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

本课题研究地震作用下梁倒塌的钢框架的滞回减震性能。1)由于梁中腹板的剪切倒塌，柱脚部位、板区和板区附近柱截面的累积塑性应变减小。值得注意的是，这种剪力板在塑性范围内的应变率比柱截面的应变速率要高得多。2)数值计算结果表明，框架的基本塑性机理是梁中部发生剪切倒塌，另一种倒塌机理是梁柱连接节点中板区的剪切屈服。这一机理是由于梁中部应变硬化导致剪力增大所致。3)局部变截面梁柱在循环弯曲下可以延缓局部屈曲的发生。梁的损伤小于等截面构件，相应的耗能随型式比的增大而增大。4)梁柱节点附近设置的部分变截面的塑性弯曲变形可以延缓梁的剪力增长。5)梁腹板抗剪强度的降低消除了与耗能相对应的滞回阻尼效应。值得注意的是，柱脚部分的损伤和框架的摇摆反应可能会变得很严重。

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.