MINIMISATION OF STRUCTURE LIFETIME COST THROUGH PROVISION OF A TWO STAGE ASSESSMENT PROCESS

Abstract eng:
Inspection based maintenance strategies can provide an efficient tool for the management of ageing bridge structures subjected to deterioration. Many of these methods rely on quantitative data from inspections, rather than qualitative and subjective data. The main focus of this paper is on the development of an inspection based decision scheme, incorporating analysis on the effect of the cost and quality of NDT tools to assess the condition of a bridge structure over its lifetime. Two aspects of an inspection are considered, detection and sizing. In this study a distinction has been made between an inspection carried out to detect a defect, and an inspection carried out to size a defect. Since each stage of an inspection is carried out for a distinct purpose, different parameters are used to represent each procedure and both have been incorporated into a maintenance management model. The separation of these procedures allows the interaction between the two inspection techniques to be studied. This allows an optimal maintenance management plan to be developed by choosing the most suitable inspection technique for each stage of the inspection, whether it is for detection or sizing, rather than using the same inspection technique for both procedures. As part of the process the first part of an inspection is concerned with the detection of existing defects. The Probability of Detection (PoD) and the Probability of False Alarm (PFA) are used in this study, for a particular NDT tool used in the assessment, to indicate the quality of the inspection method for detection. The second part of an inspection deals with the assessment of the size of the defect knowing that it has already been detected. For this part of the analysis, two new parameters are introduced, Probability of Good Assessment (PGA) and Probability of Wrong Assessment (PWA). By varying the quality of the inspection techniques separately, the optimum combination of techniques can be determined. A decision tool is developed, which allows the owner/manager of a bridge structure to choose the most cost efficient maintenance management plan based upon his/her specific requirements.

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