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The rapid expansion of the optical fiber telecommunication industry due to the explosion of the Internet has substantially driven down the cost of optical components, making fiber optic sensors more economically viable. In addition, the rapid development of fiber-optic sensors, particularly the fiber Bragg grating (FBG) sensors offers many advantages and capability that could not be achieved otherwise. In the past few years, fiber Bragg grating sensors have attracted a lot of interest and they are being used in numerous applications. This paper describes the FBG sensors developed for structural health monitoring, and were installed on Hong Kong's landmark Tsing Ma bridge (TMB), which is the world longest (1377 m) suspension bridge that carried both railway and regular road traffic. Forty FBG sensors divided into three arrays were installed on the hanger cable, rocker bearing and truss girders of the TMB. The objectives of the study are to investigate the feasibility of using the developed FBG sensors for structural health monitoring, via monitoring the strain of different parts of the TMB under both the railway and highway loads as well as comparing the FBG sensors' performance with the conventional structural health monitoring system - Wind and Structural Health Monitoring System (WASHMS) that has been operating at TMB since the bridge's commissioning in May 1997. The experimental observations in this project show that the results using FBG sensors were in excellent agreement with those acquired by WASHMS. © 2005 Elsevier Ltd. All rights reserved.

The rapid expansion of the optical fiber telecommunication industry due to the explosion of the Internet has substantially driven down the cost of optical components, making fiber optic sensors more economically viable. In addition, the rapid development of fiber-optic sensors, particularly the fiber Bragg grating (FBG) sensors offers many advantages and capability that could not be achieved otherwise. In the past few years, fiber Bragg grating sensors have attracted a lot of interest and they are being used in numerous applications. This paper describes the FBG sensors developed for structural health monitoring, and were installed on Hong Kong's landmark Tsing Ma bridge (TMB), which is the world longest (1377 m) suspension bridge that carried both railway and regular road traffic. Forty FBG sensors divided into three arrays were installed on the hanger cable, rocker bearing and truss girders of the TMB. The objectives of the study are to investigate the feasibility of using the developed FBG sensors for structural health monitoring, via monitoring the strain of different parts of the TMB under both the railway and highway loads as well as comparing the FBG sensors' performance with the conventional structural health monitoring system - Wind and Structural Health Monitoring System (WASHMS) that has been operating at TMB since the bridge's commissioning in May 1997. The experimental observations in this project show that the results using FBG sensors were in excellent agreement with those acquired by WASHMS. © 2005 Elsevier Ltd. All rights reserved.

Historically, due to the high cost of optical devices, fiber-optics sensor systems were only employed in niche areas where conventional electrical sensors are not suitable. This scenario changed dramatically in the last few years following the explosion of the Internet which caused the rapid expansion of the optical fiber telecommunication industry and substantially driven down the cost of optical components. In recent years, fiber-optic sensors and particularly fiber Bragg grating (FBG) sensors have attracted a lot of interests and are being used in numerous applications. We have conducted several field trials of FBG sensors for railway applications and structural monitoring. About 30 FBG sensors were installed on the rail tracks of Kowloon-Canton Railway Corp. for train identification and speed measurements and the results obtained show that FBG sensors exhibit very good performance and could play a major role in the realization of "Smart Railway". FBG sensors were also installed on Hong Kong's landmark TsingMa Bridge, which is the world longest suspension bridge (2.2 km) that carries both trains and regular road traffic. The trials were carried out with a high-speed (up to 20 kHz) interrogation system based on CCD and also with a interrogation unit that based on scanning optical filter (up to 70 Hz). Forty FBGs sensors were divided into 3 arrays and installed on different parts of the bridge (suspension cable, rocker bearing and truss girders). The objectives of the field trial on the TsingMa Bridge are to monitor the strain of different parts of the bridge under railway load and highway load, and to compare the FBG sensors' performance with conventional resistive strain gauges already installed on the bridge. The measured results show that excellent agreement was obtained between the 2 types of sensors.

Sensors for strain measurement are indispensable for structure monitoring. Fiber optic sensors based on Fiber Bragg Grating (FBG) technology are found to be suitable for strain sensing and have a number of advantages compared to conventional strain gauges. Recently, we carried out a field trial with a FBG sensor array system on the world’s longest span suspension bridge carrying both trains and regular road traffic (The Tsing Ma Bridge in Hong Kong). The experiment was carried out with a high-speed dense-channel demultiplexing/interrogation system for FBG sensor arrays (DC to ~20 kHz for all channels simultaneously). This system is originally developed for the detection of high-speed events (vibration, impact location and acoustic emission), but in this field experiment the high readout frequency has been used for noise reduction by averaging to achieve sub-pm resolution. More than 20 FBG sensors divided into 3 arrays were installed on different parts of the bridge (suspension cable, rocker and frame section). The goal of this field trial is to monitor the strain of the different parts of the bridge under railway load and highway load. Various measurements were performed including an overnight measurement of about 20 hours with a sampling frequency of about 500 Hz. The measurement results reveal the presence of significant higher frequency components in the FBG sensor signal during train passages. The results of the FBG sensor also compared with existing strain gauges. Although the sensors are not located at exactly the same location, great resemblance has been found.

In this paper, we present the results of the 'trial-test' of using fiber Bragg grating sensors to monitor the dynamic strain and temperature of Tsing Ma Bridge. Sensor packaging, installation technique as well as comparison of the measurement results of FBG sensors and electrical strain gauge sensors will be discussed.