This is the accepted version of the paper.This version of the publication may differ from the final published version. Abstract-This paper describes the design, commissioning, and evaluation of a fiber-optic strain sensor system for the structural health monitoring of a prestressed concrete posttensioned box girder railway bridge in Mumbai, India, which shows a number of well-documented structural problems. Preliminary laboratory trials to design the most appropriate sensor system that could be readily transported and used on site are described, followed by a description of load tests on the actual bridge undertaken in collaboration with Indian Railways and using locomotives of known weight. Results from the load tests using the optical system are compared with similar results obtained using electrical resistance strain gages. Conclusions are summarized concerning the integrity of the structure and for the future use of the sensor system for monitoring bridges of this type. Crack width measurements obtained during the load tests are also described. Permanent repository link

There is an ongoing need to measure strains in reinforced concrete structures more reliably and under a range of circumstances e.g. long term durability (such as effects of cracking and reinforcement corrosion), response to normal working loads and response under abnormal load conditions. Fibre optic sensors have considerable potential for this purpose and have the additional advantages, including of immunity to electromagnetic interference and light weight (Grattan et al, 2000). This is important in railway scenarios and particularly so when the lines are electrified. Their small size allows for easy installation. However, their use as commercial 'packaged' devices (traditionally seen as necessary to achieve adequate robustness) is limited by their high cost relative to other sensor devices such as encapsulated electric resistance strain gauges. This paper describes preliminary work to produce a cost-effective and easy-to-use technique for encapsulating fibre optic sensors in resin using 3D printing techniques to produce a robust, inexpensive 'packaged' sensor system suitable for use with concrete structures. The work done to date has shown this to be a convenient and economical way of producing multiple sensors which were suitable for both surface mounting and embedment in reinforced concrete structures. The proof-of-concept testing to which the trial packages were subjected is described in the paper and the results indicate that 3D printed packages have considerable potential for further development and use in a variety of civil engineering applications, competing well with more conventional sensor systems.

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This paper demonstrates the advantages of site monitoring to aid modelling of the existing condition of a railway bridge with structural problems and to assess the current structure and future remediation. The authors undertook monitoring and assessment on a major 28-span post-tensioned prestressed concrete box-girder bridge on a strategically important railway line in India. The bridge exhibited significant longitudinal web cracking, which restricted its load-carrying capacity to relatively light urban passenger rolling stock. Monitoring of rail traffic was supplemented by full-scale load tests for both static and dynamic loading. Optical strain sensors and electric resistance strain gauges were used for strain measurement and piezoelectric sensors were used to record accelerations. Sensors were also installed to record crack widths. A programme of numerical modelling was undertaken with finite-element models developed for both cracked and uncracked conditions. Results were compared with field data and the models were then refined to achieve a representative model for use as a predictive tool for future assessment and structural remediation of the bridge.

Fiber optic sensors have considerable potential for measuring strains in the challenging environment posed by today’s civil engineering applications. Their long-term reliability and stability are particularly important attributes for assessing, with confidence, effects such as cracking and response to normal (and abnormal) loads. However, given the fragile nature of the bare fiber, the sensors must be packaged to achieve adequate robustness but the resulting increased cost of installation can frequently limit the number of sensors which can be installed or their use may have to be ruled out altogether due to these financial constraints. There is thus potential for the development of a more affordable type of packaging and this paper describes work undertaken to produce a cost-effective and easy-to-use technique for encapsulating fiber optic sensors in resin, taking advantage of 3D printing techniques which are widely available and at low cost. This approach can be used to produce a robust, inexpensive packaged sensor system which is seen as being suitable to be extended to a wider range of uses including installation in concrete structures prior to casting. To evaluate this approach, several such 3D printed package types and geometries are described and their behavior is assessed from a programme of laboratory trials, the results of which are presented in this paper. This proof-of-concept testing has demonstrated the considerable potential which 3D printed packages have and the scope for further development and consequent use in civil engineering applications. Areas showing promise and potential, which have been identified from the work undertaken, are discussed.