Synopsis: By analysis of the data of periodic inspections of national highway bridges in Japan, the actual condition of concrete members and the characteristic of degradation were clarified. Many concrete girders have a cracked skin, which is conjectured to have occurred soon after the completion of construction. Moreover, the data showed that the kind of cracked skin that tends to occur differs for pre-tensioning girders and post-tensioning girders. Furthermore, it became clear that degradation speed differs for differing forms of the component section. Multiple linear regression analysis was conducted using many form-related items, such as the environment conditions, the bridge types and the applied design criteria. Notwithstanding, the results did not allow identification of the dominant factor that influences the degradation characteristics.

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