Hysteresis Damping Behavior of Steel Frames with Collapse of Beam Subjected to Earthquake Ground Motion

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This research project studies the hysteresis damping behavior of steel frames with collapse of beam subjected to earthquake ground motion. Attention is paid to the collapse mechanism of portal frames with the collapse type of beam member1) The cumulative plastic strain of the column base parts, panel zones and column cross-section near panel zones decreases due to the shear collapse of web plates in beam. It should be noted that the strain rate of such shear panels in the plastic range is so high compared with that of column cross-sections.2) The numerical results demonstrate the fundamental plastic mechanism of frames with the shear collapse in the middle of beam and another collapse mechanism, which includes the shear yielding of panel zones in the beam-to-column connections. This mechanism is caused by the increase in shearing force due to strain hardening in the middle of beam.3) The partially tapered beam-columns subjected to cyclic bending can delays the occurrence of local buckling. The resulting damage is less than the uniform cross-section members and corresponding dissipated energy becomes larger with the increase in type ratio.4) The plastic bending deformation of the partially tapered sections set in beam near the beam-to-column connections can delay the increase in shearing force in beam. The resulting panel zones of connection remain almost elastic state.5) The decrease in the shear strength of web plates in beam eliminates the hysteresis damping effect corresponding to dissipated energy. It should be noted that the damage of column base parts and sway response of frames might become significant.