Experimental Study on Elasto-Plastic Behavior of Composite Steel and Reinforced Concrete Beam-Columns under Arbitrary Horizontal Force.

The elastic-plastic behavior of the composite steel and reinforced concrete(Abbreviated As SRC Hereafter)long beam-columns under the arbitrary horizontal force was investigated by the experiment，and compared with the analytical results。The built-up H-shaped steel encased in concrete has a cross section of H-50 x 50 x 3.2 x 3.2 mm。The longitudinal and transverse reinforcement arrangement were identical in all specimens and consist of 4&lt；phi&gt；bars.Experimental parameters selected for the investigation are as follows；1)Slenderness ratio(ratio of the beam-column length to the radius-of-gyration of concrete cross section)：20and50，2)Ratio of the axial load to the maximum axial strength：0，0.2 and 0.33，3)Direction of the horontal load：0，22°。1)The maximum carrying capacity of a short SRC beam-column is determined by the crash of concrete，and that of a long beam-column by the instability。2)The value of the biaxial bending moment capacity of a long SRC beam-column computed at the maximum horizontal load is smaller than the value given by the interaction obtained from the ultimate strength theory，while that of a short beam-column reaches the interaction curve。3)When the flexural stiffnesses of the beam-colum are fifferent in two principal axes as observed in the present test，the increment of the displacement corresponding to the strong axis bending slows down，and eventually starts decreasing because of P&lt；DELTA&gt；-moment。Finally，the beam-column seems to shift to the condition of the uniaxial bending.4)An abrupt failure occurrs when the increment of the displacement corresponding to the strong axis bending becomes neally zero.

The elastic-plastic behavior of the composite steel and reinforced concrete(abbreviated as SRC hereafter)long beam-columns under the arbitrary horizontal force was investigated by the experiment, and compared with the analytical results. The built-up H-shaped steel encased in concrete has a cross section of H-50x50x3.2x3.2mm. The longitudinal and transverse reinforcement arrangement were identical in all specimens and consist of 4 <phi> bars.Experimental parameters selected for the investigation are as follows; 1) Slenderness ratio( ratio of the beam-column length to the radius-of-gyration of concrete cross section ): 20 and 50, 2) Ratio of the axial load to the maximum axial strength: 0, 0.2 and 0.33, 3) Direction of the horizontal load: 0゜, 22.5゜ and 45゜.The obtained results are summarized as follows; 1) The maximum carrying capacity of a short SRC beam-column is determined by the crash of concrete, and that of a long beam-column by the instability. 2) The value of the biaxial bending moment capacity of a long SRC beam-column computed at the maximum horizontal load is smaller than the value given by the interaction obtained from the ultimate strength theory, while that of a short beam-column reaches the interaction curve. 3) When the flexural stiffnesses of the beam-colum are fifferent in two principal axes as observed in the present test, the increment of the displacement corresponding to the strong axis bending slows down, and eventually starts decreasing because of P <DELTA> -moment. Finally, the beam-column seems to shift to the condition of the uniaxial bending. 4) An abrupt failure occurrs when the increment of the displacement corresponding to the strong axis bending becomes neally zero.