This paper is descraibed the occurrence tendency of cracks by corrosion of the PC sheath arranged in the PC structures. To investigate these, an experiment by electrically corrosion and numerical analysis by an FEM were performed.
 It is found that insufficiently grouted influences a crack of a PC by corrosion of a steel sheath. Therefore the consideration which imitated the insufficiently grouted situations assumed by existing structures was performed.
 It was proposed that insufficiently grouted investigation method in the PC structure which occurred due to corrosion of a steel sheath based on an obtained result.

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 Strengthening by external cables is often used in case it is necessary to recover or improve the load-carrying capacity of prestressed concrete girder. However, in the case of PC-I girder bridges with the narrow distance between adjacent main girders, the conventional anchorage units for external cables cannot be applied. Therefore, the authors proposed and developing a new anchorage unit.
 In this paper, loading tests were conducted to evaluate load-bearing mechanism and performance of the proposed anchorage unit. As a result of the tests, it was found that the anchorage unit showed small slip behavior at the interface between new and old concrete and rotating behavior before maximum loads and had large load-carrying capacity due to constraint effect. Also, the effects of the normal stress or the condition of interface or transverse girder on load-carrying capacity ware evaluated.

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