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Seismic Behavior of Deep, Slender Wide-Flange Structural Steel Beam-columns


This thesis investigates nonlinear cyclic responses of deep wide-flange steel beam-columns, which are primarily used in Special Moment Frame (SMF) for their high in-plane, strong-axis moment of inertia to satisfy story drift limits specified in building codes. SMF design principles aim to achieve energy dissipation through plastic hinging of the beams, while flexural yielding of the columns at the base is also permitted. Although behavior of the beams has been extensively researched, that of the columns is lacking especially for deep columns (e.g., W18 to W36). Therefore, cyclic testing of deep columns was conducted to generate experimental database. Due to large width-to-thickness ratios of these sections, test results showed significant web and flange local buckling; some specimens also exhibited lateral-torsional buckling. These local and global instabilities resulted in significant axial shortening and flexural strength degradation. These behaviors differ significantly from those observed in prior testing of shallow W14 columns, featuring excellent ductility capacity at high axial loads.

Additionally, the test matrix was designed to investigate the effects of section depths, varying axial loads, lateral-drift loading sequences, and boundary conditions on the column responses. Inevitably in this testing, the responses were also influenced by flexibility of column-end connections. To eliminate this undesired variable from the responses, a procedure was developed to correct the lateral drift response based on the second-order Timoshenko elastic theory. The effects of boundary conditions were further investigated using high-fidelity finite element software ABAQUS. Results show that fixed-fixed and fixed-rotating column responses can be converted to one another.

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