This paper proposes a new simpli ed restoring force characteristic model of a shearing force-rotation angle relationship for concrete-lled square steel tube beam-columns from short to slender. In the proposed model, each exural strength is calculated by a general superposed strength method, and new multiple regression formulas for each rotation angle are proposed based on results of monotonic and cyclic loading tests from previous researches. Predictions from the model of the shearing

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... tion angle relationship are found to agree approximately with experimental results up to large rotation angles.