Cyclic Behavior of Electroslag Welded Joints in Beam-to-Built-Up Box Column Steel Moment Connections

摘要

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.