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.

Structural health monitoring based maintenance (SHMBM) is a basic engineering effort to collect maintenance information, forming a database system to open to the public or citizens for making decision on a suitable solution strategy to extend a structure's life. Sustainability of the infrastructure structural performance can be assessed by performing continuous structural health monitoring system (SHMS) on the structural deformational properties. The essence of SHMS can be considered to involve measurement, inspection, and assessment of in‐service structures on a continuous basis with minimum labor requirement. However, human memory limitation, job changes, imperfections and inability to provide a reliable monitoring system can lead to overly optimistic reports on structural health. Therefore, a sustainable SHMS which fulfill ‘AtoE’ characteristics, i.e. accuracy, benefit, comprehensiveness, durability and ease of operation, is necessary to be consider in designing a reliable long‐term SHMS. Generally, those characteristics are difficult to compare quantitatively. Specifically, some qualitatively compared sensory technologies will be reviewed in this paper by comparing the application of load cell, stress meter, strain gauge and EM (elastomagnetic) sensory technology. Furthermore, some innovative sensory technologies such as GPS‐based MMS (movement monitoring systems), PDMD (peak displacement memory devices) and FOS (fiber optic sensors), are introduced to monitor global structural movement, partial structural movement and local structural deformational properties at different scales of monitored objects. Copyright © 2005 John Wiley & Sons, Ltd.

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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.