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    Cyclic Behavior of Electroslag Welded Joints in Beam-to-Built-Up Box Column Steel Moment Connections
    (American Society of Civil Engineers (ASCE), 2019) Özkula, Gülen; Garai, Rupa; Lee, Peter; Uang, Chia Ming
    Steel special moment frames (SMFs) with built-up box columns are often used in taller buildings when two orthogonal axes of participating moment frames intersect. Interior diaphragm (or continuity) plates are usually required to strengthen the column at the beam flanges. A common US practice is to use the electroslag weld (ESW) process to provide complete-joint-penetration (CJP) groove welds connecting the plates to the blindside of the box column after it has been welded closed. Available research in Asia has shown that ESW joints used in this application are vulnerable to brittle fracture. Limited research and guidelines are available in US seismic design codes. The design standard for prequalified connections is primarily developed for SMF connections with wide-flange columns in strong-axis bending. To address the use of large box columns in SMFs with reduced beam section (RBS) connections, a test program with three full-scale specimens was conducted; the depth of the column section also exceeded the prequalification limit. Test results showed that the quality of ESW and SMF joint detailing was crucial for the integrity of the connections. Modifications to ESW detailing and welding process included the use of beveled containment plates intended to delay crack development that might initiate from a notch-like condition inside the flange of the box column. SMF detailing recommendations include an enlarged weld access hole geometry and steel backing treatment of the beam top flange. © 2019 American Society of Civil Engineers.
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    Development of Enhanced Seismic Compactness Requirements for Webs in Wide-Flange Steel Columns
    (American Society of Civil Engineers (ASCE), 2021) Özkula, Gülen; Uang, Chia Ming; Harris, John
    Recent full-scale testing of steel wide-flange columns under axial compression and cyclic lateral drifts for special moment frame applications showed that deep, slender columns could experience significant flexural strength degradation due to plastic hinge formation with buckling modes and considerable axial shortening within the hinge. Test results showed that the interaction between web and flange local buckling played a significant role for the observed degradation, even when the cross-sectional elements met the highly ductile limiting width-to-thickness ratios specified in the current seismic design standard for steel frames. These observations were also confirmed by numerical simulations. Enhanced limiting width-to-thickness ratios for the web of a wide-flange column for both special and intermediate steel moment frames are proposed to limit the severity of strength degradation and axial shortening. © 2021 American Society of Civil Engineers.