Design method for steel framed members with variable cross-section considering inelastic earthquake response

本课题对变截面门式刚架的弹塑性地震反应进行了数值模拟和试验研究。(1)试验研究：(1)进行了六个变截面框架试件在恒定竖向荷载和交变水平荷载作用下的破坏试验。(3)对试验结果进行了整理，并与数值计算结果进行了比较。(2)为了考虑梁柱节点和梁心附近的弹塑性性能，推导了腹板在剪力作用下的传递矩阵。定义了柱和节点的概念，对框架的倒塌模式进行了分类。3)仅在柱的中部截面发生塑性变形的倒塌模式是不利的，4)梁的中心部分由于抗力较小，不能在不造成严重损伤的情况下起到消能的作用。5)梁中心的塑性依赖于梁的跨柱高比。6)日本南方地震中钢框架桥墩的梁中心的损伤与变截面梁与板区抗力的差异密切相关。7)门式刚架的有利倒塌模式是限制梁柱底部和梁板区域的塑性变形。8)变截面设计的基本思想是在具有较大抗力结果的截面上耗能，如柱脚、柱脚和板区。

This project studies the inelastic earthquake response of steel portal frames with variable cross-section numerically and experimentally. The conclusions can be summarized as follows :(1) Experimental study1) Six test specimens for variable cross-section frames were tested up to failure under the condition of constant vertical and alternating horizontal loads.2) The three different collapse modes appeared due to the variable cross-section.3) These test results were arranged to compare with the numerical results.(2) Numerical study1) Transformation matrix of web plates in shear is derived in order to consider the elasto-plastic behavior of beam-to-column connections as well as the vicinity of the center of beam.2) Some appropriate parameters with respect to yielding of beam, columns and connections are defined to classify the collapse modes of frames.3) The collapse mode with the plastic deformation only within the middle cross-section of columns is unfavorable, because the significant cumulative plastic strain leads to the local buckling.4) The center part of beam cannot aid in energy dissipation without heavy damage due to the small resistance force.5) The plasticity of the center of beam depends on the beam span-column depth ratio.6) the damage at the center of beams of steel framed piers in Hyogoken-Nanbu Earthquake is highly related to the difference between the resistance forces of beams with variable cross-section and panel zones.7) The favorable collapse pattern of portal frames is to restrict the plastic deformation within the column base part and panel zones of beam-to-column connections.8) The fundamental idea for designing the variable cross-section is to dissipate energy in the cross-section with large resistant stress-resultants such as column base barts and panel zones.