STRENGTH AND DUCTILITY OF UNEMBEDDED TYPE OF STEEL REINFORCED CONCRETE COLUMN BASE UNDER TENSILE FORCE

The unembeded type of the column bases of Steel Reinforced Concrete buildings were severely damaged by Hyougoken Nanbu Earthquake in 1995. The anchor bolts and main reinforcing bars were often broken. This is mainly due to the lack of consideration of the tensile force caused by the overturning moment during earthquakes. In this report the strength and ductility of the unembeded type of column bases are examined. The strength of a column base can be evaluated by the sum of the strength of the components unless the bond between the concrete and reinforcing bars is deteriorated. The large amount of tensile force deteriorates the ductility of the column base. We propose the formula to predict the ductility of the column base which relates the parameter "effective tensile force ratio" considering the bond strength as well as tensile strength.