Practical Research Work on Diagnosis and Strengthening for ASR Deteriorated Bridge Piers with Fracture of Steel Reinforcement

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Research results obtained in this study are summarized as follows ;(1)Investigation on fracture of steel bars in ASR-affected structuresResearch works revealed that the embrittle fracture of steel bars at the bending corner of stirrup or bent-up steel bars, due to excessive expansion of concrete due to ASR, occurred in the pillow beam or footing of piers and the abutment in bridges located in Ishikawa Prefecture, leading to the significant loss of structural integrity of concrete elements.(2)Mechanisms of fracture of steel bar due to ASRIn the pillow beam or foundation of bridge pier, a lot of stirrup steel bars fractured at the bending corners, without any elongation of steel bar. The fracture surface of steel bar seemed to be very flat and smooth, which indicated the typical embrittlement fracture of steel bar. Whether or not the fracture of steel bars may be associated with the stress corrosion cracking and/or the hydrogen embrittlement fracture was discussed.(3)Asset management for ASR-deteriorated bridgesFor all bridge piers located in Ishikawa prefecture, which is considered to be the most serious ASR case in Japan, the degree of deterioration of bridge pier due to ASR was investigated by the visual inspection of cracking. Corresponding to the classification of ASR deterioration level of each bridge pier, the repair/strengthening method and maintenance procedure were proposed.(4)Strengthening and monitoring of ASR-deteriorated bridge piersIn the case study of the pillow beam of Kashima Bridge and the foundation of Tokuda No.2 Bridge in Ishikawa Prefecture, the degree of deterioration of bridge pier due to ASR was also investigated by the non-destructive inspection. Based on the classification of ASR deterioration level of each element, the most appropriate strengthening methods were adopted for them. In the maintenance of these bridges, the monitoring using crack sensors was successfully applied in order to ensure the daily safety of these bridges.