抄録
Splitting bond failure along the longitudinal deformed rebars has been often observed in the experiments of reinforced concrete columns with shear span ratio of around 1.5 to 2.5 subjected to antisymmetric cyclic bending shear. This failure reduces the seismic ductility and energy dissipating capacity of the column. Proposed design criteria is shown in Fig. 1 and Eq. (1). Effective development length Z is calculated by Eq. (3). The plastic region length α is calculated by Eq. (5), where R is the deflection angle amplitude. Normalized bond strength is defined by Eq. (4). Bond ductility, which is defined as a bearing capacity of bond stress at large slip, is neglected within the proposed criteria. Columns with different axial forces and with various web reinforcing ratios, bond strengths and bond ductilities, were analyzed by the method proposed by the author (21, 22). Following conclusions were obtained. (1) There exists a definite correlation between the normalized bond strength and the energy dissipating capacity of the column, almost regardless of the amount of the axial force or the bond ductility. (2) The resisting force of the column after the reversed cyclic loading, is affected by the normalized bond strength as well as the bond ductility or the amount of the axial force. However, if the normalized bond strength is unity, the resisting force after the cyclic loading becomes equivalent to the virgin strength, regardless of the bond ductility. (3) The slip at the midspan of the column can not necessarily be less, as the bond capacity (strength or ductility) be made larger. In the column where the yielding of the main bar occurs only in the positive loading and not in the negative loading, the slip at the midspan is larger than that in the column where the bond capacity is smaller and the yielding of the main bar does not occur both in the positive and negative loading. (4) The slip at the midspan the column is affected by the normalized bond strength as well as the bond ductility. However, if the normalized bond strength is unity, the midspan slip can be small enough to make the ratio of the deflection component due to the midspan slip to the deflection amplitude less than one-tenth, regardless of the bond ductility.
