Optical Fiber Sensors and Conventional Sensors

Optical Fiber Sensors and Conventional Sensors

ABSTRACT

This study deals with the comparison of the two types of sensors which are widely used in civil engineering namely conventional sensors and optical fiber sensors Temperature and displacement are the two principal parameters which are measured with the aid of Fiber optic sensors Bragg Grating Interferometric Intensity Sensors and optical time domain reflectometry OTDR are some of the techniques which are used for sensing In this study various case studies have been undertaken and have been analyzed With the aid of these case studies a detailed analysis and comparison of the sensors is carried out

Chapter 1 INTRODUCTION

In the last two decades the world has witnessed a revolution in the sectors of optoelectronics and fiber optic communications Various products such as laser printers and bar code scanners which have become a part of our daily usage are a result of this technical revolution only The reasons for the phenomenal growth of the fiber optics are many The most conspicuous reason being the ability of the fiber optics to provide high performance and highly reliable communication links and that too at a very low bandwidth cost As we see that optoelectronic and fiber communications industry has progressed a lot and along with these industries fiber optic sensors have also benefited a lot from these developments Due to the mass production in these industries availability of fiber optic sensors at a low cost has been made possible in recent years With their availability at affordable costs fiber optic sensors have been able to enter the domain which was otherwise being ruled by the traditional sensors

In recent years the demand for the development of new materials to strengthen upgrade and retrofit existing aged and deteriorated concrete structures has increased rapidly The continuing deterioration and functional deficiency of existing civil infrastructure elements represents one of the most significance challenges facing the worlds construction and civil engineers Deficiencies in existing concrete structures caused by initial flawed design due to insufficient detailing at the time of construction aggressive chemical attacks and ageing of structural elements enhance an urgent need of finding an effective means to improve the performance of these structures without additionally increasing the overall weight maintenance cost and time In the last 50 years a large number of civil concrete structures have been built many of these structures particularly in offshore regions have now deteriorated and require repair in a short period of time

Moreover the increase of traffic volume and population in many developing countries is causing the demand to upgrade existing concrete structures to increase The damage of reinforced concrete RC structures through reinforcement corrosion and residual capacity are the most important issues that concern engineers These problems occur not only in constructed concrete structures but also in structures strengthened by externally bonded steel reinforcements

In the past the external steel plate bonding method has been used to improve strength in the tensile region of concrete structures with an epoxy adhesive and has proved to be successful over a period of 20 years However the use of steel reinforced plates and bars has its disadvantages including high corrosion rates which could adversely affect the bond strength and cause surface spalling of the concrete due to volumetric

change in the corroded steel reinforcements Since the early 1980s fibrereinforced plastic FRP materials have been used as a replacement for conventional steel materials for concrete strengthening applications In recent years the interest in utilizing FRP materials in the civil concrete industry in forms of rods plates grid and jacket has grown increasingly When an FRP plate with high tensile strength properties bonds on the concrete surface it can strengthen the structure with minimum changes to its weig

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