抄録
Application of confined concrete to the compression zone of reinforced concrete columns is very useful to improve flexural ductility of the columns. However, equations to estimate confining reinforcement necessary for flexural ductility required are not established sufficiently.
In this paper, the amount of confining reinforcement to give flexural ductility requirement to the columns are investigated. The main results obtained are as follows.
1) The equation (4) to calculate the required confining reinforcement ratio (ptr) was derived from the analytical investigation and examination on the previous experimental data as for the effects of various factors on ptr. The factors employed in the investiation were the rotation angle required in plastic hinges, the axial force ratio, the material properties such as concrete strength and the ratio of core area to the whole area of column sections.
2) Examination of eq. (4) indicates that (a) the ultimate rotation in plastic hinges (θu) calculated by eq. (4) is more conservative than the ultimate rotation angle of members (Ru) obtained by test columns. (b) Ru of columns failed in shear is smaller than θu, estimated by eq. (4), and (c) NZS code tends to recommend rather large confining reinforcement under low axial force ratio and rather small one under high axial force ratios.
