抄録
An experimental study are made of the effects of vertical loads on the behavior of steel portal frames subjected to horizontal loads. A specimen is composed of two similarly made miniature rigid portal frames, both being connected to each other in order to prevent lateral buckling of the frame. A frame is cut out by a machine from a mild steel plate stockwith 10mm thickness. The span and column height are chosen to be 200mm. The elastic flexural rigidity of the beam is either equal to or half that of the columns. 100, 50 and 30 are adopted as the ratios of the column height to its radius of gyration. Constant vertical loads are applied by hydraulic jacks at the tops of the columns symmetrically ; the loads are 0%, 10%, 20% and 40% of the elastic or the tangent modulus buckling load of a frame due to vertical loads only. A varying horizontal load is applied slowly by a testing machine to one direction of beam axis. It is observed that the shape of the horizontal load-displacement curve greaty depends on the magnitude of the vertical loads. The slope of the curve decreses as the horizontal load increases ; when the vertical loads are large the slope becomes negative after a certain displacement is reached. As the vertical loads increase, the maximum horizontal load decreases and the stability lilmit displacement also decreases. Experimental behavior is fairly well predicted by elastic-plastic analysis based on the true stress-strain relations of materials.
