Monitoring based maintenance utilizing actual stress sensory technology

Abstract

In recent years, many infrastructures have been deteriorating. In order to maintainsustainability of those infrastructures which have significant influence on social lifelines,economical and rational maintenance management should be carried out to evaluate the lifecycle cost (LCC). The development of structural health monitoring systems, such asderiving evaluation techniques for the field structural condition of existing structures andidentification techniques for the significant engineering properties of new structures, can beconsidered as the first step in resolving the above problem. New innovative evaluationmethods need to be devised to identify the deterioration of infrastructures, e.g. steeltendons, cables in cable-stayed bridges and strands embedded in pre- or post-tensionedconcrete 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 ofincremental magnetic permeability to stress change, has been developed. Numerousverification tests on various steel materials have been conducted. By comparingwith load cell, strain gage and other sensory technology measurement results,the actual stresses of steel tendons in a pre-stressed concrete structure at thefollowing stages have been thoroughly investigated: (i) pre-stress change due toset-loss (anchorage slippage) at the tendon fixation stage; (ii) pre-stress changedue to the tendon relaxation stage; (iii) concrete creep and shrinkage at the longterm 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 ofthis testing, it is confirmed that EM sensory technology enables one to measureactual stress in steel wire, strands and steel bars precisely without destroying thepolyethylene covering sheath and enables one to provide adequate accuracy andreliability for monitoring actual stresses of those steel tendons during the life cycle ofinfrastructures. An example of a field application at a cable-stayed bridge is described.