In recent years, many infrastructures have been deteriorating. In order to maintain sustainability of those infrastructures which have significant influence on social lifelines, economical and rational maintenance management should be carried out to evaluate the life cycle cost (LCC). The development of structural health monitoring systems, such as deriving evaluation techniques for the field structural condition of existing structures and identification techniques for the significant engineering properties of new structures, can be considered as the first step in resolving the above problem. New innovative evaluation methods need to be devised to identify the deterioration of infrastructures, e.g. steel tendons, cables in cable-stayed bridges and strands embedded in pre-or post-tensioned concrete structures. One of the possible solutions that show 'AtoE' characteristics, i.e., (a)ccuracy, (b)enefit, (c)ompendiousness, (d)urability and (e)ase of operation, elasto-magnetic (EM) actual stress sensory technology utilizing the sensitivity of incremental magnetic permeability to stress change, has been developed. Numerous verification tests on various steel materials have been conducted. By comparing with load cell, strain gage and other sensory technology measurement results, the actual stresses of steel tendons in a pre-stressed concrete structure at the following stages have been thoroughly investigated: (i) pre-stress change due to set-loss (anchorage slippage) at the tendon fixation stage; (ii) pre-stress change due to the tendon relaxation stage; (iii) concrete creep and shrinkage at the long term pre-stressing stage; (iv) pre-stress change in the cyclic fatigue loading stage; and (v) pre-stress change due to the re-pre-stress setting stage. As the result of this testing, it is confirmed that EM sensory technology enables one to measure actual stress in steel wire, strands and steel bars precisely without destroying the polyethylene covering sheath and enables one to provide adequate accuracy and reliability for monitoring actual stresses of those steel tendons during the life cycle of infrastructures. An example of a field application at a cable-stayed bridge is described.
Elasto-Magnetic ( E M) actual-stress measurement method by utilizing the sensitivity of incremental magnetic permeability due to stress change has been being developed. Previously, it has been proved that E M measurement method enable to measure actual-stress of steel wire, PC bar and PC strand contactlessly without destroying their polyethylene covering sheath. Furthermore monitoring tensile force of PC tendon is the most important issue in PC structure maintenance management. Therefore, in this paper, in order to grasp the reliability of E M sensor for field-application purpose, a test of tensile force monitoring on PC tendon of outer cable PC beam by utilizing E M sensor was conducted. As the result of the test, it is conformed that E M stress measurement technology can provide adequate accuracy and reliability to monitor tensile force of PC tendon during a life-cycle of PC structure.
The problems related to concrete structure maintenance can be indicated as unavailableness of (i) precise and economical monitoring system and (ii) safe and durable repair and retrofit engineering construction method. In recent years, early-strength, freezing-thawingt-resistance, high-durable and easy thickly-spray shotcrete has been developed. In this research, optical fiber sensory technology was utilized to monitor the deformational properties of shotcrete-retrofitted RC beams . Previously, the reliability and stability of the optical fiber sensory system has been verified by examining the steel expansion coefficient of a steel plate. By investigating crack propagation characteristic, it is confirmed that thefiber sensory technology can be applied to grasp the deformational behavior of retrofitted RC structures .
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