A Study on the Unstable Behavior of H-Shaped Steel Beam-Columns Subjected to Multi-Dimensional Loads

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Beam-columns of multi-story frames are subjected to biaxial bending moment due to horizontal forces acting on the columns in two directions during an earthquake. There are many unclear points on unstable behavior of H-shaped steel beam-columns subjected to biaxial bending moment. Members with a relatively small slenderness ratio can absorb plastic energy while gradually increasing lateral torsional deformation after yielding, but there have been few study experiments on such a case. This study aims at obtaining the basic data required to establish a method for quantitatively estimating the energy absorption ability through making clear the type of collapse for H-shaped steel beam-columns as well as basic parameters determining the energy absorption ability.In the experiments, the bending moment was loaded by acting a horizontal force in a direction with an angle from the principal axis of the section. The values for the angle were set as 0 (strong axis bending moment), 30, 60, 90 degre … More es (weak axis bending moment). The experiment variables were set as slenderness ratio, axial ratio, horizontal force loading direction (the angle) and loading method (nionotonic loading or cyclic loading).The results of this study can be summarized as follows :1) The results of analyses correspond well to the experiment results. The validity of the analytical method used in this study was confirmed.2) With regard to the member deformation condition at the ultimate stage, three patterns for the lateral deformation and torsional deformation were observed.3) All specimens subjected to an oblique load (the angle=30, 60 degrees) torsionally collapsed in such a state as the web axis approaches a direction at a right angle to the loading direction at the longitudinal center of the member.4) The skeleton curve on positive and negative sides obtained from the cyclic loading curve for the specimen (the angle=0 degrees) subjected to strong axial bending moment was lower than the monotonic loading curve. The skeleton curve for the other specimens (the angle=30, 60, 90 degrees) was almost equivalent to the monotonic loading curve.5) The relationship between the conditions for both the specimen and the loading and the amount of the energy absorption was obtained. Less