10. Stability Checking System for Existing Concrete Structures

      In recent years, the age deterioration of concrete structures built during the period of high economic growth has become a public concern. In this study, an efficient, reliable integrated stability checking system attaching primary importance to operation at the site was developed Fig. 1 shows a conceptual diagram of the overall system. The arrangement consists of a measuring system made up of various non-destructive inspection devices and a support program, an evaluation system made up of various evaluation and checking programs, and a database to manage the above measurement/evaluation data.
      Field trials for the measuring system were performed using railway structures nationwide. In particular, the construction and standardization of a simple high-precision system was verified based on demonstration data including the following: verification of auto-recognition by image processing of cracks and standardization of photography methods, verification of the method of measuring concrete covers corresponding to extremely dense arrangement of bars specific to railway structures by the electromagnetic induction method (Fig. 2), verification of the neutralization measuring method using a drill and standardization of the measuring technique, and verification/standardization of the simple method of measuring salt content using a drill (Fig. 3).
      For this evaluation system, a range of programs was developed and verified in compliance with the Standard for Structure Maintenance and Management and the Design Standard for Railway Structures (concrete structures). In particular, various programs were developed for external force evaluations such as load equivalent value and equivalent number of repetitions, for durability evaluations such as neutralization, salt damage, and cumulative fatigue damage (Fig. 4), and for durability checking considering material deterioration for uniform stability evaluation.
      The above results will lead to more efficient and accurate inspection of concrete structures.

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