will be organized about one year later to talk about the progress of the work.

Since optical fiber sensing is a relatively new technology, its application in civil engineering is expected to expand in the near future. We therefore would allow ourselves a bit more time to collect the case studies, and plan to finalize the document by the end of the third year. After that, a website on “Fiber Optic Sensing in Civil Engineering” will be created. In the site, we will provide introductions to optical sensing technology, and list relevant references for each sensing technique. Case studies illustrating the beneficial use of fiber optic sensors will be given. Also, links to other sites of interest will be set up. Committee members will take turn in maintaining the site. Information including new case studies and publications will be added to the site from time to time. Hopefully, this site will become a useful starting point for academics and engineers interested in adopting this technology in their research projects or applications.