Abstract
The experimental study is carried out for the purpose of studying the restoring force characteristics, ductility factor and spring constant of reinforced concrete portal frames in case of the variation of axial compression stress (σ_c=0〜120kg/cm^2) in column. The models are nearly as large as magnitude of one-eighth of the actual buildings. The modeles become to be shear failure with the increase of the axial compression force in column. The restoring force characteristics is bi-linear type for column subject to the axial force equal to zero, and is nearly leminiscate curve (double-spindele) type with the increase of the axial compression force in column. Ductility factor, R, the ratio (δ_r/δ_y) and the ratio (σ_c/F_c) lie in a linear relation in logarithmic co-ordinate and they have a decreasing tendency with the increase of the axial compression force in columns. The ratio (k_2/k_1) have a tendency to enlarge with the increase of the axial compression force in column. If the ratio (k_2/k_1) is replaced by a parameter such as n=1-k_2/k_1, n gradually decreases with the increase of the axial compression force in column. NOMENCLATURE; ductility factor (δ/δ_y) R; joint translation angle; residual displacement; yield displacement; axial compression stress in column; 28-days concrete strength; spring constant in elastic ragne; spring constant in plastic range
