Failure Mode of Columns of Existing R/C Building Damaged During the 2007 Niigata Chuetsu-Oki Earthquake

The school building investigated was a 3-story reinforced concrete (R/C) building built in 1963. The building suffered from a great deal of damage during both the 2004 Chuetsu Earthquake and the 2007 Chuetsu-Oki Earthquake. The damage of the first and second floors during Chuetsu Earthquake was light and that by Chuetsu-Oki Earthquake was moderate. The previous study revealed that the anticipated design failure modes of most of the columns of the building were flexure although most of them actually failed in shear during the 2007 earthquake. This is an important problem to be studied. In order to study the reason why the columns failed in shear rather than in flexural, a parametric study was conducted, paying attention to parameters including the strength of concrete, hoop spacing and subjected axial force. But those studies could not explain the real phenomenon clearly. After that the effects of cutoff location of longitudinal reinforcement bars were examined and it was concluded that the diagonal crack generated from cutoff point caused shear failure in these columns.