This paper presents the simplified approximate equation for the ultimate moment of reinforced concrete interior beam-column joint. The proposed equation is derived by extracting the main terms of the theoretical equation. The convergent calculation is omitted, and the branch conditions are simplified without significant loss of accuracy. The approximate equation is able to calculate not only the ultimate moment at both the beam and column rebar yielding but also that when the stress of the column rebar is given by the critical reinforcement.
