Structural Health Monitoring (SHM) is a procedure of evaluating the in-service performance of structures, assessing the changes in the structural performance profile over a period of time, and aiding in decision making process for optimized maintenance and management of the structure during its life cycle. For strain measurement of civil infrastructure, Fiber Optic Sensors (FOS) are found to be useful for their durability and accuracy. They are known to be significantly more advantageous over conventional electrical strain gauges. However, special care and protection are needed for the installation of FOSs in reinforced concrete structures because of their delicate nature. To mitigate the difficulty in installing and embedding FOS in reinforced concrete structures, it has been proposed previously and developed in the present study that it is pre-installed in a supplemental bar which can be attached to the main reinforcement in a reinforced concrete structure in order to capture the strain in the structural elements. However a number of parameters such as the length, relative diameter of the supplemental bar as compared to the main bar, and the attachment mechanism between the main and supplemental bars can affect the performance of such systems. The purpose of the study is to characterize such bars, for their ability to transfer the strain of the main reinforcements appropriately for the use of engineering analysis. An experimental study involving tension tests of reinforcing FRP bars with FOS embedded supplemental bars attached to them is conducted to identify the appropriate size, length and attachment method of the supplementary bars in terms of the strain experienced by the supplementary bars as compared to the real strain values of the corresponding main bars. A number of specimens with different combinations of the governing parameters as mentioned earlier are utilized in the test. Some of the specimens were confined in concrete cylinders to study the effect of such confinement in the performance of the proposed system. Adequate number of specimens were built and tested to assure the reliability of the tests, and the preliminary results indicate that the proposed system is viable, cost effective and practical. The results showed that in all cases, supplementary bars with two development length had closest strain capture of the main bar while the proposed attachment method could assure proper strain transfer. Moreover the study revealed that the less the diameter of the supplementary bar is chosen, the better results will appear. In the next step of the study a set of FRP reinforced concrete beams were constructed with the proposed FRP protected FOS systems, and the beams were tested in flexure to study the performance of the proposed protection mechanism for FOS in full scale reinforced concrete components.
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