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

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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.