抄録
Accurate and easy calculation of the ultimate flexural strength (Mu) of reinforced concrete (RC) columns is necessary to design the columns under flexural moment, axial force and shear force.
In this paper, the following results are obtained from investigation on the ultimate flexural strength Mu.
(1) Stress block coefficients κ1κ3 and κ2 at the maximum value of κ1κ3 were indicated to be useful for calculating Mu in RC columns. These two coefficients denote the ratio of the average stress of stress-strain curve up to an arbitrary strain to the compressive strength and the ratio of the strain at the location of center of gravity of the corresponding area to the arbitrary strain, respectively.
(2) Equations to estimate the coefficients κ1κ3 and κ2 for calculating Mu were derived from the examination of the two coefficients, based on the stress-strain relations proposed previously for plain concrete and confined concrete.
(3) Equations to calculate Mu, in which confined concrete in the compression zone and intermediate longitudinal reinforcement of the column sections are considered, were derived under the assumption of the use of the coefficients κ1κ3 and κ2, as well as the yielding of each longitudinal reinforcement in tension or compression. The evaluation of the previous experimental results of the ultimate flexural strength Mu by these equations gave about 10 percent smaller values on an average than the experimental ones, irrespective of axial load magnitude.
