J. Leighton

City University London, Londinium, England, United Kingdom

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Publications (4)2.91 Total impact

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    ABSTRACT: The paper reports results obtained from an unusual situation in structural monitoring - a "test-to-destruction," measuring strain using a series of fiber Bragg gratings (FBGs) sensors on a decommissioned concrete Railway Bridge in Ornskoldsvik, Sweden. The study formed part of the EU "Sustainable Bridges" Project. To undertake the study, FBG-based sensors were chosen and embedded in carbon fiber reinforced polymers (CFRPs) composite rods incorporated into grooves specially created in the concrete structure and interrogated using a compact system based on wavelength-division multiplexing (WDM). Throughout the study, the FBG sensors were continuously monitored, allowing the incremental increases in the strain to be seen and through the yield point of the carbon composite reinforcement. The sensors were able to follow the resulting induced changes in strain of over a range in excess of 4000 muepsiv just prior to failure of the bridge and representing extreme levels of strain for such a mechanical structure. The measurements made with the FBG-based system were found to be in agreement with the changes expected in the structure (together with the embedded reinforcement), produced by the loading applied. The study has demonstrated the successful use of FBG-based technology premounted in "smart" carbon fiber composite reinforcements used in a test of this type on a typical bridge structure of a type found widely across the world.
    IEEE Sensors Journal 01/2009; · 1.48 Impact Factor
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    ABSTRACT: An all-fibre Tm:Ho laser system is reported, using a 1600 nm Er fibre pump laser and 0.3 m length of the fibre through a two-stage optimization of both the pump source and laser configuration to achieve a low threshold operation. As a result a low threshold power of 33 mW and a slope efficiency of 0.6% have been achieved, in laser operation at a wavelength of 1870 nm and a cross-comparison with 785 nm laser diode pumping has been made.
    Optics Communications 05/2008; 281(9):2567–2571. · 1.44 Impact Factor
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    ABSTRACT: This paper reports on the use of Bragg grating sensors for strain and temperature monitoring of reinforced concrete foundation piling. The use of optical fibre sensors on two reinforcing cages was made possible by the development of appropriate protection systems for the sensors. The cages were approximately 46 m long and 1.5 m in diameter. Sixteen Bragg grating sensors were bonded and protected by means of a carbon–fibre composite system in each reinforcing cage. The sensor protection systems were deployed successfully and all the fibre Bragg grating strain and temperature sensors survived the installation, transportation and subsequent filling of the foundation bores with concrete. The monitoring of the reinforcing cages during the pouring of the concrete into the borehole highlighted the presence of thermal tensile strains applied to the steel rebars because of the temperature of the liquid concrete. A change in the strain distribution along the whole depth of the foundation piles was observed half way through the concrete curing. A variation in the strain distribution was monitored due to the simultaneous effect of the construction of the building floors and the ground heave.
    Engineering Structures. 01/2007;
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    ABSTRACT: In this work, a 1600nm Er fibre laser, which demonstrates a high pumping efficiency, has been used to pump an efficient all-fibre Tm:Ho laser system using a 0.3 m length of optical fibre. A low threshold of 33 mW and a slope efficiency of 0.6% have been achieved with operation at a wavelength of ~1870 nm. A cross-comparison has been made with the output of a device pumped by a 785 nm laser diode. The focus of the work is better and more compact sources for gas sensing in the near infra red region of the spectrum.
    Journal of Physics Conference Series 01/2007; 76(1).