The employment of confined concrete with circular reinforcement in the compression zone of concrete flexural members improves the ductility of those members so significantly. Therefore, the mechanical properties of the confined concrete should be revealed in order to establish a ductility design method for designing advanced asseismic concrete structures.
The objects of this study, in which different experimental variables were adopted from those used in other researches, were to investigate the strength and deformation characteristics of concrete confined by lateral circular reinforcement and to establish the equations for evaluating the compressive strength (Fcf), corresponding strain (ε0, cf) and average gradient of falling branch in the region from ε0, cf to 2ε0, cf of the confined concrete (Ecf). The variables considered were the magnitude of average confining stress (psσsy), the ratio of pitch of circular reinforcement to the diameter of specimen (S/D) and concrete strength (F0). The main results obtained are as follows.
(1) The equations for estimating the values of the above-mentioned characteristics were established by clarifying the effects of S/D, psσsy, and F0 on those characteristics.
(2) In order to obtain yielding of circular reinforcement, the value of S/D should be less than about 0.7 irrespective of the values of psσsy and F0.
(3) The examination of feasibility of those induced equations, based on the experimental data about the scale effect of confined concrete as well as those presented by other researchers, shows that the proposed equations can be used to estimate the values of Fcf, ε0, cf and Ecf very successfully.